Dr. Samer Hattar: Timing Light, Food, & Exercise for Better Sleep, Energy & Mood

- Welcome to the Huberman Lab Podcast,

where we discuss science,

and science-based tools for everyday life.

I'm Andrew Huberman,

and I'm a Professor of Neurobiology and Ophthalmology

at Stanford School of Medicine.

Today, I have the pleasure of introducing Dr. Samer Hattar

as my guest on the Huberman Lab Podcast.

Dr. Hattar is the Chief of the Section

on Light and Circadian Rhythms

at the National Institute of Mental Health

in Bethesda, Maryland.

Dr. Hattar has many important discoveries to his name.

He was one of a handful of groups that discovered

the light sensing neurons in the eye

that set the circadian clock.

This is a fundamental discovery made in the early 2000s

that has led to an enormous number of additional discoveries

on how light regulates our sleep, our immune system,

our mood, mental health, metabolism, feeding,

and many other important processes.

If ever there was somebody who understands

how all of these processes interact

and can inform best practices for our daily behaviors,

it's Dr. Hattar.

During our discussion today, Dr. Hattar answers questions

that are absolutely essential for us to know

about our health and wellbeing.

For instance, how to align our sleep schedule

with our activity schedule, such as exercise,

and how to align light, activity and exercise

with our feeding rhythms.

He presents a new model of how light, activity,

and feeding rhythms converge to support optimal health.

And when those are not aligned correctly,

how our mental and physical health can suffer.

It's a discussion that is rich with scientific mechanism,

made clearly, of course, so everybody can understand,

as well as specific protocols to deal with shifts

in day length, shifts in activity,

and in order to optimize sleep, metabolism,

and wellbeing of various kinds.

I learned so much from Samer as I always do.

He is an absolute wealth of knowledge on all things related

to light and circadian rhythms,

physiology, and neuroscience.

I don't think you'll find anyone else

as knowledgeable about these topics as Samer.

And so, I'm delighted that he joined us here on the podcast

to share this information.

Before we begin I'd like to emphasize that this podcast

is separate from my teaching and research roles at Stanford.

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to bring zero cost to consumer information about science

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And now, my conversation with Dr. Samer Hattar.

Samer, thanks for sitting down with me.

- My pleasure. - Yeah, we go way back.

So, you are best known in scientific circles

for your work on how light impacts mood, learning, feeding,

hunger, sleep, and these sorts of topics.

So, just to kick the ball out onto the field, so to speak,

how does light impact the way we feel?

So, when I get up in the morning,

I have the opportunity to interact with light

in certain ways or to avoid light in certain ways.

I have the opportunity to interact with sunlight

or with artificial light.

Maybe you could just wade us into what the relationship is

between light and these things

like mood and hunger, et cetera.

- Sure.

So, I mean, you do appreciate the effect

of light for vision.

So, when you wake up in a beautiful area,

beautiful ocean, light is essential;

the sunrise, the sunset, blue sky, beautiful mountains.

So, that's your conscious perception of light,

but light has a completely different aspect

that is independent of conscious vision

or image forming functions.

And that's how it regulates many important

functions in your body.

I think the best that is well studied and well known

is your circadian clock.

And the word circadian comes from the word circa,

which is approximate and diem is day.

So, it's an approximate day.

Why is it an approximate day?

Because if I put you or any other human being

who have a normal circadian clock in a constant conditions

with no information about feeding time, about sleep time,

about what time it is outside,

you still have a daily rhythm,

but it's not exactly 24 hours.

So it will shift out of the solar day

because it's not exactly 24 hours,

and hence the name circadian.

- So, just to ask a quick question about that.

When you say you have this about 24 hour rhythm,

how does that rhythm show up in the tissues of our body?

- Great question.

So, it shows up at every level that we know we studied;

it shows up at the level of the cell.

It shows up at the level of the tissue,

and it shows up at your behavior.

The most obvious for you is your sleep-wake cycle.

You sleep and you're awake and sleep at the 24 hour rhythms.

And if you measure the sleep-wake cycle of humans

who are maintaining constant conditions,

you will see that the period length of the sleep rhythm

on average is more than 24 hours.

In humans it's 24.2 hours.

So you'll be drifting .2 hours every day

out of the solar day if you don't get the sunlight.

So the sunlight adjusts that approximate day

to an exact day, so now your behavior is adjusted

to the light-dark environment or the solar day.

- Okay, so if I understand correctly,

if I were to go into a cave-

- Yeah. - Or I would to be

in constant light. - Yeah.

- And I didn't close my eyes- - Yeah.

- In constant light, that I would still sleep

in one coherent about. - Yes.

- And I would still be awake for more or less one

coherent about, maybe a nap. - Yes.

- But the total duration of my day, so to speak,

would be a little bit longer than 24 hours?

- Perfect. - But if I'm in a condition

like most people are where the sun goes up

and the sun goes down, and I have some understanding

of that sunrise and sunset, then-

- You don't have the understanding,

you don't have to have conscious understanding.

You have the detection. - Right.

- So, circadian photoentrainment is the word we use,

entraining the circadian clock to the photic environment

is completely subconscious.

You're not aware of it.

It's not like vision or image forming,

where you actually know what you're looking at.

So, it's all hypothalamic.

It's part of the brain that is not consciously driven.

So, you actually do not know when it happens

or when it doesn't happen.

And that's what we'll get into when I tell you

why light affects your mood and why sometimes people

don't know how to deal with light

to improve their mood, for example.

- Okay, so this is a subconscious vision.

- Yes. - Okay.

Before you tell us about how light impacts mood,

I'm curious, what is the relevance of adjusting this clock

from a little bit longer than 24 hours to 24 hours?

I mean, it seems like a small difference,

24 hours and 40 minutes or 24 hours.

Like what's the relevance?

I mean, why should we care about that short difference?

- So, let's do the math.

If you shift out .2 hours a day,

in five days you're shifting out one hour.

So you're literally one hour off

in your social behavior in five days.

In 10 days, you're two hours off.

And if you're an organism that is living in the wild,

shifting out of the right phase of the cycle,

you could either miss food or you could become food.

So it's really essential for survival.

I think it's one of the strongest aspect of survival

for animals to have the anticipation

and the adjustment to the solar cycle.

- And for humans as well.

When you say animals, I'm assuming that applies to us?

- Absolutely, yeah. - I see.

So even though it's just a short bit longer than 24,

if that accumulates over days,

then you could find yourself very much out of phase

with the rest of your species essentially.

- Yeah, so let's say it's .2 hours.

So, in five days it's one hour.

In 25 days it could be five or six hours.

You could be in New York and you're feeling

as if you traveled from New York to London.

So, you would be having jet lag in New York,

even though you didn't do a jet lag travel.

So it's very important for the adjustment.

And if we have time, maybe we could talk about

why this is important for seasonality,

because also it allows animals to anticipate

the change in season.

And the more you're high in the north or the south,

the more that these weather changes occur very harshly,

and you have to be ready for them.

And that happens in us as well.

- All right, well, we will definitely get into seasonality.

Okay, so we've got this subconscious vision

that aligns us with the turn of the earth.

How does that work?

What is the machinery that allows that to happen?

And how does that machinery work?

- Yeah, so, we knew that in mammals, including us,

we are mammals, humans,

that the eyes are required for this function.

So, if humans are born without eyes,

or the optic nerves are damaged,

humans are not able to adjust to the solar cycle.

So we know that the eyes are required.

And since we thought we knew about the eyes a lot

before 2000, we thought that-

- You say before the year 2000?

- Before the year 2000, yes. - Mm hm, yep.

- We thought it's these photoreceptors in your retina

that allow you to see.

So, in the human retinas,

there are two types of photoreceptors;

they are called rods and cones because of their shapes.

And these rods and cones simply take the photon energy,

which light is made of,

and they change it in a way to an electrical signal

that allow us to build the image of the environment

in our cortices. - Subconsciously?

- Consciously in this situation cause it's vision, right?

It's image forming vision, it's a visual cortex,

and associative cortices, which allow you to build

conscious perception of the environment.

However, people have found, including me with the work

of David Berson and Ignacio Provencio,

that there is a subset of ganglion cells.

The ganglion cells are the cells that leave the retina,

their axon leave the retina and project to the brain.

So these were thought to only relay rod and cone information

from the light environment to the brain.

We found that a small subset of these ganglion cells

are themselves photoreceptors that were completely

missed in the retina.

And these are the photoreceptors

that relay light environment subconsciously

to the areas in the brain that have and house

the circadian clock or the circadian pacemaker,

which adjusts all the clocks in our bodies

to the central brain clock that allows them to entrain

to the 24 hour light-dark cycle.

- Incredible.

So, as I recall 'cause I was a graduate student at the time,

in the year 2000, there was this landmark discovery

made by you, Ignacio Provencio, David Berson, and others,

that these cells exists that can communicate

day and night information to the brain.

- Yeah. - In this very small

subset of cells.

Since then, I've heard, but maybe you can confirm or refute

that this system that connects the eyes

to the rest of the brain is actually the most

ancient form of vision.

That this is probably the form of vision that some early

version of human beings had before they had pattern vision,

before they could see colors and shapes

and motion and all that.

And that the same cells that perform this role

are actually similar to insect eyes.

I think I heard David Berson say once that we actually

have a little bit of the fly eye in our eye.

What's he talking about? - Yeah.

So, it's really interesting actually,

because these same ipRCGs we discovered they contribute

a little bit to image formation.

And now, work from Tiffany Schmidt specifically have proven

that they do contribute to image forming functions.

But they contribute to very limited

aspect of image formation.

So, it fits your hypothesis that these

are an ancient photoreceptors.

The other thing that adds to that hypothesis

is that they are expressed in cells that don't have

any modification that make them look like photoreceptors.

So, the photoreceptors that I told you about

that are important for vision, image formation,

they have very specialized structures that allow them

to pack these structures with photopigments;

these are the photo-detecting proteins,

so they could detect a high sensitivity of photons

that pass through them.

These new photoreceptors don't have

these specialized structures.

So they just really need a lot of light at the time,

we thought they need a lot of light to be activated.

So that's why we think they are ancient.

And that's why we think they adjust to ancient functions

that are as important as regulating

your body circadian clock to the solar environment,

to solar day or to the light-dark cycle.

- So, you mentioned ipRCGs, intrinsically photosensitive.

So these are cells that connect the eye of the brain

that behave like photoreceptors.

- Right. - Essentially.

And then you mentioned melanopsin,

which is the actual pigment that converts the light

into the electrical signal- - Yeah.

- More or less.

And my understanding is that melanopsin was identified first

in frog melanophores. - Yes.

- So does that mean that we have like little pieces

of frog skin in our eyes?

- So, honestly, David Berson say you have a fly in your eye

because it sounds better.

The more accurate I think is that you have

a frog skin in your eye.

It's not as catchy, but really,

the name melanopsin is from melanocyte opsin,

so it's melanopsin because it was found

in the frog melanocytes.

You know the frogs can change their color depending on light

and melanopsin drives this response.

So when Ignacio Provencio first discovered

these opsins in frogs,

luckily he was smart enough to see if they are expressed

in the frog eye.

