Journal Club with Dr. Peter Attia | Effects of Light & Dark on Mental Health & Treatments for Cancer

welcome to the huberman Lab podcast

where we discuss science and

science-based tools for everyday

[Music]

life I'm Andrew huberman and I'm a

professor of neurobiology and

Opthalmology at Stanford school of

medicine today marks the second episode

in our Journal Club series with myself

and Dr Peter AA Dr Peter AA as many of

you know is a medical doctor who is a

world expert in all things Health span

and lifespan he is the author of the

bestselling book outlive as well as the

host of his own terrific podcast the

drive for today's episode Peter and I

each select a different paper to share

with you we selected these papers

because we feel they are both extremely

interesting and extremely actionable

first I present a paper that is about

how light exposure during the morning

and daytime as well as dark exposure at

night each have independent and positive

effects on Mental Health as well as the

ability to reduce the symptoms of many

different mental health disorders now

I've talked before on this podcast and

elsewhere about the key importance of

seeing morning sunlight as well as

trying to be in dim light at night

however the data presented in the paper

today really expands on that by

identifying the key importance of not

just morning sunlight but getting bright

light in one's eyes as much as is safely

possible throughout the entire day and a

separate additive effect of being in as

much Darkness at night as POS possible I

describe the data in a lot of detail

although you do not need a background in

biology in order to understand that

discussion and there's a key takeaway

which is that if you can't get enough

light in your eyes during the daytime

you would be well advised to get as much

Darkness exposure at night in other

words light and dark have independent

and additive effects on mental health

and during today's discussion you'll

learn exactly how to apply light

exposure and dark exposure in order to

get those benefits then then Peter

presents a paper about novel treatments

for cancer I must say it's an extremely

important conversation that everybody

regardless of whether or not you may

have had cancer or know somebody who's

had cancer ought to listen to he

highlights the current technology of

cancer treatments as well as the future

technology of cancer treatments and the

key role that the immune system and the

autoimmune system play in treatments for

cancer I assure you that by the end of

today's Journal Club episode you will

have learned

a ton of new information about light and

dark and mental health as well as cancer

and the immune system and treatments for

curing cancer before we begin I'd like

to emphasize that this podcast is

separate from my teaching and research

roles at Stanford it is however part of

my desire and effort to bring zero cost

to Consumer information about science

and science related tools to the general

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discussion with Dr Peter Atia Andrew

great to have you here for Journal Club

number two I'm already confident this is

going to become a regular for us I'm

excited I really enjoy this because I

get to pick papers I'm really excited

about I get to hear papers that you're

excited about and

we get to um sharpen our skills at

reading and sharing data and people

listening can do that as well so last

time I went first so uh I think I'm

going to put you on the hot seat first

and have uh have you go first and I'll

follow you okay well I'm really excited

about this paper um for a number of

reasons first of all it at least by my

read is a very powerful paper in the

sense that it

examined light exposure Behavior as well

as dark exposure behavior and that's

going to be an important point in more

than 85,000 people as part of this um

cohort in the UK um I'll just mention a

couple of things to give people

background and I'll keep this relatively

brief first of all there's a

longstanding interest in the

relationship between light and mental

health and physical health and we can

throw up

some very well agreed upon bullet points

first of all there is such a thing as

seasonal effect itive disorder it

doesn't just impact people living at

really Northern locations but basically

there's a correlation between day length

and mood and mental health such that for

many people not all but for many people

when days are longer in the spring and

summer they feel better they report

fewer depressive

symptoms and conversely when days are

shorter significantly more people report

feeling lower mood and affect Okay so

there's a long-standing treatment for

Seasonal effective disorder which is to

give people exposure to very bright

light especially in the

morning the way that that's normally

accomplished is with these sad lamps

Seasonal effective disorder lamps and

those lamps are basically bright meaning

more than 10,000 Lux lights that they

place on their kitchen counter or at

their table in the morning or in their

office so they're getting a lot of

bright light that is proven to be fairly

effective for the treatment of Seasonal

effective disorder what's less

understood is how light exposure in the

middle of the night can negatively

impact mood and health and so where we

are headed with this is that there seems

to be based on the conclusions of this

new study a powerful and

independent role of both daytime light

exposure and nighttime dark exposure for

mental health now a couple of other key

points the biological mechanisms for all

this are really well established there's

a set of cells in the neural retina

which aligns the back of your eye

they're sometimes called intrinsically

photosensitive retinal gangan cells

they're sometimes called melanopsin

retinal gangion cells we'll talk about

those in a bit of detail in a moment

it's well known that those cells are the

ones that respond to two different types

of light input not one but two different

types of light input and send

information to the hypothalamus where

your master circadian clock resides and

then your master circadian clock sends

out secretory signals so peptides

hormones but also neural signals to the

brain and body and say hey now it's

daytime now it's nighttime be awake be

asleep but it goes way beyond that these

melanops and intrinsically

photosensitive retinal gangling cells we

know also project areas of the brain

like the habenula which can trigger

negative affect negative mood they can

trigger the release of dopamine or the

suppression of dopamine the release of

serot in the suppression of do of

Serotonin and so they're not just cells

for setting your circadian clock they

also have a direct line literally one

synapse away into the structures of the

brain that we know powerfully control

mood so so the mechanistic basis for all

this is there so there's just a couple

of other key points to understand for

people to really be able to digest the

data in this paper

fully there are basically two types of

stimula that these cells respond to one

is very bright light as we just talked

about that's why getting a lot of

daytime sunlight is correlated with

elevated mood that's why looking at a

10,000 Lux artificial lamp can offset

Seasonal effective disorder by the way

just a couple questions on that um how

many Lux does the sun provide on a sunny

day at noon okay great question so if

you're out in the sun with no cloud

cover or minimal cloud cover in the

middle of the day at noon chances are

it's over 100,000

luck on a really bright day could be

300,000 Lux okay most indoor

environments even though they might seem

very bright I like to think of your

you're kind of like uh department store

with the bright lights believe it or not

that's probably only closer to 6,000 Lux

maximum and probably more like 4,000 Lux

most brightly lit indoor environments

are not that bright when it comes down

to Total Photon energy now here's the

interesting thing on a cloudy day when

you're

outside it can be as bright as or an

average of a 100,000 Lux but it won't

seem that bright because you don't quote

unquote see the Sun but it's also

because when there's cloud cover a lot

of those long wavelength of light such

as orange and red light aren't coming

through however and this is so important

the circadian clock the supermatic

nucleus it sums photons it's a photon

summing system so basically if you're

outside in 8,000 Lux very overcast UK

winter day and you're walking around

hopefully without sunglasses because

sunglasses are going to filter a lot of

those photons out your circadian clock

is summing the photons so it's an

integration mechanism it's not triggered

in a moment and actually the the

experiments of recording from these

cells first done by David buron at Brown

were you know historic in the field of

visual Neuroscience when shown bro

bright light on these intrinsically

photosensitive cells you could crank up

the intensity of the light and the

neurons would ramp up their membrane

potential and then start spiking firing

action potential long trains of action

potentials that have been shown to go on

for hours and so that's this signal