They were expressed in the frog eye and it what appears

to be retinal ganglion cells, which I told you,

the one that connects the eye to the brain.

He had the insight to go and see

if they are expressed in the monkey eye.

And he found that they are also expressed in what appears

to be retinal ganglion cells,

and really that what opened the field wide open.

Then David Berson did the seminal experiment

where he went to the brain where the central oscillator,

the oscillator that drives circadian rhythm in the brain

called the suprachiasmatic nucleus,

that has been known for many years to receive retinal input.

And he labeled the cells that project there.

And then he found that even if you destroy rods and cones,

you could get light responses from these cells.

So you could imagine he nearly fainted when he saw

that these cells can respond independent,

completely in the absence of rod and cone input.

- Yeah, I'll never forget reading

those papers in 2000, 2001.

I was at the meeting in DC when Ignacio,

Iggy, we call him Iggy,

showed this image of this basically

what is frog melanophores

in the human eye. - Yes.

- [Andrew] And everyone was like,

"oh my goodness, this is the thing."

- Yeah.

- And I want to get into how light

actually can control circadian rhythms.

In a moment. - Absolutely.

- But I think it's worth mentioning now that people

who are pattern vision blind,

so people who cannot see and no conscious vision,

but have eyes, many of them still have these cells;

these melanopsin intrinsically photosensitive cells,

and can essentially match or entrain, as we say,

onto the light-dark cycle.

- In fact, they possibly have no problems

in circadian photoentrainment,

they'll have a normal sleep-wake cycle.

- But they're totally blind?

- But they are totally image blind.

And what's really interesting is that,

and this story I heard from Chuck Czeisler,

so I'll give him credit,

that some of these people who are image blind,

usually they get dry eyes and they give them a lot of pain.

And doctors used to think, oh, since they are image blind

and they're getting dry eye,

why don't you just remove their eyes?

They're not using them anymore.

And the minute they would remove their eyes,

they start having cyclical sleep problems indicating

that now they are not entraining to the light-dark cycle

and are having cyclical jet lags when their clock shifts

through the light-dark cycle.

- That's really interesting.

And I hear from a number of blind people

in my various aspects of my job,

and a lot of them have issues with sleep.

I think, in part because they don't realize that they too

need to see light at particular times of day or night

in order to match their schedule.

- Absolutely. - Well, I think

that's a perfect segue for us to talk about how light

and viewing light can impact our sleep-wake rhythms.

And then we'll move into some of the other ways in which

light can impact other forms of bodily function.

- Yeah, so I love the way you set it up

because one of the most interesting and difficult aspect

of trying to educate people about light effect

on subconscious vision is that it's subconscious.

So we're all aware of what we think is intensity

because we see the room, but if you talk to people

who know how to take photographs and stuff like that,

they know that the intensities varies greatly.

But our system, because we have to see the same way

in very bright conditions and very dim conditions,

we're not very good at estimating intensity consciously.

So when you try to tell people about intensity,

you really struggle because they think they know intensity,

but they really don't.

- You mean light intensity? - Light intensity.

- Yeah. - So the cones themselves

have an incredible ability to adapt

to different light conditions.

So you can see at all different conditions.

Otherwise it'd be a disaster.

If you don't change the setting on your camera

and you go from inside the room to the outside,

it becomes completely white, you don't see anything.

So if your cones don't adapt to the environment,

then you're not going to be able to see in this room

and on the beach, right?

But the problem is your ipRCGs,

the cells that we talked about,

they measure intensity pretty well.

They really know what intensity is.

They have a very good linear measurement of intensity.

They don't adapt as well.

They don't adapt actually that much, to be honest.

So that tells you that subconsciously the system is used

to measuring light intensity in a natural environment,

because when you are now in the natural environment,

you don't have industrialized lighting,

then your system is functioning very well.

But now when we change these environments,

we could really mess up ourselves.

So you have to teach people how to understand intensity.

And that's something that you have to explain to people.

And I think I love to do it myself.

I do it in what is called the lowest amount of light

required to allow you to see comfortably.

So you have to do this as an fun experiment.

- Okay, so explain to me how this goes.

And maybe we could break up the day

into three or four parts.

So let's say assuming that most people wake up

in the morning- - Mm hm.

- As opposed to night shift workers, et cetera,

we could talk about later. - Right.

- But they wake up in the morning,

so let's divide the day into quarters.

What is the proper way to interact with light

in the first part of the day?

- So, I honestly think the easiest thing is waking up,

get as much light as you can.

- To your eyes? - Yeah, it's really nice.

Your system is prime.

If you're entrained, it's prime to get light,

the sun should be out.

Most animals in the wild,

they actually seem to track the sun.

The sun has a huge influence on life on earth.

It's actually life on earth is because of sun.

So, that's easy.

In the morning when you wake up, you need light.

Just get the light. - Okay, so what is

the behavioral practice that you recommend?

Let's say somebody is in a condition where

there's a lot of cloud cover. - Yeah.

- Is it important to get outside?

- So, I have to tell you,

the cloudiest day is going to be much more brighter

than your room.

You could ask any photographer.

A cloudy day, unless it's really dark, dark clouds,

usually cloudy days have much more light outside

than inside the room,

even when you have good lighting inside the room.

So I think in the outside is usually even when it's cloudy,

you're going to get to enough intensity to help you adjust

your cycle to the day-night cycle.

- So, how long do you...

These are general rules of thumb,

but how long do you recommend people go outside?

- So, if you do it daily, you possibly need very few.

If you do it daily, because remember this thing

is going to happen on a daily matter.

So, let's say 15 minutes. - So, the clock is tracking

it on a regular basis? - Absolutely.

It's photon counting, it's tracking.

I would say 15 minutes.

If you don't do it daily, you may want to increase it.

And we'll talk about when you travel, what you could do,

but yeah, 15 minutes should be fine.

You do it more, it doesn't hurt.

- And through a window,

my understanding is that through a window,

it dramatically decreases the amount of light energy

coming in. - It depends on how thick

the windows are and how dark they are.

So, but it's also nice to go outside

and to feel the seasons.

- Sunglasses off?

- I don't use sunglasses.

- Yeah, but you have your Jordanian photopigment.

- Yeah, yeah, that's right. - You know, so, yeah.

Whereas my eyes are very sensitive, right?

- No, but I personally, if I'm in the shade

or if it's not incredibly bright,

I try to, especially in the morning,

but I'm also an early person.

So we have to differentiate between early-

- What time do you wake up?

- I wake up at 4:30 in the morning.

- But the sun isn't out yet. - It's not out yet, so it's-

- So, what do you do?

You turn on artificial lights?

- I usually don't turn on artificial light

because I know the sun is going to come up eventually,

but that's why I don't like the change

in the timing that they do.

- Wait, but what do you do between 4:30 a.m. and 7:00 a.m.?

- I mean, I look at my computer,

and my phone. - Oh, I see.

- So possibly I get enough light,

but in reality, I mean as long as you let your body

get the morning sunlight, which I think is really,

to me and there is no evidence of this,

but to me, if you look at all animals, plants,

this morning sunlight seems to be very important.

And we don't have experiments to show it,

but I have a gut feeling that it

has a huge impact on humans.

- Well, Jamie Zeitzer's lab at the Stanford Sleep Lab

has shown that these early morning light flashes

can adjust the total amount of sleep-

- Absolutely. - That one will get.

It makes it easier to get into sleep.

- Absolutely, absolutely.

And Ken Wright also did this beautiful camping experiments

that showed that- - Maybe you could describe

those 'cause those are beautiful experiments.

- Oh, yeah, they are beautiful experiments.

He took these college students that had a late onset

of sleep and late waking time,

and then he said, let's go camping and just don't use

any artificial light and you could go to sleep

as late or as early as you want,

and wake up as late or as early.

And he found a huge shift in their sleep pattern

just by exposing them to the light-dark cycle.

I mean, so- - And it has lasted.

- And it lasted, yeah. - Even after they came back.

- Exactly. - Those two days of camping

reset the circadian clock? - Seven days, but it lasted.

Yeah, it's pretty amazing.

Yeah, it's really incredible.

- Okay, so get bright light of some sort early in the day,

ideally sunlight, even on a cloudy day, it's going to be-

- Absolutely. - Brighter than indoor light.

- So that's easy. - Okay, so then-

- And the other thing that I would like to mention

to people, if you think it's very dim outside,

let's say it's very cloudy, stay longer.

So remember intensity is only one component.

Duration is also important because remember

that the circadian system is not like the image system.

In the image system you have to change every second

because you're looking at different objects.

You have to change your perception.

But for the circadian system it's trying to figure out

where am I in the day-night cycle?

So the more you give them the information,

the better you are.

So, if it's very bright, you don't need a lot

because it's clearly going to make you fire like crazy.

But if it's not bright, stay longer, stay for one hour.

You know, have your coffee outside or something like that.

It's just going to help.

- I think you said something extremely important,

which is that this circadian system is trying to figure out

when you are in time. - Exactly.

- Not where you are in space.

- Sorry, I said, where you are in time.

- Yeah. - I mean when you are.

- Oh no, no, I wasn't correcting you.

I just meant that I think fundamentally that's

the incredible thing about this system.

- Absolutely. - That you have this clock,

this 24 hour clock in your brain,

but it needs to be synchronized to the outside.

So could we go a little deeper into this circadian setting

behavior and come up with some general rules of thumb?

So, let's say it's a very bright day.

- Mm hm, mm hm. - Extremely bright.

No clouds, the sun's out.

You said 10 minutes, 15 minutes.

- And I'll tell you if you're sensitive,

you don't even have to go in the sun.

You could be in the shade.

There's going to be so many photons out there in the shade.

It's going to be perfect.

You don't even have to see the sun.

You don't have to have the sun.

You know, it's great for vitamin D,

that's a different story.

You could do this for your skin and protect your skin.

That's not my area of expertise,

but for that effect on the circadian system,

as long as you're outside in the shade and it's sunny day,

10 to 15 minutes should be ample amount.

- Okay and then let's say it's kind of overcast.

You know, it's not particularly bright

or there's solid cloud cover, but obviously the sun is out,

but it's not as bright.

How long do you think it would take to set the clock?

- 10 to 15 should be sufficient.

Stay for half an hour.

Stay for 45 minutes.

If it's very darker out, stay for longer.

- Okay and if for some reason,

one finds themselves very far north,

and it's very, very dense a cloud cover.

How long and at what point should somebody consider

using an artificial light source to mimic the sunlight?

- Yeah, honestly, this is where we don't have

a lot of information still, because this is where

we're going to discuss this maybe in more detail,

that if you put humans in artificial conditions,

the circadian system is very sensitive to light,

but in reality, in the real environment,

light also is affecting other aspects that are independent

of the setting of the circadian pacemaker.

- Okay. - And these which we call

the direct effect of light on mood, for example.

So, that is very hard to figure out

what intensity you need to use.

And we haven't done enough experiments

'cause this system has been discovered just recently.

But I would say if you use bright light in the morning,

and I mean, it's hard for me to give numbers.

It can get complicated.