that's propagating into the whole brain

and body

okay so the the important thing to

understand is this is not a quick switch

that's why I suggest on non cloudy days

we'll call them that people get 10

minutes or so of sunlight in their eyes

in the early part of the day another 10

minimum in the later part of the day as

much sunlight in their eyes as they

safely can throughout the day but since

you're a physician I should just um and

you had a guest on talking about this

recently when the sun is low in the Sky

low solar angle sunlight that's really

the key time for we'll talk about in a

moment and when the sun is low in the

sky you run very very little risk of

inducing cataract by looking in the

general direction of the sun you should

still blink as needed to protect the

eyes it's when the sun is overhead and

there's all those photons coming in

quickly in one in a short period of time

that you do have to be concerned about

cataract and um macular degeneration if

you're getting too much daytime sunlight

so the idea is sunglasses in the middle

of the day are fine but you really

should avoid using them in the early and

later part of the day unless you're

driving into the Sun and you need you

know for safety reasons another question

Andrew if if a person is indoors but

they have large windows so they're

they're getting tons of sunlight into

their space they don't even need ambient

indoor light how much of the photons are

making it through the glass and how does

that compare to this effect yeah in

general unless the light is coming

directly through the

window most of the relevant wavelengths

are filtered out in other words if you

can't see the sun through the window

even if sufficient light is being

provided that's insufficient to trigger

this phenomenon that's right however if

you have um you know windows on your

roof which some people do skylights that

makes the situation much much better in

fact the neurons that in the eye that

signal to the circadian clock and these

mood centers in the brain reside mainly

in the bottom twoth thirs of the neural

retina and are responsible for looking

up basically they're Gathering light

from above

these cells are also very low resolution

so think of them as big pixels uh

they're not interested in patterns and

edges and movement they're interested in

how much ambient light there happens to

be now keep in mind that this mechanism

is perhaps the most well-conserved

mechanism in cellular organisms so there

and I'll use that as a way to frame up

the four types of light that one needs

to see every 24 hours for Optimal Health

and and when I say Optimal Health I

really mean mental health and physical

health but we're going to talk about

mental health mainly today in this

paper there's an absolutely beautiful

evolutionary story whereby single cell

organisms all the way to humans dogs

rabbits and everything in between have

at least two cone opson one that

responds to short wavelength light AKA

blue light and another one that responds

to longer wavelength light orange and

red so your dogs have this we have this

and it's a comparison mechanism in these

cells of the eye these neurons of the

eye they compare contrast between blues

and orange or sometimes blues and reds

and pinks which are also all long

wavelength

light there are two times of day when

the sky is enriched with Blues oranges

pinks and reds and that's low solar

angle sunlight at Sunrise and in the

evening these cells are uniquely

available to trigger the ex existence of

those wavelengths of light early in the

day and in the evening not in the middle

of the day so these cells have these two

cone photo pigments and they say how

much blue light is there how much red

light is there or orange light and the

subtraction between those two triggers

the signal for them to fire the signal

off to the circadian clock of the brain

and that's why I say look at low solar

angle sunlight early in the day what

that does is it what call it as phase

advances the clock this can get a little

Technical and we don't want to get too

technical here but think about pushing

your kid on a

swing the period of That Swing the

duration of That Swing is a little bit

longer than 12 hours okay so when you

stand closer to the kid so your kid

swings back and you give it a push

you're shortening the period right

you're not allowing the swing to come

all the way up that's what happens when

you look at morning sunlight you're

advancing your circadian clock translate

to English or non- nerd speake you're

making it such that you will want to go

to bed a little bit earlier and wake up

a little bit earlier the next

day in the evening when you view low

solar angle sunlight so in the a the

afternoon Setting Sun or evening Setting

Sun you do the exact opposite you're

phase delaying in the clock it's the

equivalent of your kid being at the very

top of the of the Ark and so it's gone

you know maybe 12 and a half hour uh 12

let's say 12 and a half hours is the

duration of that swing and you run up

and you push them from behind and give

them a little more push that's the

equivalent of making yourself stay up a

little later and wake up a little later

these two signals average so that your

clock stays stable You Don't Drift

meaning you're not waking up earlier

every single day or going to sleep later

every single day this is why it's

important to view low solar angle

sunlight in the morning and again in the

evening as often as possible and it's

done by that readout of those two photo

pigments now midday

sun which contains its bright light but

you see it as white light contains all

of those wavelengths at equal intensity

so the middle of the day is the

so-called circadian Dead Zone in the

middle of the day bright light triggers

the activation of the of the other opson

the melanopsin which increases mood

increases feelings of well-being has

some other consequences but you can't

shift your circadian clock by viewing

the sun in the middle of the day because

it's in the Circadian Dead Zone it's the

equivalent of pushing your kid on the

swing when they're at the bottom of the

Arc you can get a little bit more but

not much and in biological terms you get

nothing so this is why looking at

sunlight in the middle of the day is

great but it's not going to help anchor

your sleep wake cycle and if you think

about this is incredible right every

organism from single cells to us has

this mechanism to know when the sun is

rising and when the Sun is setting and

it's a color comparison mechanism which

tells us that actually color vision

Evolved first not for pattern Vision not

for seeing beautiful sunsets and

recognizing that's beautiful or

paintings or things of that sort but

rather for setting the circadian clock

now what if you only do one of these

Enders so what if you've got constant

exposure to low Morning Light but your

job prevents you from doing the same in

the evening or vice versa yeah a great

question better to get the Morning Light

because if if you have to pick between

low solar angle light earlier later in

the day and keep in mind if you miss a

day no big deal it's a slow integrative

mechanism average ing across the

previous two or 3 days but if you miss a

day you'll want to get twice as much

light in your eyes that next morning the

reason it's better to do in the morning

as opposed to the evening although both

would be to do uh best would be to do

both excuse me is that most people are

getting some artificial light exposure

in the evening anyway and here's the

Diabolical thing your retina is very

insensitive to light early in the day

you need a lot of photons to trigger

this mechanism early in the day as the

day goes on retinal sensitivity

increases and it takes very little light

to shift your circadian clock late in

the day keep in mind also that if you do

see afternoon and evening sunlight

there's a beautiful study published in

science science reports yes science

reports two years ago showing that that

can partially offset the negative

effects of artificial light exposure at

night I think of this as your Netflix

inoculation and the amount of melatonin

suppression from Nighttime light

exposure is haved by viewing even

Setting Sun now keep in mind you don't

need to see The Sun Cross The Horizon it

can just be when it's low solar angle so

you're looking for those yellow blue or

blue pink blue red contrast and on

cloudy days believe it or not they're

still there just you don't perceive as

much of it coming through so there

really so that's three things that we

should all strive to do view low solar

angle sunlight early in the day view

solar angle sunlight later in the day

and get as much bright light in our eyes

as we safely can ideally from sunlight

throughout the day

and if you can't do that get perhaps

invest in one of these uh sad lights

although they can be a bit expensive U

there are a couple companies that are

starting to design Sunrise simulators

and evening simulators that are actually

good that actually work um but right now

my read is that aside from one company

out there which by the way I have no

relationship to it's called the 20 light

tuo and that light bulb was developed by

the biologist at the University of

Washington who basically discover

covered these color opponent mechanisms

um those lights are not particularly

expensive but they're

um they do seem to work in fact they

they're the study that is emerging again

unpublished data seems to indicate that

if you look at it for more than five or

six minutes it can induce a mild

Euphoria that's how powerful this

contrast is and what they did there in

that light I'll just tell you the

mechanism is they figured out that when

most people look at low solar angle

sunlight in the morning they're getting

19 reversals of blue orange per second

so when you look at this light it looks

like a a barely flashing white light but

it's reversals of orange and blue orange

and um and you know red and blue and

it's happening so what what does the

person looking at it perceive um well

I've used one of these um it just looks

like a a flickering light and of course

there's the always the potential of a

placebo effect but well that's what I

was going to say is there a way to

control for that by having something

that looks the same to the user but of

course is not producing the same photo

effect yeah well they've done that with

the 10,000 Lux sad lamps and you and

which most people use to try and IND do

Sunrise simulation in their home but

keep in in mind that Sunrise is gives

you this comparison of short and long

wavelength light just a bright 10,000

Lux light triggers one of the options

that that but it won't set your

circadian clock so most of the sad lamps

that are out there are activating only

one of the mechanisms in these cells

that's relevant and not the one that's

most relevant so I'm excited about what

20 is doing I think that um and again I

have no relation to them except I know

the biologists who did the work that

that provide the mechanistic logic for

the that engineering I still think um

we're in the like the really like early

days of this stuff what should be done

is to have this stuff built into your

laptop right it should be built into

your phone and hopefully it will be now

I mentioned this color contrast thing in

sunrise and sunset I mentioned the

bright light throughout the day but

there's a fourth light stimulus that

turns out to be really important and

this will provide the segue into the

paper turns out that dark exposure at

night independent of light exposure

during the day is important for mental

health outcomes now most people think

dark exposure how do I think about that

well it is dark absence of light it's

the absence of light but what this paper

really drives home is that people who

make it a point to get dark exposure at

night aka the absence of light at night

actually benefit even if they're not

getting enough sunlight during the day

and this is especially true for people

with certain mental health issues so I

don't think we can overstate the value

of PR of accurately timed light exposure

to the eyes in the context of mental

health I think you know there's so much