But yeah, I mean, honestly, if you're that far north

and you're in the winter and you make sure you don't,

use these light boxes.

I would suggest that personally, but that's it.

- I use, it's actually not designed for circadian setting,

but I have a 930 lux light pad that I bought

and I bought it, they're very affordable compared

to the dawn simulating lights.

- Yeah, you don't need them.

- Which are quite expensive, frankly.

- Yeah. - And I put it there.

And so, just basically, when I wake up in the morning,

I use that until the sun comes out,

and then I make sure once the sun is out, I go outside.

But I keep that thing on all day.

And I don't know if that's good or bad.

Is a good or bad?

- I, honestly, I don't think being exposed to bright light

in the day is going to ever be bad because really

if you're outside in the day...

Unless, you know, the worst that's going to happen

if the temperature is very high,

your body's going to say don't dehydrate and go to sleep.

So you could tell actually sometimes when it's very hot,

the more you get exposed to bright light,

the sleepier you feel in the afternoon,

which is counter-intuitive. - Mm hm.

And that's to protect us, you think, against dehydration?

- I think if you think about the human evolution

from near the equator in between noon

and a certain time in the afternoon,

it would have been very hard for you to maintain

physiological homeostatic function,

being active at this very high temperature time.

So I think napping was a way,

that's why I think it has a major function which is still...

Napping was a way to somehow take you away

from that dangerous zone.

And maybe that's why people in the north they say,

in the winter we can't wake up in the morning

'cause they don't have this long light.

So, they sleep more at night.

But in the summer they say,

we feel like we can't go to sleep.

We have to put all these dark curtains.

So, I think, venturing that much up north has been...

Came up with a problem because evolution was used to

a certain light environment that was completely

changed with a human.

With other animals, I think that lived there longer,

they have come up with very interesting adaptation

of actually measuring even very small changes

in the light intensities that still occur.

And so, even if you're near the poles,

even though it's always light,

but there is a change in the light intensity

across the day-night cycle.

So, your system, if it's linear,

and remember I told you that ipRCGs are incredibly linear,

can still measure, oh, this is lower light than higher light

if the organism has the ability to do that.

- I see, yeah, it's interesting.

I've spent so much time learning from you

fortunately about these cells,

and yet I never really appreciated until now

how on the one hand they are tracking the amount of light

to understand when we are in time

relative to the 24 hour cycle,

but also that you keep mentioning this

linear measurement of intensity;

that they really are trying to figure out

when we are in time by measuring the intensity of light.

And of course the sun is the most intense source

of light available to us.

So, okay, so I think we've nailed down

that first part of the day. - Exactly.

- Basically it's get 10 to 30 minutes

depending on how bright it is,

and try and do that as often as possible to give the system

a regular source- - Daily is the best.

This system is really about,

and you'll see that even for the effect on depression,

it's about multiple days it is.

So you don't have to worry if you missed it one day,

stay longer if you want.

But if you're in a hurry and you want to do other stuff,

that's a great recommendation.

- Mm hm, so you might want to compensate with some extra time

if you missed a day or two. - Absolutely.

- And this is why I've heard you say before,

it's entirely possible to get severely jet lagged

without traveling. - Absolutely.

- Simply by staying in, being on your phone too much,

not getting the sunlight. - Absolutely.

And you saw this during the pandemic.

A lot of people mentioned that their

sleep-wake cycles suffered a lot.

Because if you're not going out and if you're staying

at home and you don't have big windows

and you're waking late, waking up late,

and then you're using very bright light too late at night,

your body is going to shift.

And now, your day is going to start instead of like

really when the sun comes up,

let's say at six o'clock in the morning,

so your day is going to start at 11 o'clock in the morning.

That's what your body's going to think

is the beginning of the day.

So, then you're not going to be able to sleep

at 10 o'clock at night,

because now that's really for your body,

it's completely different timing.

And you could see this happen during the pandemic

at a very high scale.

People get delayed in their sleep-wake cycle a lot.

- And there is this idea of chronotypes,

that we all each intrinsically have a best rhythm

of either being a morning person.

- Absolutely. - You called yourself

an early person, or a night owl,

or more of a kind of standard to bed around 10:30,

up around 7:00 type thing.

And I think there are now good data,

correct me if I'm wrong,

from the National Institutes of Mental Health and elsewhere

showing that the more we deviate from that intrinsic rhythm,

the more mental health issues

and physical health issues start to crop up.

- So, there is great data on this,

and there is a couple of things that complicate this.

The first is the people who usually are late,

they tell you that the society doesn't accommodate.

- By late, what do you mean?

People that wake up late and go to sleep late?

- Go to sleep late and wake up late.

They have an overwhelmingly higher level

of depression and failures.

I mean, clearly, I mean,

the reason the people say sleep early, wake up early,

you're better because human notice that people

who go to sleep early and wake up early,

they do better in life.

They notice that. - They just perform better?

- They perform, but the question is,

is that intrinsic to the system or is that society

because society start things usually early or late?

That's a hard question to ask-

- We discriminate against late risers.

- In a way, we discriminate, right?

But the other explanation is Ken Wright's experiment.

These late riser, if they were truly chronotypically late,

why would they shift so easily when you put them in the...

If you were really chronotypically late,

and there is a phase relation between

the light-dark environment and your circadian clock,

then doing this camping experiment should not have caused

much changes because it's not that light is going to affect you

in a certain way, it's that this is the relationship

that your body decided that I'm a late sleeper, late waking.

So, I'm honestly, I'm still unable to figure out

how much of this late waking up is controlled

by the light environment and how much is intrinsic.

I'm sure there are differences,

but are they as big as we see in the environment?

Because you have people that go off to sleep a 7:00 p.m.

and wake up at 1:00 a.m..

These are clearly advanced phase-

- So people that go to sleep at 7:00 p.m.

and wake up at 1:00 a.m.? - Yeah.

- And feel good doing that?

- I'm not so sure they feel good,

but a lot of the time you talk to people,

they say they are high achievers,

but they suffer because they go to 7:00 p.m.,

wake up advanced phase sleep syndrome.

They call it a syndrome, but then you have people

who would not be able to sleep till 5:00 a.m.,

and not be able to wake up till 3:00 p.m., right?

And I'm not so sure that the circadian system

is that variable in the human population.

I mean, clearly there are maybe some genetic factors

that make a small percentage of like everything

with the bell shape.

But I think most of the time,

the light environment may play a role.

And once, as we've talked about,

this as a long-term effect of light.

Once you get into a rhythm, and I don't mean it as a pun,

in reality, once you get into a rhythm,

it's hard to break out of that rhythm because if you start

sleeping late and waking up late,

you're not getting the morning sunlight.

- Right. - And so,

you're just going to be late.

And if you're like me waking up early,

you're getting the morning sunlight.

You're getting what Zeitzer said...

I said his last name wrong.

The one in Stanford who did the-

- Oh, Jamie Zeitzer, yeah. - Zeitzer, yeah.

- [Andrew] He actually worked for-

- Zeitzer, yeah. - Zeitzer.

So, Zeitzer and Czeisler. - Yeah, it's confusing.

- Yeah, there are a lot of zz's and i's in their names.

- Yeah. - Both phenomenal scientists.

- Yeah. - What it seems to me

is the case is that the only way to really know

if you're meant to be an early bird as they call it,

an early person or a late person,

or somewhere in between is to get morning sunlight,

and figure out whether or not that makes you feel better.

- And to understand,

to be educated about how to measure intensity.

"How to measure" I put in quotation

'cause you either get a measuring device,

but you cannot depend on your eye to measure intensity.

- Okay, so how do we do that?

'Cause you keep coming back to this.

So, that tells me that it's important.

- It's very important. - So, obviously,

so there are apps, free apps like Light Meter,

where you can walk around and hold the button down

and see how many lux are in the environment.

- These are complicated because you have to point them

to specific regions. - Right.

So, how do people start to develop an intuitive sense

of the measurement of intensity?

- Yeah, I think at one point I posted on Instagram,

how I keep my nighttime at home.

And I found out that my night vision is very strong.

So I found out that I, especially in the winter,

I only need candle lights.

So I literally use these tea lights,

and I put like 15 or 20 of them-

- How romantic. - And it's so nice.

I could see it clearly doesn't affect my circadian system.

- You and your cats- - And my wife.

- And your wife of course. - It's just great, right?

But I don't expect people to have

the same night vision as me.

So, I mean, I tell people, do the experiment.

So if you put three or four lights in your room,

switch two, sit for 15 minutes.

- Switch two off? - Switch two off.

Let's say you're using five.

And see, after 15 minutes,

you will not recognize you switched these two off.

My gut feeling is that most people would need

at least 10 times less light than they use at night to see.

The problem people use it

because most of the time they didn't

see the morning sunlight.

They are actually hungry for light without their knowledge.

So they come switch all these lights on,

but at the wrong time.

Because they woke up late.

- Okay, now I understand.

So, this morning light viewing goes way beyond-

- Absolutely, absolutely. - Setting your clock.

It's also a way to determine how little light

you need later in the day. - Exactly.

- And we're going to talk about this in a moment,

but how little light you get later in the day

is a very strong determinant of things like

when you will wake up,

whether or not you wake up feeling refreshed, et cetera.

Let's move- - And that's why,

- Yeah? - I'm going to break it

on your show, Andrew, that I'm going to tell you,

I think there is something else that people

do need to think about, which is the tripartite model.

That this model incorporate three components

we should talk about in details that allows us humans

and all animals to incorporate the circadian clock,

and its relation to light, the homeostatic drive,

and the direct effect of the environment,

which includes stress, light, all kinds of stuff.

They have to be incorporated together.

If you think, that's what I think right now,

if you think of one alone, you will always miss something.

And when you think of them as a whole,

things really become clear.

It's actually quite amazing.

- Okay, well, we will definitely want to hear

about your tripartite theory and go into detail

about those homeostatic mechanisms.

I want to make sure that for people who are thinking now,

I'm sure about light and how it impacts them.

So the morning light viewing behavior,

I like to think we've tacked down clearly.

- Absolutely. - And thank you for that

because there's so much information out there

and I've tried to relay that information.

Of course, you're my primary source

for all things circadian, as well as Jamie and others,

of course, and Matt Walker.

But I think you've made that very, very clear.

Now, let's say I've gotten my morning sunlight.

Okay, great.

Maybe my bright artificial light,

and throughout the day you said to get a lot of light.

So, I'm working at my desk.

Maybe I'll go out during the day a few times,

but I'm working at my computer, I'm doing things.

Is there anything about light viewing

in the middle of the day that people should keep in mind?

Or can they just sort of freestyle it

depending on what they're doing?

Most people are not in a dark room throughout the day-

- Yeah, so my gut feeling,

if you've got your morning sunlight,

you walk from your car slowly or you walk to work,

you didn't wear sunglasses when the lights

were still dim in the morning, that you could freestyle it.

That even if you don't get a lot of light,

there is a way to just...

In the day, you don't have to just worry about

getting a lot of bright light,

but personally, I like to do that.

So I go out at lunch and have my lunch outside as well.

This reminds the body that here it is even brighter now.