data by now I will say however that some

people seem more resilient to these

light effects than others meaning some

people you know also don't suffer from

jet lag too much some people can stay up

late get a lot of bright light exposure

in the middle of the night and during

the day they got their sunglasses on all

day and they're in a great mood all the

time other people are more susceptible

these sorts of things and we don't know

whether or not gen polymorphisms underly

that I personally am very sensitive to

sunlight in the sense that if I don't

get enough sunlight I don't feel well

after a couple of days um but I'm less

sensitive to light exposure at night for

instance but I think it is

perhaps this is a big statement but is

perhaps the most

fundamental environmental stimulus for

levels of arousal and alertness which

correlate with all sorts of you know

neuromodulator and hormone outputs and

um so none of this should come as any

surprise I will mention one last thing

there was a study published gosh over 10

years ago now from Chuck iser Lab at

Harvard Medical School is a phenomenal

lab exploring circadian human health

behavior he's just considered a no pun a

luminary in the field but there wasn't a

study that was in error where they had

published in Science magazine that light

shown behind the knee could shift

circadian rhythms and that paper was

retracted um and a lot of people don't

know that it was retracted light

exposure to the eyes is what's relevant

here and as far as we know the color of

one's eyes like Darkness or lightness of

one's eyes Bears no relevance on their

sensitivity to these types of mechanisms

and on and on so so one question one

comment the question again is going back

to the morning evening light and I spend

a lot of time looking at those types of

skies for example just because of the

nature of my hobbies great right because

I'm always doing archery in the morning

and rucking in the afternoon so it's not

uncommon that I'm seeing both of those

how relevant is it that the Sun be above

the Horizon so for example um it begins

to get light about in 30 minutes before

sunrise and then you know right at so if

sunrises at

7:30 first light is is 7 and then you

know sort of 7:15 to 7 uh 30 is actually

quite bright I mean you can see anything

and everything and the same as true at

Sunset so does does that 30 minutes pre

or when sun is Beneath The Horizon

constitute part of that 10 minutes it

does I mean in an ideal circumstance

you'd get outside and see the sunrise

every day and you'd see the sunset every

day even on cloudy days some people like

myself wake up before the sun comes up

in which and I get this question all the

time well in the absence of powers to

make the sunrise faster which I'm not

aware anyone has certainly not me I

think the best thing to do is simply to

turn on as many Bright Lights as you can

indoors to trigger that melanopsin

mechanism if you want to be awake if you

want to stay asleep or sleepy then keep

them dim and then get outside once the

sun is starting to come out some people

wake up after the sun has risen right in

which case get what you can and some

people wake up 10 a.m. or noon in which

case you can still get the bright light

exposure but but you won't shift your

circadian clock now in the evening

especially in the winter months it's

important to look West and try and get

some sunlight in your eyes in the

evening if you've ever gone into the

clinic for instance at 2 o'clock in the

afternoon after lunch you know and then

in the winter and then come out and it's

dark when you're walk into your car it's

a kind of eerie feeling that sort of

eerie feeling May correlate with the

fact that you missed a signal your your

brain is trying to orient your brain and

body in time and that's what all of this

is right it's trying to orient in time

and again some people are more

susceptible to that than others some

people might like that um feeling of oh

I went in when it was bright and I come

out when it's dark but the vast majority

of people feel better when they're

getting this morning and evening

sunlight exposure and this is especially

important in kids all right this is one

of the things that you know this paper

points out and their good data that

people are spending approximately 90% of

their time indoors nowadays daytime time

time indoors and those indoor

environments are simply not bright

enough you think oh there's all these

bright lights and some people are

putting blue blockers on in the middle

of the day which is the worst thing you

could possibly do if you're going to

wear blue blockers and I don't think

they're necessary but if you're going to

wear them you'd want to wear them at

night and in the evening you don't need

to wear blue blockers you just simply

should dim the lights and ideally have

lights that are set a little bit lower

in your environment which the

Scandinavians have been doing for a long

time so you know kill the overhead

lights and don't obsess about bright

light exposure in the middle of the

night in fact for a long time I and some

other people were saying oh you know

even just a brief flash of light in the

middle of the night can you quash your

melatonin that's true but the other time

in which you're in the quote unquote

circadian dead zone is in the middle of

the night you can't shift your circadian

clock in the middle of the night but you

know all of this gets down to inter

weaving rhythms of light sensitivity

temperature hormone output cortisol it I

mean there's a whole landscape of

circadian biology this paper um which

was published in a new Journal I'm

really excited about called nature

mental health this journal was just

launched recently uh is entitled day and

night light exposure are associated with

psychiatric disorders and objective

light study in more than 85,000 people

now I have to say that I think the title

of this paper is terrible sorry folks at

nature mental health because if one just

read the title it sounds like day and

night light exposure associated with

psychiatric disorders right if this were

If This Were a newspaper headline You'