But the evidence is that you could literally

help your circadian clock by giving lights at dawn and dusk.

But again, if you think of the tripartite model,

this may be important for the circadian clock,

but is it important for your mood?

So that's where I think you need, or the homeostatic drive.

So that's where you need to think about it.

So, for the clock, for entraining your clock,

you literally can entrain it only by the dawn sunlight.

You actually don't need dawn and dusk.

People usually forget that.

- Yeah and I appreciate that you're distinguishing

between circadian effects and other effects of lights.

- Yes. - You're being very precise,

which is appreciated.

Until we hear about this tripartite model,

which we will cover, for the sake of the discussion,

let's treat the light viewing behavior

as what are the benefits or drawbacks of viewing light

for all biological purposes, not just circadian settings?

So, in the morning, it's clearly going to set the clock.

And then, during the day, if I understand correctly,

the idea is to get as much bright light as you can,

because you're feeding, it sounds like a sort of

light hunger. - Exactly.

- I see. - I love this way to put it.

I think there is a weird light hunger

considering that we're not photosynthetic organisms.

There is a weird light hungers in animals

that they need measure.

And I think that relates to the season

because the whole reproduction cycle of animals

is going to depend on the availability

of food in the environment.

And if you don't know when the season is going to happen,

they don't have calendars,

it's going to be very hard to survive.

So I think that's why we have this light hunger.

That's a major hypothesis.

It's not been tested. - Interesting.

So, then afternoon and evening start to approach.

So, I've had this weird experience.

Maybe you can psychologically or biologically

diagnosed me now, Samer.

So, where if I go into a movie in the afternoon,

like a matinee. - Uh huh.

- And I come out and it's dark,

I notice a significant drop in my mood

and my ability to go to sleep.

Whereas if I get some view of the light in the evening,

it doesn't have to be the sunset, although sunsets are nice,

but I get some light pulse in the afternoon

that I have no trouble whatsoever falling asleep.

- And this happens on a single time to watch them?

- Yeah, more or less. - Wow, that's interesting.

- And then you mentioned the camping experiment

where when they went camping,

they're seeing the sunrise and the sunset.

- [Samer] Mm hm, mm hm.

- So what should people do in the afternoon

slash evening time in terms of their light viewing behavior?

- I mean, the best thing to do is to let

the natural light creep into darkness, right?

That would be the best,

but clearly that would be inefficient.

You want to go home, you want to read,

you want to talk to your kids, you want to talk to your family.

So, I think it's nice to extend the day.

I don't think that's wrong.

If you somehow can block that light

from affecting your circadian clock.

- So, should people use blue blockers in the evening?

- I personally do not like any blockers

that take a single wavelength of light.

Because again, if you think of a holistic approach,

yes, the blue blocker is going to prevent you

from affecting your circadian clock very much.

But then your vision is going to be distorted

because we always see in full spectrum,

the sun has this beautiful spectrum, right?

And then when you start seeing without the blue,

things look yellow and it can get really weird, right?

I mean, so I personally,

I've tried the blue blocker and I couldn't even wear them.

I thought they were just really horrendous to be honest.

- Well, along the lines of blue blockers,

I think a lot of people mistakenly wear them all day long.

- Oh my God, that would be very bad.

- A lot of people do that. - That would be very bad.

- A lot of people do that.

They think that blue light is bad.

I think that the- - No, no, no.

- The concept of blue light being bad

led to a lot of product development.

And a lot of people are just assuming that viewing

blue light is what was giving them headaches.

When in fact it might've just been

looking at screens at close distance all day.

- So, here's the problem, right?

I mean, the blue light got the bad reputation

because people who gave a pure blue light

showed that it 'caused a huge retinal damage.

But again, if you're using blue light in its pure form,

it has a lot of energy because it's shorter wavelength,

but we're talking about full spectrum light.

There are ways now where you could change

the spectrum of the light and keep it white

between day and night and change the content of the color

without you noticing.

So you don't even have to affect your vision.

- So how would you go about doing that?

- So, you just lower the level of the blue light.

You don't have to eliminate it.

- So just dim the lights?

- Dim the blue, then increase the yellow,

but keep all the colors in a certain white.

So, you know, you could have different warmness of white.

And people know how to do this.

Physicist know how to do this.

People who work with light know how to do this.

- Well, maybe somebody in the wellness slash,

I don't like the word, but biohacking,

or optical community will do this.

I think it's really important, I see so many people

wearing blue blockers. - They have meetings now.

I don't know why they block-

- Well, I think they're just uninformed.

I think, frankly- - Yeah and to be honest,

it's easy, right?

It's easier to explain to somebody if ipRCGs

respond mostly to blue, remove blue, you'll be fine.

- Right, right. - Right?

But that's not as simple as that because they also receive

rod and cone input.

So you want to actually...

And we could go into details,

that's boring for your listeners,

but it also affect the adaptation

properties of the whole retina.

So you don't want to do something so drastic

that you take just one color of the spectrum.

It just seems very counter intuitive to me, to be honest.

- You've told me before as well,

that just because these intrinsically photosensitive

circadian setting ganglion cells respond best to blue light,

if the light is bright enough because they also get input

from other components of the eye,

it doesn't matter if you block the blues.

- Yeah. - If you're looking

at bright light at night,

you're going to disrupt your circadian cycle.

- Absolutely and that's why I didn't want to

go into the boring details,

but themselves, the photoreceptors have a wide range

of responsiveness.

So they are more sensitive to blue light,

but that doesn't mean they don't respond to green light

or to shorter than blue light.

They respond to very, very wide spectrum

with different sensitivity.

So unless you understand the system just removing 480,

I don't think it's going to do- - 480 nanometers, yeah.

So, your home is a cave at night basically with some-

- It's a nice cave. - It's nice cave.

- Yeah. - With candles.

- That's right. - Right and you and your cats-

- And I watch TV and dim it. - And your lovely wife.

- Yeah. - Who I know, who's also

a phenomenal scientist in her own right.

- Thank you, yeah, she is.

- She is.

But you do keep your home quite dim

to dark at night? - Yeah.

In fact, I did go to meetings with some of my friends

who work on this and they really struggled with me.

They said we could have broken our legs living

in the same light environment that you do.

So I am an extreme, but I measured it for myself.

And I asked, Rejji, my wife, if she's okay with it.

She also liked the dimness.

Both of us can see well in dim conditions.

And that helps us a lot,

but I think you have to measure it for yourself.

You really have to...

It's a very simple experiment.

Just try to dim the light as much as you can.

I call it the minimum amount of light

you require to see comfortably.

- And that's how you want your environment

ideally at night? - At night.

This is what I think is the game changer.

If you reach to a level where it's just barely,

you're literally on the cusp of seeing uncomfortably

versus seeing very comfortably,

you are going to be very much better than

I don't like to make it completely dark.

I think complete darkness induce anxiety

in humans, to be honest.

So I don't like complete darkness.

- Kids don't like complete darkness.

They like a nightlight. - Even animal,

even nocturnal animals don't like complete darkness.

I mean, we have studies in animals that are nocturnal,

that if you put them in complete darkness for several weeks,

they have severe anxiety and depression like effect.

So keep the light dim, use red light that is very dim,

if you want to keep the room for sleeping.

Red light that is very dim has very small effect

on the circadian clock.

And below 10 lux of red light,

literally doesn't affect sleep at all.

So there are ways to do it.

It's just we need to educate the public.

And I feel like you literally need a whole lecture

to just explain to the people how to deal with light

because it's not as simple as people think.

- Well, that's what we're doing here.

- Yeah. - We're stepping through it

piece by piece and the reason we're doing that

is because it's not as simple as saying,

just block blue light or get a lot of light during the day,

and minimal at night. - I mean, just to put it

in perspective and tell that we only have

three different cones in our retina

that respond to three different colors.

We call them red cones for simplicity,

green cones and blue cones.

Yet we have only three of these,

but we could see massive palette of colors.

So that tells you something.

If the system was just simply about a single color

and us just removing 480 or just blue is sufficient,

then we should only see in red, yellow, and blue.

We shouldn't see all these different hues of color,

but because the system is not that,

we see all these different colors.

And that's why it's important to remind people

that the white light is made of many different colors.

It's actually like the rainbow.

That's why you see the rainbow, it's made of many colors.

White light is never truly white.

It's made of lot of different colors.

- It's like the Pink Floyd album cover.

- Exactly. - With the light coming

through the prism. - Exactly, exactly.

- So, dim at night, maybe dim red light ideally,

or candle light.

Find that minimum required light level.

- Test it, just make sure when you lower the lights,

sit for at least 10 to 15 minutes, let your system adapt.

Because if you had a bright light and you switch it off,

surely you're going to suffer because your system

didn't adapt yet; it was used to very bright light.

So you want to engage your rods,

which take a long time to dark adapt.

So that's why I tell you, just wait a little bit.

Don't just switch it off and now I don't see, put it on.

Put it off, sit down, wait for 10 minutes,

ideally 15 minutes and then see how you see.

And then once you do that, you will notice that actually,

yeah, I could see quite well even with much less light.

- What do you do regarding screens?

- Yeah, that's the hardest thing.

Again, I mean, there are beautiful programs

that change the whole intensity and color of the screen.

These could help dim your screen at night

to the lowest part.

I mean, yes, you won't see it

when you wake up in the morning,

but then you can increase that intensity.

So, try to decrease.

I mean, just what we were talking about.

Think of light intensity, duration, color, and time of day.

You really have to keep these four things together, right?

- We've roomed together at a couple meetings

from time to time, no longer,

because one of us not to be named has a severe snoring issue

that made the other one pseudo-homicidal.

[Samer laughing]

You can guess who that was.

But I've seen you check your phone

after dark once or twice. - Mm hm.

- And you did it by sort of pointing your phone

away from you, right? - Exactly, yep, absolutely.

- And actually I'm sort of half joking,

and you dim it quite a bit. - Yeah, dim it quite a lot.

- I'm sort of half joking,

but it actually makes sense that if you shine

a flashlight in your eye,

it's much brighter than if you shine a flashlight-

- Light only go in direct line,

so if you'd just look on the side,

most of the light is going to go this way,

and you're only seeing this way.

- Okay, so, and as silly as that might seem

to people listening, I mean what it means

is that getting bright light in your eyes at night

is something that you really want to avoid.

But there is the reality that-

- And even when I check sometimes if I have something,

and I check it so fast and switch it off so fast.

So I'm also aware of duration- - Not my messages.

- I'm also aware of the duration, right?

So duration, intensity, color, and time of day.

Ideally I should not check iPhones an iPads.

I don't use iPad at night because it's hard

to lower it enough 'cause it's a huge.

But even my iPhone, I try not to use it at night.

And like once it becomes 8:30 or 9:00,

I don't look at it at all. - Unless it's World Cup

or Euro Cup, in which case Samer's on 24 hours, everybody.

- Right, that's only every four years.

- He's a big soccer fan.

All right, this has been incredibly, no pun, illuminating.

Let's talk about the relationship between light

and some of these other non-circadian

or pseudo-circadian effects.

And we will try and link those.

But you had a what I consider absolutely landmark

beautiful paper published in "Nature" a few years ago,

showing that if you disrupt the exposure to light

or the timing of the exposure to light

that there are dramatic effects on the stress system

and on the learning and memory system.

Maybe we could talk about each of those

separately or together.

What are the effects on stress and the effects on learning

when light viewing behavior

and sleep-wake cycles are disrupted?

- Yeah, so just to remind you, you know that,

but to remind your listeners that I was trained

as a circadian biologist.

So I really was indoctrinated into thinking that light

has to affect the clock,

which then caused all these different effects.

So, that's what I believe.

That's my dogma.

That's what have made me really happy.

And then Tara LeGates and Cara Altimus joined the lab

and we started discussing a lot of data.

And we said, what if there is a direct effect of light

that we're missing, independent of the circadian clock?

So this is not an easy question to us to answer,

because as we've been talking all along,

light affects the circadian clock.

So how could you give light at different times of the day

and not mess up the circadian clock?

Luckily, we came up with such a way,

and that's why it was important to do these experiments

the way we did them.

And we proved that this light-dark cycle

does not disrupt the clock,

there is still a circadian rhythm,

and does not cause sleep deprivation.

And yet, surprisingly, if you give light

at the wrong time of the day,

even without disrupting the circadian clock

or without causing sleep deprivation,

as you mentioned you get the huge mood changes

in the organisms and you get learning deficit.

So, this really, and at the time people have really

hit us hard.

I mean, it was really hard to publish this work

and you could, yeah.

- Well, it came out in "Nature."

- Yeah. - So in the end you prevailed,

but I want to make sure that I understand.

So, you're saying that yes,

there are effects of light on the circadian rhythm.

- Absolutely. - Sleep meaning

sleep and wakefulness. - Yes.

- And their timing.

However, there are direct effects of light on mood

that can be dissociated from the effects

on sleep and waking. - Absolutely.

- So if I interpret that correctly,

that could mean that when we view light and how much light,

could make us feel happier or less happy or even depressed,

stressed, learning, et cetera.

- Bingo. - Even if we're sleeping

and waking up at the appropriate time?

- Bingo.

I mean, eventually because we're talking

about the whole system,

eventually when you start having the other problems,

you also develop sleep problems,

but you're absolutely right.

And in fact, now, research from Diego Fernandez

in the lab have found that now we know that they actually

require different brain regions.

So we don't only have a theory,

we don't only have a light environment

that showed they can be dissociated,

we know that they use completely different brain regions.

So, the SCN that I told you about earlier,

the place where the central pacemaker is,

the one that receives direct input from the retina

through the ipRCGs to adjust your circadian clock

is not the area that receives the light input

for mood regulation.

It's a completely different brain region.

- What's the brain region called?

- So the brain region,

we called it the perihabenular nucleus.

I'm not so sure how good or bad the name,

but it doesn't matter, it's that PHb.

And what's really amazing,

this region also receives direct input

from the ipRCGs, but projects to areas in the brain

that are known to regulate mood,

including the ventromedial prefrontal cortex,

which has been studied for many years

to be impacted in the human depression.

So just by this amazing serendipity

to find that a region that is so deep in the advanced brain,

like the prefrontal cortex is your executive brain,

one of the most elaborated in humans,

to see that they receive inputs from

these ancient photoreceptor was stunning to us,

and told us how much we didn't understand

the importance of light on a human behavior.

- So, how does that finding inform daily protocols

for you or for other people?

I realize you can't leap always from one paper-

- Absolutely, yes. - To daily protocol.

But if light indeed does control prefrontal cortex,

executive function, learning, stress and mood,

and let's say I'm waking up each morning and I'm sleeping.

What should I do different?

- That's why we came up with the tripartite model

because yes, we could think about just adjusting the clock

with lights in and being dark throughout the day.

But that may not be important

for your whole physiological function.

So, now, if we include these other effects of light,

that's why I prefer to still get a lot of light in the day.

I don't want to be in very dim light condition

throughout the day. - I see.

- So, even though it doesn't affect your clock,

as you beautifully said, Andrew,

it may affect your mood and learning and memory.

It may affect your alertness level,

which is going to allow you to learn better.

It may affect your homeostatic drive,

maybe your homeostatic factor would go higher

so you could sleep earlier.

So it's important to think of light as stimulating

all these brain regions,

which means it's producing more activity,

which in reality this is how people think

of the homeostatic drive, that the more active you are,

the more the homeostatic drive is built up,

the better you sleep.

So that's why we came up with the tripartite model

because as a circadian biologist,

I only thought of light through the circadian clock

affecting behavior.

As a sleep biologist, they only thought of the homeostatic

drive affecting sleep, affecting behavior.

And for people who study light for vision and other form,

they thought only of the environmental input.

But now if you put them all together,

you get with this tripartite model

where it's really mind boggling.

And it makes so much sense.

The organism doesn't want to depend on a single component,

but if you could incorporate these three together,

you could have a beautiful system that is well adapted.

So let me tell you the sleep-wake cycle, right?

So we know that there is a homeostatic drive

to affect sleep.

You've had beautiful talks about that.

- Which is basically the longer you're awake,

the more you want to be asleep.

- So, that's your homeostatic drive.

We've talked about the circadian influence of sleep

and the fact that light-dark cycle

affect the circadian system, which eventually affects sleep.

So these two components are well understood.

Now the third factor is your direct light

or environmental input.

How much stress, how much light you get from there

also can highly impact sleep.

So even if you have a good circadian and homeostatic drive,

if you're getting light at the wrong time of the day,

or if you're being stressed and thinking a lot,

then your sleep is going to suffer.

So you have to think of the three together

to have a beautiful sleep-wake cycle.

- I see. - And that's why

we came up with the tripartite model.

The same thing happens with feeding.

I could beautifully put it to people.

Your hunger, your energy level is measured

by the arcuate nucleus.

Your daily intake of food is again,

dependent on the SCN and light-dark input.

We found that if food is not available,

there is yet a third input that is not depending on the SCN,

not depend on the arcuate,

depending on a completely different brain regions.

So the animal can actually start looking

or the human can start looking for food when it's scarce,

even at time when they are not supposed to be active.

So, that's how the organism think,

they have to evaluate multiple inputs for them to decide

what is the best physiological outcome

at that moment, at that season?

- I see.

So, I want to get into arcuate and feeding,

but just to make sure we can keep our hands

around this tripartite model.

So, if I understand correctly,

we've got the circadian influence,

then you've also got the drive to sleep.

- Right. - Actually, one of the ways

that I think that can be best understood is if somebody

ever pulls an all-nighter,

they get tired around 11:00 or 12:00 or so,

and then very tired around 3:00, 4:00 a.m.,

but then even if you stay up sometime right around

7:00 or 8:00 a.m., your normal wake up time,

you start to feel alert again.

- Exactly. - And that's because

the sleep drive is extremely strong,

but there's a circadian rhythm that drives

wakefulness in the morning. - Exactly.

- Okay, so that's two are the components.

- [Samer] Right.

- Before we get into the feeding component,

I want to talk about these direct effects

of light on mood. - Mm hm.

- Okay, Diego Fernandez's data.

And this perihabenular thing. - Sure.

- So, let's just for the moment set aside the tri part

of the tripartite model and just focus on

what are the direct effects of light on mood?

And the way that I interpret what you've said so far

is that the protocol that emerges from this

if one trying to optimize their mood is,

yes, see light, view light I should say, early in the day,

in order to set your circadian clock.

Maybe also in the evening as well.

And of course, avoid light at night,

get it as dim as possible.

However, you said, it's also a good idea to get

as much bright light during the day as you safely can,

in order to improve your mood independently

of regulating your sleep-wake cycle.

- And that's the hypothesis.

Here's the problem where it's not going to be

as satisfying as the circadian is that as you know,

this brain region has been discovered very recently.

- Habenula? - The perihabenular region.

- Well, we've known about it a long time,

but nobody knew what it did.

- So, we knew about the habenula,

but that's why the name is confusing.

It's actually not the habenula itself.

It's the perihabenular. - Oh, near the habenula.

- It's near the habenula.

- Why don't you just call it the Samer Hattar nucleus?

- I should have.

I don't know why I haven't done that.

- Maybe 'cause if you do that, it's not okay.

Okay, so for here ever after the perihabenular nucleus,

we should probably call it the Hattar-

- The Hattar-Fernandez.

- How about Hattar-Fernandez-Berson nucleus.

- Yeah, that should- - Okay, this is like nerdy

science attribution stuff, but I'm just going to call it

the Hattar nucleus.

Wikipedia, line it up.

Okay, so this structure is taking light,

and independent of sleep rhythms and circadian rhythms,

it's driving changes in mood. - Something.

- How does it do that?

Is this through the dopamine system?

The serotonin system? - We still recently,

we haven't identified this region very well.

We don't know what light does to it.

We don't know how it interacts.

So this is an area that is ripe for discoveries

and we're working on this right now.

But that's why I said, it's not satisfying.

This is like the function of sleep.

Why do we sleep?

We know sleep is very important to us,

but we still don't have a satisfying function

of why do we sleep, right?

- I see but the why questions- - We have hypothesis.

- The why questions, I think it's our good friend

and colleague at University of Washington,

Russ Van Gelder, who always says,

when somebody asks why, that the best answer is just to say,

I wasn't consulted at the design phase.

- Yeah, exactly. - Right, none of us

really know why. - No, but the point is

maybe I shouldn't have said why,

what is the function of sleep?

It's still very hard to know.

What is the reason organisms have to go offline for so long?

You know, people assume it's for repair,

assume it's for learning and memory,

assume all kind of stuff,

but there is really no clear function for sleeping.

There is no clear function for sleeping.

I mean, if you talk to people, there are hypotheses.

- I mean, all we know is that if you don't sleep-

- Exactly. - Or your sleep

is very fractured, you get messed up.

- And you could die even, right?

I mean, it's really bad if you don't sleep,

but we don't know what is the function?

What is that sleep have done to organisms

that couldn't have done with rest?

What if you just could rest without sleeping?

Just sit down and rest.

- Well, my lab is trying to figure out whether or not

these non-sleep deep rest protocols

can compensate for sleep.

- That would be interesting. - I mean, obviously sleep

is better, but many people are not getting

the sleep that they need.

- Right. - But, okay.

So, and if people are sensing that Samer and I

are about to start talking over each other and arguing,

that's always the goal

when we talk, right? - That's right.

- Unlike other scientists I interact with,

when Samer and I get together,

it's considered a successful conversation

if we get into a big fight,

and then go for a big meal- - That's right.

- Where I pick the restaurant. [Samer chuckling]

Okay, so let's talk about food and eating and appetite.

You had yet another, yes, I greatly admire your success

in this way, yet another incredible discovery

showing that there are direct effects of light

on appetite and feeding behavior.

Okay, maybe you could just summarize

those results for people.

- Honestly, that paper is the one that allowed us

to come with the tripartite model,

because we were thinking completely wrong about it.

We wanted, this experiment, it'd be fun for your audience

to hear why we started this experiment.