be like oh my goodness well what are you

supposed to do right but that's not the

conclusion the conclusion is that

getting a lot of sunlight exposure

during the day and getting a lot of dark

exposure at night is immensely

beneficial for psychiatric health and in

a number of ways now I'm not one to

bring up another paper unannounced but I

will say that this paper built off a

previous study entitled time spent in

outdoor light is associated with mood

sleep and circadian rhythm related

outcomes and that was a cross-sectional

longitudinal study in

400,000 biobank participants so this UK

biobank is an incredibly valuable

resource and there are now multiple

studies establishing that one's pattern

of light exposure is extremely important

now the previous study in

400,000 participants basically nailed

home the idea that the more time you

spend Outdoors

the better your is your mood the better

is your sleep the better is the

rhythmicity of your sleep wake cycles

and on and on something that I think

even though people will say we've known

that for thousands of years needed

scientific

substantiation this new study

essentially looked at the relative

contributions of daytime light exposure

and nighttime dark exposure and they did

that on a background of it looking in

particular at people who had major

depressive disorder generalized anxiety

PT SD bipolar

disorder he here's the the basic

takeaway and I'll I'll quote them here

and then I'll I'll tell you my

interpretation that here I'm quoting

avoiding night at light and seeking

light during the day I love that word

seeking may be a simple and effective

non-pharmacologic means for broadly

improving mental health so that's a

pretty bold statement right and I love

that they say seeking because it implies

that people aren't reflexively getting

the light exposure that they need that

this needs to be a practice ice much

like Zone 2 cardio or resistance

training okay so so what did they do in

this study so basically they gathered up

100,000 people or so it eventually was

paired down to about 86,000 participants

because some just didn't qualify or

didn't report their data back they

equipped them with accelerometers on

their wrist and those wrist devices also

could measure ambient light now that's

not a perfect tool because what you'd

love to do is measure ambient light at

the level the Eyes by the way will

somebody design an eyeglass frame that

changes color when you've gotten

sufficient light from sunlight during

the day and then and then at night is a

different color and then if you're

getting too much light exposure will go

to a different color frame this has to

be possible so that you don't have to

wonder if you got enough light during

the

day and of course if it's at the level

of the eyes then you know that's what's

landing at the eyes yeah and it's l i

mean that's what I was going to ask you

about that do these wrist based devices

potentially get covered by clothing and

some like turned you have your sleeves

down I have my sleeves up they had it on

the outside of the sleeve but they asked

that people just keep it on their

dominant hand it's not perfect but in

some ways it's kind of nice that it's

not perfect we could turn that

disadvantage into an advantage by

thinking you know when the person is out

and about they're not often looking

right at the sun you know if you're

talking to a colleague under an overhang

for instance so it's it's not perfect

directionally it's directionally right

okay and then they had two hypotheses

two primary hypotheses one that greater

light exposure in the day is associated

with lower risk for psychiatric

disorders and two second hypotheses

greater light exposure at night is

associated with higher risk for

psychiatric disorders and poorer mood

this is oh so relevant for the way we

live now people on screens and tablets

in the middle of the night okay then

they collected information about how

much light exposure people were getting

as well as their sleep and their

activity and so on I should mention this

was done in males and females it was a

slightly older cohort than one is used

to seeing people in their 50s and 60s

they had psychiatric diagnosis

information and then they divided people

into essentially two groups but they had

a lower so a q1 and a Q2 a lower cortile

that meant people that were getting less

daytime light as opposed to the third

and fourth quartile more daytime light

they also had a nighttime light

exposure evaluation and they had people

were in the low q1 and Q2 so these

people are getting less nighttime life

light versus Q3 Q4 more nighttime light

nicely they also looked at sleep

duration and they looked at photo period

meaning how long the days were for those

individuals how active they were what 10

hours a day 14 hours a day because the

more active you are the more opportunity

for light exposure you have during the

day or night for instance okay so it

they had I would say fairly complete

data sets then and I'm just going to

kind hit the top Contour of what they

did in each and sorry sleep duration

sleep efficiency Etc was determined off

the accelerometer that's right as well

as self-report yeah not not ideal right

you'd love for people to be wearing a

woop bander or or a ring or something of

that sort but this was initiated some

time ago so um they either didn't have

access to that technology or for

whatever reason didn't select

it I'd like to take a brief moment and

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huberman then what they did is they got