Remember that when we discovered the ipRCGs,

we figured if they are the only relay

to entrain the circadian clock,

then you could kill them and have an animal opposite

to the one that we spoke or a human opposite to the one

that we spoke about earlier.

Where instead of having no pattern vision

and have circadian photoentrainment,

we could produce an animal that have pattern vision,

but no circadian photoentrainment.

- Hm, so circadian blind.

- Circadian blind, but pattern sighted.

And we succeeded in that.

The problem when you have these animals,

which I've told you many times already

is that they don't adjust to the day-night cycle.

So doing experiments on them become very complicated.

- What is their behavior like if you don't have these cells?

Are they awake and then asleep, awake and then asleep?

- They just drift like the humans we've talked about.

- They think they're in Las Vegas

with no clocks or watch- - They drift, exactly.

- They stay up later every night and go to sleep-

- They can either, depend on their clock.

If their clock is shorter, they come in earlier.

If their clock is longer, they come in later.

- So they're really messed up?

- They really don't adjust to it.

If they were in the wild,

they'll be eliminated in a second, right?

There is no way they'll survive.

So, me and Diego started talking and we're like,

what if we use non-light in training agent?

And what is the strongest non-light in training agent?

Food.

So we thought that the light defective animals

will have more sensitivity to food entrainment

because as you know more than me,

this is an area that you've worked really well on,

for vision, if you're image blind,

your hearing and somatosensory get improved, right?

The lack of vision improves your hearing and sensation.

But we found actually that if you don't have

the light to system, actually the food ability to entrain

the animal goes completely to the ground.

Completely opposite to what we predicted.

- So light viewing and feeding behavior are interacting

in ways that support one another.

- And that's why we came with the tripartite model.

We figured it's different than sensation of the environment.

When you sense with vision, vision and hearing interact,

but your vision is a real full modality.

You want to see.

That's what vision wants to do.

You want to hear.

That's what hearing wants to do.

You want to sense.

That's what sensing want to do.

But for the circadian system, light, food,

all these entraining agent,

they somehow have to interact to keep a coherent system.

You don't just assume if you remove light,

this one is going to be stronger.

No, they need to know each others.

The light informs when the animal is going to eat.

- Well, what I like about this so much is that

in the world outside of science,

in which I don't really exist in, but that I see a lot of,

this kind of wellness and stuff with

all this mind-body integration stuff.

It's interesting because people view the body

more as a system, right?

A system of organs that interact,

as opposed to the way that standard science

and medical profession is like,

you work on the liver or you're ear, nose and throat,

or heart and lung, or brain or-

- Wow, that's a great way of thinking about it.

- But the biology is integrated.

- Yeah. - And so, for somebody who's

interested in effecting their eating behavior,

something that you are familiar with,

and that we will talk more about

your experiences of in a moment,

how should they use light in order to adjust

their eating behavior? - Right.

So, now that I've told you about all these interaction

between the different inputs to the circadian clock,

just you think about it as an engineer,

what would be the best thing?

The best thing is to know when your food times happen

in the day, when should you get light,

and when is your circadian clock in your system, right?

So, if you eat at very specific times of the day,

that's another signal that is telling your body, your clock,

you're in a certain time of the day.

So if you're having lunch at the correct time every day,

and you're getting bright light,

now you have two systems that are informing your clock,

your clock is going to be better.

- So regular mealtimes?

- Regular mealtimes that fit your circadian clock.

So, and in fact, if you do that, when I started doing this,

and it helped me lose weight,

is that I'm exposing myself to the right amount

of light-dark cycle, I'm eating at regular time.

It is amazing.

You would be not hungry, let's say you eat at noon,

you will not feel any hunger at 11:45.

And then all of a sudden the hunger jumps.

This is clearly not an energy issue

because it could not be that drastic.

- No, the desire to eat is mainly driven by these cues,

these hormone cues that are very exquisitely timed to-

- Exactly. - Sleep-wake cycle,

but also to light. - Exactly.

And you know, in the wild,

you could imagine why energy level

through the arcuate nucleus-

- You should explain to people what the arcuate is

'cause I don't think we've done that adequately.

The arcuate nucleus is an area of the hypothalamus

that drives hunger and feeding behavior.

And what we're talking about is the fact that

it's taking cues from your viewing of light,

believe it or not, is impacting your level of hunger.

And this is a non-trivial way in which your timing of hunger

and amount of hunger is regulated by when

and how much light you view.

So, let me ask you a couple of practical-

- But can I just, this is really, before you asked me-

- Sure. - Sorry, Andrew.

We said we are going to fight, but to me,

the interesting thing to think about it,

in the wild when you didn't have the availability

of food that we have, the arcuate plays a huge

important role because if you weren't successful

in getting food, then the arcuate is going to tell you,

look, you have to take risks and go get food

because your energy level is very low.

And that's great, there's tons of great research about that.

But I think what's missing is the fact in humans,

we're not getting to a situation...

Most of us, we're not getting to a situation

where we have low energy levels.

Most of the time actually we eat not because

we are really have low energy,

but because we want to eat.

So I think that's why I feel that the timing

is very important for us because we always

have enough energy level for us to eat.

- Well, I mean, I enjoy eating so much that I'll eat

just for the sensation of chewing.

- True, true. - I mean,

I enjoy the taste too. - True, absolutely.

- And I enjoy the social aspects

when those are a part of it. - Absolutely.

- But I literally enjoyed the physical act of chewing.

- [Samer] Absolutely, absolutely.

Uh huh. - Which explains a lot.

Okay, so how regular are you or do you recommend

people be about mealtimes?

Because what I'm hearing is that light viewing behavior

is pretty straightforward.

Get a lot of light in the morning and throughout the day,

minimize it in the evening and at night, generally speaking,

for sake of mood and circadian rhythm.

But for sake of regulating timing and quality

I should also say of food intake,

because people clearly make better choices about food intake

when they are anticipating a meal

and they aren't constantly hungry.

And so, the ability to regulate hunger for particular phases

of the circadian cycle is quite valuable for all people.

Not just people trying to lose weight, but all people.

Are we talking about down to the minute?

- Absolutely not.

- All right, so 12:00 noon is my normal lunch,

let's say plus or minus?

- Half an hour. - Okay.

So eat around between 11:30 and 12:30.

- If that's the time.

And it depends if you also do multiple meals.

Remember three meals, that's a decision that somebody

came up with, I don't know why.

- And nowadays, fewer people are doing that I think.

- Yeah. - Given our friend,

Satchin Panda's work. - Right.

I mean, so you could have two meals,

you could have very multiple meals that are distributed

across your active time.

I agree with Satchin Panda's work that try to avoid eating

when your system is supposed to be relaxing,

when you're supposed to be at non-active times.

So, limit your eating to the active time of your cycle.

And that seemed to be, and Joe Takashi

is doing some beautiful stuff on this,

that seems to be incredibly important

for aspect of the circadian.

- And for health. - And for health.

- Yeah, we're referring to Satchin Panda's work,

he wrote a beautiful book called "The Circadian Code."

Maybe Samer, with some luck you'll write a book as well.

Meaning the world will be lucky to have that book,

but Satchin's data really strongly point to the fact

that liver health, brain health, metabolic factors,

and endocrine factors of various systems and organs

all seem to benefit from having a period of each 24 hour day

in which we are not eating anything

and then eating at very regular mealtimes.

- [Samer] Absolutely.

- Let's talk about eating and mealtimes

and let's move a little bit away

from the science for the moment,

although we will return to it,

and talk a little bit more about your experience

with eating and mealtimes.

So, you're looking in good shape lately.

- Thank you. - I know you've been

putting work into it. - Yeah.

- We talk a lot and you've been exercising

and you've been eating well, meaning quality food.

You just came back from Jordan

where I'm assuming the food is amazing.

- Yes, the food is amazing and honestly,

usually I gain a lot of weight in Jordan,

but this time I didn't gain any weight,

which was really nice, so.

- Yeah, when I met you, you were probably about 100 pounds

heavier than you are now.

- Yeah, 275 pounds.

I'm 219 now.

It's crazy, yeah. - You had a lot of vigor then,

and you have a lot of vigor now,

but I know that you undertook a very specific protocol

in order to lose the weight,

based on your understanding of the circadian system-

- Yes! - And of light,

and appetite and mood.

Maybe you could just tell us a little bit about

what that schedule looks like.

And we realize that this is not a prescriptive

for everybody, but you found what worked for you.

- Yeah. - To maybe just describe

those changes. - I mean, honestly,

I followed my circadian cycle, right?

Of what we've talked about, right?

So I dimmed the light at night, I slept at regular hours,

I ate my major food in breakfast and lunch

when I'm really active and I'm really hungry.

And at night when I avoid dinner,

because my circadian system really shuts off at 3:00.

I'm an early person.

Like you could give me anything I would eat before 3:00,

after 3:00, nothing appeals to me anymore.

My system is shut off.

- Well, what time are you going to sleep?

And what time are you waking up?

- Oh, so in my case, I should have put this up.

I mean, I go to sleep literally at 9:00 p.m..

I mean, I literally five minutes after 9:00 p.m.,

I'm completely out.

And I wake up between 4:30 and 5:00 a.m..

So if I extend it, I go to 6:00 a.m.,

but very rarely.

It depends on how tired I was.

- And that, as I recall, was an important set of changes

for you to be able to- - Absolutely.

- Regulate your food intake.

- Absolutely because then I'm having very big breakfast,

and again for different people it's different,

I have a big breakfast at 7:00 a.m. maximum.

So I have a big breakfast, coffee, and all this stuff.

Then I have some simple snack around 10:00.

Then I have regularly lunch at noon,

or between noon to 1:00.

Then I have another snack at 3:00.

And the hardest time to regulate the food

is between 12:00 and 3:00.

This is when I really feel hungry all the time.

- This is your equivalent of kind of

late evening for most people.

- Yes! - So for me,

it would probably be between 7:00 and 10:00 p.m..

- Exactly, exactly. - Got it.

- And then at night I'm completely not hungry,

but usually as you said,

the beauty or the enjoyment of food,

like when my wife cooks some really beautiful Indian food,

I eat, but I'm not hungry.

And I notice if I eat with that, I usually gain weight.

But if I regulate that at night, I also lose weight.

So there is a combination of all these things that help you

adjust the input of food, the input of light,

the input of the clock, and the drive to hunger.

- Yeah, I appreciate you sharing that.

And I want to emphasize that some people

are not hungry early in the day.

They might be late shifted people.

- Exactly. - In which case,

eating later in the day will work well for them.

- It will work well as long as they don't eat

early in the morning.

That's just, you have to work with your schedule,

with your active schedule.

- Yeah, you and I have been talking

about this offline for years.

I'm glad we're finally having this discussion publicly now.

What we're talking about really is finding

your ideal sleep schedule.

- Exactly, exactly. - And finding your ideal

eating schedule. - Exactly.

- And understanding how those two things interact.

- And do you know the nice thing, as you said,

finding them out is going to help you

to understand how they interact

because we know from the tripartite model

that they are all interconnected.

And for each person they're going to be

interconnected differently.

So, for each person you would...

You know, for me, if I exercise at night,

I'm going to mess up my whole system.

- When do you exercise? - Morning.

Morning works great for me.

I mean, it's amazing.

Morning exercise for me works great.

If I tried one time, because it was easier for me

to exercise at night before I leave,

when the traffic is there from the night.

And I think that messed me up because I couldn't sleep well

and I couldn't wake up well.

And that led to more changes in my food.

I gained weight again actually, believe it or not,

even though I was exercising.

So I think this really makes me think that you have to think

of the tripartite model to see what is the best times

and what is the best interrelation between

the different component, as you beautifully said,

between your mealtimes, your light exposure,

and your sleep that works for you.

- Well, thanks for that.

Usually Samer's insulting me.

Today, he's complimenting me.

I'm going to compliment him right back by saying,

this is the first time that I've ever really understood

how yes, light can control sleep.

Yes, it control mood.

Yes, it can impact feeding,

but that it's really about doing the self exploration

to align those in the way that works best.

And what I'm hearing, tell me if I'm wrong,

but what I'm hearing is that once you understand

what gives you the best sleep-wake cycle,

then you should exercise during the period of time

in which you feel most alert.

And if it works for your schedule,

ideally you would also eat during the time in which

you feel most alert and then stop eating

and stop light viewing behavior as you head towards sleep.

- Right.

So, the only thing I would say that complicates all of this,

and that's what makes me sad, is your light exposure.

- Mine personally? - Sorry.

- No, I'm just kidding.

- The people's light exposure, right?

This is what complicates it because you're not going to be able

to figure all this out if you're shifting yourself

out of your comfort zone.

- By viewing- - By viewing light

at the wrong time of the day.

So, let's say if you were under an ideal natural conditions,

you're a person who would sleep later than me.

Let's say we'll sleep at midnight and wake up at 8:00 a.m..

Let's say you don't eat anything till noon,

and as you said, you eat late in the evening.

Then this would be perfect for you,

but now see what happens if now you include

the light component.

Now, if you push your sleep from midnight to 4:00 a.m.,

now you're waking up in the morning and you're actually

really not the morning...

You're working, I'm sorry, at noon instead of eight o'clock,

and the time where you're not supposed to be hungry,

now you're going to start eating directly at noon

or something like that, or even delay it.

And now you're shifting your whole cycle.

And you don't know if this interaction between your sleep,

feeding and the light-dark environment

are still going to be maintained or not.

And that's the problem that people have.

- So, as I'm hearing this what I'm realizing is most of us,

probably me included, are messing up at least one, two,

or three of these components. - Exactly, exactly.

- But that the probe, the way to figure out what's right

for oneself is to start manipulating light exposure.

- Right and I'm going to be honest,

I'm biased 'cause I believe that light

is the strongest time giver.

And a lot of people disagree.

Some people think feeding is.

- I always thought that light was the primary zeitgeber,

the primary light- - Yeah, but a lot of people

think it's food.

A lot of people even sometimes mentioned social interaction.

- Have they read the literature?

- I agree with you.

I totally agree with you.

- I mean, my understanding is that light

is the most powerful driver- - Absolutely.

- Of the things we're talking about.

- That's why I think we need to regulate this first

and everything else fits.

And you know, the nice thing is that your sleep-wake cycle

and exercise tell you really bluntly

if you're doing it right or not.

- Tell me more about that. - I'll tell you more.

When I shifted my exercise, honestly,

things fell apart like never before.

- When you moved from exercising early in the day

to late in the day? - In the morn, yeah.

It completely fell apart for me.

I didn't enjoy exercise at night.

My pain tolerance for exercise wasn't as good.

I'm talking with N equals one and I'm aware of this.

I've never tested this empirically, but at least to me,

it really messed up everything.

I started having problem because my body temperature

would go up and that will affect my sleep.

I possibly was running in the gym with a lot of lights.

So maybe the light was a component, but for me,

exercising in the morning, it's so much better for me.

But a lot of people can't even

think of exercising in the morning.

So it depends on when you feel comfortable

in your sleep-wake cycle and your exercise.

I think that tells you if your system

is in synchrony with one another.

- That's really interesting.

We're good friends, our friend, Pat Dossett,

that we both know. - Mm hm, oh, absolutely.

- He did nine years in the Seal Teams.

And he's one of these people he says,

he's happy to go for a run or a swim anytime

between 4:30 a.m. and 6:00 a.m..

And he'll train in the afternoon too

'cause he's a Seal Team guy and they'll do whatever anytime,

that's part of the phenotype,

but he feels best doing that, right?

I like to exercise mid-morning.

- Interesting. - And I'm happy to skip eating

until 12 or 1:00. - Great.

- And I like to go to sleep around 11:30, 12:00,

'cause I'm a normal human being rather than you

who goes to bed at 9:00 p.m. - What about Pat actually?

I've never asked him what time.

- Pat?

So, Pat's ideal to sleep time, I've asked him this,

would be around 8:30 or 9:00 except now-

- Oh, so I'm like Pat! - Yes, but he has two

young children, two years old and a newborn.

And so, the cycle is disrupted, right?

- Yeah, but that's known, right?

I mean the effect of childbearing.

- Right. - And I think that we could

talk about this, that's more complicated-

- Right. - But that's pretty much.

- Yeah, I mean, I think we need to come up with a new name

for chronotype because- - I agree, I agree.

- Chronotype implies that it's just about sleep and wake;

being an early bird or a night owl.

And what we're also talking about is how exercise

and eating match onto those.

- The the phase relation between them.

- Right. - And the phases between

different components, as you said.

- 'Cause they interact. - Because they interact.

- Right. - And they don't have

to be in the same phase.

Like let's say my light and food

could be very close to each other.

Your light and food could be different, right?

The phases don't have to be, they can be plastic.

So you have to find this for yourself.

You maybe you're a person who eats late at night,

exercises late at night,

or you may be a person who exercise early, eat later.

So, as long as the phase is good,

that's what you have to find out.

- Okay and if I understand correctly,

when you're talking about phase relationship,

it means you want to lump exercise, feeding and light for-

- And sleep. - And sleep in a way

that as a coherent and total system

makes you feel really good.

- Temporally in a great order.

- Uh uh. - Absolutely.

- And I think that- - And I could tell you to me

is literally getting exposed to sun clearly in the morning,

clearly at noon, I go out,

I keep my windows in the office completely open,

eating mostly in the early time of the day and exercising.

And literally at the end part of the day,

I'm not really in a more thoughtful vegetative state.

Like I really can't like after 5:00, I tell my students,

if you want to tell me anything complicated,

you're wasting your time.

My brain just doesn't function.

So even though I only sleep at night,

but I'm really starting to shut off, ramp down.

Really I mean, I could send email,

talk about brainless stuff, but my power,

my energy to do powerful stuff really drop tremendously.

So all my students who know me very well,

they put the meetings with me early in the morning

'cause they know this is when I'm...

So, everything for me and for me, it's very tight.

So it could be different for...

It's very clustered in the morning.

It's all tied together.

And literally the remaining part

seems to be just a vegetative state.

- Mm hm.

Yeah, you and my bulldog, Costello,

who unfortunately passed away recently.

- Oh no. - Yeah.

- I did not, that's so sad. - Yeah, Samer and Costello

were good friends.

Yeah, sorry to break it to you here.

Yeah, he had a good long life and he went easy,

but he had a circadian clock that basically would just sleep

around 24 hours a day,

minimal activity interspersed every third day or so.

You do have this morning vigor.

- Yes. - And I think other people

are going to have more of an afternoon vigor.

Do you think that this can change across the lifespan?

The rumor is that teenagers naturally want to sleep in later

and stay up later.

Do you think that's social rhythm?

Or do you think that that's actually biological?

- Yeah, that's a tough question.

I mean, it could be both.

One thing that worries me is that it seems that if anything,

with age this morning rigor gets stronger.

- You mean, you want people to become more

of morning people. - More of morning people.

- Well, why does that worry you?

I think that's good.

- Because for me, I'm already very shifted morning.

I don't want to be one of these 7:00 p.m.

to 1:00 a.m. sleepers at some point.

- On the other hand, it's also kind of nice

because it's quiet and you can get work done.

- Yeah, but honestly from 4:30 till 7:30

when my wife wake up, it can be very long.

Yes, you achieved a lot, but it's quiet outside.

So, I don't want to be at 1:00 a.m., let's put it this way.

- You can tell Samer is more social than I am.

- That's right, that is true.

- But we should touch on that actually.

So, your wife, she follows a different schedule.

- Yeah. - So, the social rhythm-

- I'm honestly... - Is important I think.

What should we do?

How should we conceptualize and how should we adjust

ourselves according to the social rhythm?

- And I honestly love this hypothesis

that people came up with and Pat's kids reminded me of.

Because kids are really going to disrupt your sleep-wake cycle,

it seems like there is a chrono attraction.

That's usually people who attract each others

have actually different sleep-wake schedule.

And the idea being is that this allows them

to take care of their kids throughout the day-night cycle.

- And have a peaceful marriage.

- And have a peaceful marriage in a way, right?

So, I mean, we didn't have kids, me and Rejji.

So maybe this is, but it seems like evolutionary

it makes sense that if you want to protect your kids,

you don't want everybody to be morning vigor,

and then the kids don't have.

So you want it distributed across.

I mean, it makes sense. - It's a reasonable argument.

- Yeah. - I've heard that one

of the reasons that people think that the clock

is not exactly 24 hours,

but it's 24 hours plus or minus 20 minutes or so,

is because we believe that we evolved in clans or groups,

villages, whatever, that were about 100 to 200 people.

And in order to have protection around

the early morning hours- - Interesting, same idea.

- When we're vulnerable to predation

and in the late night hours,

that you would want some individuals of our species

to be naturally more like night owls

and some more like early people.

So your theory of parenting is similar in that way.

- Right. - The social rhythm

is a powerful rhythm though.

Meaning if I go out and I'm tired,

let's say I'm tired at like 9:30.

I don't want to go out, like I'm to need-

- So can I just say something about that?

I think the social rhythm is powerful at the obvious levels.

Like it affects your sleep,

it affects how much you wake up or eat,

but I'm not so sure it's as powerful as people think

on the clock.

Now, eventually it will mess up the clock

because now if you're doing a lot of social at night,

getting enough light, eating at the wrong time of the day,

eventually you're going to have an effect,

but I don't think just the social interactions themselves

have been shown to affect your clock very strongly

for some reason. - Yeah, that's good to know.

Well, for people hearing this,

they're probably getting the impression

like I'm the night owl, and then Samer is the one

that's in bed at 9:00 and then wakes up at 4:00.

But having attended many meetings with Samer,

I can tell you that he's the party animal.

So let's talk about that.

I mean, let's talk about the fact that you're the partier,

who's up until 2:00 dancing at these various meetings,

which I've seen. - Yep.

- He's actually a good dancer I'm told,

but what should we do when we do stay up very late,

for whatever reason; could be because we had

to take a midnight trip to the hospital,

an unfortunate reason,

or it could be because you're in the presence of people

that you don't see very often and you go out

for a really nice night out on the town and you get to sleep

around 2:30 or 3:00 in the morning.