they have information on who has major

depressive disorder who has PTSD

generalized bipolar psychosis Etc and

then they ran three models and you can

tell me what you think about the power

of these models but you know as somebody

who thinks about the mechanistic aspect

of all of this a lot but not somebody

who's ever run this type of study I'd be

really curious model one examined the

unadjusted association between day and

nighttime light exposure and psychiatric

outcome so just basically asking is

there a relationship between how much

light you get it during during the day

and how much light you get at night and

how bad your or your depression is or

anxiety is ETC looking at you know just

a standard ratio of the probability that

you have a certain symptom or set of

symptoms versus you don't given a

certain amount of light exposure model

two adjusted for the age of the person

their sex and

ethnicity and photo period so they

looked at you know how long the days

were in that given person's region of

the

world and then model three these people

were all in the UK or were they around

the world they were all in the UK as far

as I know and then model three adjusted

for employment so employed versus

unemployed which if you think about it

is pretty important like you say well an

unemployed person has a lot more time to

control these variables but an employed

person who's doing shift work does not

right and they they Incorporated

information about employed versus

unemployed physical activity which turns

out to be very important and then things

like shift work etc and so these what

what we can say very safely is that the

outcomes with each of these models the

results were very similar so we don't

want to discard the differences between

those models entirely but in my read is

in every figure of the paper it doesn't

seem like model one two or three differ

from one another in terms of total

outcome yeah that's an unusual aspect of

this paper so so these adjustments are

very standard right so that's this is a

a classic uh tool that's used in most

epidemiology um because you don't have

randomization so once randomization is

out the window you know you you're like

so for example the paper I'm going to

present is based on an RCT there will be

no models it's just he the data right

yeah here they're asking people what

what do you do report back to us we're

going to measure your light exposure but

no one was assigned to any groups they

swapped there the the whatever quote

unquote controls are

there they're really not there it's just

comparisons between groups so what is

interesting to me uh is that as it's

exactly as you said and we'll make all

these figures available in addition to

the papers but um I mean there it's very

unusual that there's no difference

between the unadjusted and the adjusted

models and as you say there's probably

two places out of you know 30 when you

look at all the different quartile

comparisons where you might Creep from

you know statistically significant just

out of it or just into it but yeah you

could simplify this figure two

completely by just showing one of the

models and you would be you know getting

95% of the information which is you know

I mean I think in one way that

suggests that there's less dependency on

those

variables of course it still doesn't

address probably the greatest question

question I have here which I'm sure

we'll get to at some point as as you

continue yeah so I'm very curious what

that question is but I'll I'll I'll

suppress my curiosity for the moment you

know so if we look at figure two of this

paper and I realize a lot of people are

listening and and they're not able to

look at this although we have posted the

figures on the YouTube versions of this

uh just want to make clear what's going

on just for those that are listening

essentially what they're looking at is

what they call the odds ratio which is

the probability of something happening

in one group vers divided by the

probability of something happening in

another group I guess would it by way of

example be you know if you're going to

look at the odds ratio of you know the

probability of somebody getting lung

cancer if they smoke versus probability

somebody getting lung cancer if they

don't smoke so odds ratios and Hazard

ratios are often confused they're very

similar and odds ratios generally refer

to a lifetime exposure whereas a hazard

ratio is um defined over a specific

period of time but the MTH is still

effectively the same and uh using the

example you gave if you took the odds

ratio of um you know death so let's talk

all cause mortality for a smoker versus

a nonsmoker and the answer were 1.78 I'm

making that up but that's directionally

correct 1.78 as an odds ratio means

there's a

78% chance greater of the outcome of

interest in this case death by any cause

in the affected Group which would be the

smokers so odds ratio of two is 100% and

odds ratio of three is 200% so the math

is take the number subtract one and

that's the percent you know figure two

of this paper is one of the key

take-homes they essentially look at the

odds ratio of people who are in the

let's say that let's just look at the

nighttime light exposure and just remind

me Andrew CU and and everybody else

watching the every one of these is

showing second third fourth as your

x-axis meaning they're all being

compared to the first quartile that's

right and the first quartile is lowest

light exposure or highest light exposure

low well or well we have to um

differentiate between day and night

that's right okay so restate it sure so

uh if we look at you know what is your

risk of a psychiatric challenge broadly

speaking well panel a is is major

depressive disorder if you are in the

second quartile third quartile or fourth

quartile of nighttime light exposure so

second being the least amount of

nighttime light exposure third being

more nighttime light exposure and fourth

the most nighttime light exposure

relative to the first quartile this is

just a stupid thing like if I were doing

this figure if you were doing this in a

lecture you know what you would do to

make it so easy you would draw arrows on

it that say increasing light exposure at

night decreasing light exposure in the

day it's the same information it just

makes it easier for the reader to

understand absolutely but and maybe the

teaching point I think is is for people

when they review articles like don't be

afraid to do that and just kind of like

oh I've got all over this exactly so

it's like I I draw the arrow that's

increasing light that's decreasing light

and that's how I can pay attention to

what's actually happening right and I'm

actually in touch with the editorial

staff at nature at nature mental health

although they don't know that I'm

covering this paper until after this

comes out you know I think one thing

that scientific journals really really

need to do is start making the

readability of the Articles better for