How should one get back on schedule?

Do you force yourself to then get up and view light

at the normal time that you would get up and view light?

Or do you allow yourself to sleep in?

What what's the optimal protocol?

- I would allow myself to sleep in,

and remember this is a long-term effect.

This is something that you live with for a long period.

And remember I told you about the experiments

we did with the mood,

these required two weeks of that light schedule

to cause mood disturbances.

So these don't happen just in a single day.

- So this is the way you justify staying out late

every once in a while. - Well, in the meetings

you've seen me in,

I've done this for five or six days continuously,

but what you didn't see that when I came back to my home,

it took me two weeks as if I did a jet lag.

So I really do suffer for two weeks

after doing a six crazy night of staying up at night,

drinking at the wrong time of the day.

So it's not that I'm completely okay with it.

When I go back, everything goes back.

It takes me actually literally two weeks to recover

from the circadian rhythm meeting

that you've seen me partying at some point.

- Which is kind of ironic that the circadian rhythm-

- I know. - Meaning people are totally

disrupting their circadian cycle,

but scientists are human beings too.

- Right, so I think if you do it at very little occasions,

I think you should not worry too much

that this will have lasting impact.

And the good news is that if you readjust your schedule,

you could come back to it.

The problem is when you maintain this wrong schedule

for a prolonged time and it becomes chronic,

prolonged periods of time,

that's when you have the problems

and the accumulation of the problems.

So when you have sleeping problem,

you produce metabolic problem.

When you have metabolic problems,

you produce lack of exercise.

And you could see how things can spiral out very quickly.

And then it would be hard to come back to it.

- Well, certainly sleep disruption is both

a symptom of and- - Yes.

- A cause of almost all- - Absolutely.

- Mental health disorders. - Absolutely.

- And certainly the metabolic syndromes

that people are talking about nowadays and all of this,

it all funnels back to light.

This is what's so remarkable. - Eventually, yeah.

- And so we have these devices,

and I use my phone and I use my computer.

But do you think that the mere dimming of the screen

or not interacting with screens,

say 90 minutes or two hours before bedtime,

according to what we're saying today,

this should have a profound effect

on all these factors. - And it does.

And I really believe it does.

And, again, I think as Pat did these inventions

where you get a pouch where you put your phone in a pouch.

- Mm hm, so, what Samer's referring to is our friend, Pat,

this former Seal Team member,

who's also very impressive person in the landscape

of business and family, et cetera.

A real superhuman by any regard has this habit of taking

his phone and putting it into a sealed pouch

in the evening. - Yeah.

- So it's basically walled off-

- And in his program he sends you actually

these sealed pouches.

And so that I think is a great idea because not only

it will take away the light from you,

but it also take away the distraction

because you want to repair and recover, and sleep does that.

And if you have your phone dinging all the time,

or the light flashing from it,

you're just not getting enough sleep

and you're causing yourself major problems.

- I never asked you this, but I realized now

that I should have long ago, but I'll ask you now.

Why and how did you get into all this stuff?

- Yeah, I mean, honestly, first of all,

I wanted to study genetics and I knew

I wanted to do PhD in genetics.

But I only got accepted in one university at the time.

And I joined the Learning and Memory Lab.

And I liked learning and memory at the beginning,

I worked on the snails on Aplysia californica,

and started looking at learning and memory.

But then the same lab was looking at these daily variation.

I was really struck.

Like you never think about it outside of science.

It's really struck me that organisms

can measure day biologically.

That was very shocking to me.

And I just really got attracted and I wanted to see

why does this happen?

What is the effect of different times of day?

And I just stuck with it.

It just, it was mind blowing for me

who was in medical school,

that I've never heard about it before.

You know, it's really amazing medicine,

I think still now we are very good

at looking at stuff spatially,

but we're very bad at looking at temporal aspects.

So we always like to see images, static images,

spatial information.

- Right, take an x-ray, measure a temperature-

- Yeah, exactly. - Measure a blood pressure.

- But we don't think of temporal.

And you talk to John Hogenesch right now,

and he's telling you the importance of chronomedicine

or chromo pharma...

Whatever the word is.

And it really just getting the drugs

at the right time of the day is going to be essential

for our health.

- Do you think that's going to come from using better trackers,

like Oura rings, WHOOP straps, these kinds of things?

- I love the trackers,

but I think there's even more exciting discoveries.

Now you could take a single blood sample

and measure many biological components

and figure where you are in the circadian clock.

Something that was very hard to do before.

So if you have a marker to know where you are in the clock,

you could actually understand more the effect of everything;

exercise, feeding, light input.

- What is the marker?

- So there are some papers from what's her name?

Phyllis Zee and from Achim Kramer

where they measure multiple RNAs

that are known to tell you what phase of the clock is,

or multiple proteins or biological reactions.

And depending on a combination of factors,

not a single factor,

you could tell where you are in the circadian clock.

So they could instead of just measuring temperature

or melatonin, just one measurement.

And melatonin specifically, is also complicated by the fact

that melatonin is affected by light.

And temperature, your temperature and sleep can be

easily dissociable, right?

When you travel up those different timezone,

you sleep at different times in the temperature cycle.

So having multiple components measured will give you

a better determination of your circadian phase,

and understanding your circadian phase in humans

will telling you what is the effect of giving certain drugs

at certain times of the circadian phase.

So, in the future, this is going to be studied

at a much higher level when you can determine the phase

in relation to all the other stuff.

- It's striking to me that in all animals, besides humans,

if they deviate too much from the appropriate exposure

to light and light-dark cycle,

they essentially don't mate and/or die

and/or get killed off.

But in humans, we are able to override that at least

to some extent, but the ways in which we suffer appear to be

things like obesity, metabolic syndromes,

reproductive syndromes that are accompany

the other syndromes, you know, endocrine syndromes,

and mood and depressive disorders.

Is there any effort at the level of the nationally

or laboratories that you're aware of

to try and use light in order

to improve mood and mental health?

- I mean, honestly, this is my mantra.

This is the thing that I think people,

because I say, don't take a pill, take a photon.

And not, I mean, you take pills.

That's important.

I'm just making it that really we have an opportunity

right now with the incredible advances of LED lights,

of changing spectrum of light, of regulating intensities.

And just for simple changes,

you could really improve sleep-wake cycle, productivity,

and still you could actually get more done

because as we've talked about,

when you have all these messed up,

now you have to sleep more, but your sleep is fragmented.

It's not very good.

- And you can't focus when you do sit down-

- And you can't focus or you don't have alertness

when you need the alertness.

So having all these could allow you to do even more actually

at the end than less.

And that's the exciting part it.

- One of the questions I get asked most often about

is about ADHD.

I think there's a lot of self-prescribed

as well as clinically prescribed ADHD.

People are having a tremendously difficult time focusing

and not just because they're sleepy,

they just can't seem to anchor their attention.

And there could be multiple reasons for this,

but there are now several clinical trials ongoing

using light to try and anchor people's attention and mood

and wellbeing for sake of focus.

And I think that while I love this saying

that you mentioned, "Take a photon, not a pill."

And with due respect to the need for pharmacology

for some certain people,

I think most people just haven't really dialed in

their relationship to light in a way that allows them

to rule out whether or not they need medication.

- Absolutely, absolutely.

That's the best way to put it.

I can't add to that.

- Let's talk about jet lag. - Mm hm.

- But not in the context of, okay, if somebody's traveling

from Europe to Japan or from the east coast,

because that varies tremendously, right?

I mean, there's as many different variations

on travel as there are individuals out there with roles-

- Right. - And jobs, et cetera.

But rather, let's talk about what are the two

or three things that people can do

to adjust their schedule quickly?

Yesterday, I called you and said,

"Look, I know somebody who's traveling six hours.

I won't even mention in which direction,

'cause I don't want people to anchor to that example.

And you described some very simple tools of viewing light

a little bit earlier than normal

and getting on the local food schedule, et cetera,

that would allow them to shift more quickly.

- Exactly. - And the reason I want to

have this conversation is yes, for the travelers,

and for the shift workers,

but mostly because of the fact that you've proven

again and again that people are disrupted

in their circadian behavior at home.

So, aside from what we've already talked about,

how can one adjust quickly to a new schedule?

Like let's say, fall classes are starting,

you start a new job or you have a baby

or a puppy or whatever, what is the best way

to shift the clock quickly?

- So, it's very simple as we've talked yesterday.

So imagine you're in the outside with no industrial light.

If your body thinks you're in early evening

and you see a bright light, what does this tell you?

Oh, wait, this is not early evening yet.

It's still early afternoon or late afternoon.

So I have to delay my clock to go back to late afternoon.

So if you get light early in the evening,

it delays your clock.

So what does that- - Meaning that makes you

want to go to sleep later?

- Yes, it delays your clock.

So, you're in New York, right?

People in Italy have an advanced clock

because they are six hours ahead of us.

So if you're in New York and you get light early

in the evening, you delay even further from Italy.

So now you're delaying away from Italy.

Now the same thing happens.

Let's say, you thought dawn came up

and you thought it's already dawn,

but it was let's say three o'clock in the morning

or four o'clock in the morning.

And then you get to bright light and you say,

"Oh, wait a minute.

Dawn is not the up yet."

So I should advance my clock.

Or I'm at night, but I'm getting bright lights,

so I should run because dawn is already up.

So then later in the night, later in your night,

and actually it just happens that in humans

you get a temperature nadir later in the night,

low temperature in your body.

After that, lights start advancing your clock.

So if you want to go to Italy,

instead of getting light early in the evening,

you want to get light after the temperature low.

So you could advance your clock even before you go to Italy,

and you're catching up to the Italians just by using light.

It's as simple as that. - Great.

- So you could do it for every region.

You could calculate how much they are advanced of you.

You could know how much these light shifts happen per day,

and you can calculate what you need to do,

very simple math, to adjust either in direction of delaying

if you're going from New York to California,

you want to delay your clock

or advancing if you're going from New York to Italy.

- So, in order to make that a visual

and because a lot of people are listening to this,

not looking at it on video,

we will put a zero cost downloadable figure of this

on the HubermanLab.com website related to this episode.

But I think I can summarize it in language as well.

If I understand correctly,

what you're saying is if your typical wake up time

is say, 7:00 a.m., then your low point in temperature

probably occurs somewhere around 5:00 a.m..

- Yeah. - And if you view light

right around then it's going to essentially

advance your clock. - Yeah.

Because then your body thinks, oh, it's seven o'clock,

so advanced your clock by one to two hours.

- But if I were to view light, say at 3:00 a.m.,

then it would probably delay my clock?

- Yeah. - Okay.

Yeah, so, and then let's say I land in a new schedule.

I want to adjust to a new schedule.

Let's say I didn't manage to do anything

with my light viewing before I went.

And I didn't anticipate the trip.

Suddenly I'm on a new schedule, okay?

I was told that one of the ways to help shift the clock

and to avoid gastrointestinal issues

is to eat on the local schedule.

- Mm hm. - To start basically behaving

like a local. - Mm hm.

- Even though your circadian clock will take