nonex experts I mean chances are if you

can't understand a graph and this is

true for everybody chances are there's a

problem with the way it's presented yeah

put it on them but then of course try

and parse it because um you know rarely

if ever is it all spelled out clearly

but anyway that's what we're trying to

do here so yeah the way I would have

done is say second quartiles low amounts

of nighttime light exposure and Define

what that is you

know third quartile is more light

exposure and then fourth maximum amount

of light exposure at night and basically

what you see is that the probability of

having worse major depressive symptoms

linearly increases as you go from the

second to third to Fourth quartile so

more nighttime light exposure worse for

you and there's a dose response if you

will of the effect now we can March

through or describe figure two pretty

quickly by saying the same thing is true

now just talking about nighttime light

exposure for generalized anxiety

disorder so that's panel C bipolar

disorder although the difference between

the second and the third quartile in

bipolar disorder isn't as traumatic once

you get up to the fourth quartile

bipolar symptoms get much worse when

people are getting nighttime light

exposure I really want to emphasize that

point because they go on in the

discussion of this paper to reemphasize

that point several times in fact they

say that while light EXP exposure during

the day of course we will go into the

data is beneficial for mental health for

people with bipolar disorder it seems

that light exposure at night is

especially problematic independent of

how much sunlight they're getting during

the day so your bipolar um in the person

with bipolar disorder who's struggling

with either a manic or a depressive

episode who's making a point to get

sunlight during the day who's also

getting light exposure at night is

making their symptoms worse and keep in

mind they they couldn't completely

control this but is largely independent

of things like sleep duration so that

doesn't necessarily mean that the

person's sleeping less although in a in

a manic episode presumably they are it's

independent of exercise it's independent

of a bunch of other things because any

any logical person will hear this and

say okay well they're they G more light

at night because they're doing a bunch

of other things but it's largely

independent of those other things

likewise the symptomology of PTSD gets

far worse with increasing light exposure

at night

self harm really takes a a leap from

being fairly I don't want to say minimal

at the second and third quartile so low

and let's say medium I'm using some I'm

taking some Liberties here but low in

medium amounts of of artificial light

exposure at night than for people who

get quite a lot of nighttime light

exposure self harm goes up and

probability of Psych psychotic episodes

goes up or psychotic symptoms now what's

nice is that the

what's nice about the data is that the

exact inverse is basically true for

daytime light exposure although not

across the board we can generally say

that for major depressive disorder

generalized anxiety bipolar symptoms

there it's a little more scattered PTSD

and self harm the more daytime light

exposure ideally from sunlight because

that's actually what's being measured in

most cases we could talk about how we

know

that is going to approximately linearly

drop the probability or the severity of

these symptoms and we could just explain

again that the odds ratios now seem to

be going down so an odds ratio of 7 now

refers to a 30% reduction in the

variable of interest here exactly now

the The psychosis panel F which uh

focuses on psychosis I think is also

worth

mentioning in in a bit more detail

there's a fairly dramatic reduction in

psychotic symptoms as one gets more

daytime light exposure independent of

nighttime light

exposure there's a well-known phenomenon

called ICU psychosis which is that

people come into the hospital for a

broken leg or a car accident maybe they

were getting surgery from from Peter

back when for something totally

independent they're they're housed in

the hospital and as anyone who's ever

been in a hospital as a patient or

visitor knows the light in the lighting

environment of the hospital is

absolutely dreadful for health just

Dreadful I mean people often complain

about the food in the cafeteria as being

unhealthy that's often not always

true not always true but the lighting

environments in hospitals is absolutely

counter especially especially in the

Intensive Care Unit yeah right I think

the the Intensive Care Unit at Hopkins

the main one the the main sucku didn't

have Windows people who who go into the

hospital with with a brain injury or or

with a stroke or something I get

contacted all the time even though I'm

not a clinician what should I do for my

kid my parent my I say get them near a

window and start to the best of your

abilities controlling their sleep wake

cycle now often times there's there you

know nurses coming in and taking blood

tests and measuring pulses in the middle

of the night that's disruptive there

there's bright light not just blue light

that's disruptive it's noisy that's

disruptive ICU psychosis is when non

psychotic individuals start having

psychotic episodes in the hospital

because of nighttime light exposure and

in some cases lack of daytime

sunlight we can can say that with some

degree of confidence because when those

people go home even though sometimes

their symptoms for what brought them to

the hospital in the first place get

worse their psychosis goes away now and

it's independent of medication so let's

just be really

direct there is a possibility that we

are all socially jetlagged that we are

all disrupting these mood regulation

symptoms systems excuse me by not

getting enough daytime light and by

getting too much nighttime light if we

want to look at just some of the bullet

points of the takeaways and then Peter

thank you you highlighted a few of these

but can we just go back to this figure

two for a second there's a handful of

things that really was going to want to

want to dig in the DAT just um and and

again I normally wouldn't make so much

hay out of this except for the fact that

they're so tight um but the there are a

few that really stand out um and again I

love this figure um I would have labeled

it a little differently to make it

completely userfriendly but nevertheless

the increasing light at night and the

impact on

depression let let me be really

technical in what I say and the

relationship or correlation to

depression is very strong um the

relationship to light and self harm in

the upper cortile so when you take those

25% of people with the most nighttime

light that relationship to self harm is

interesting and completely uncoupled

from the other 75% that's interesting

but uncoupled you mean that at the lower

levels of light exposure at night you're

not seeing an increase in self harm not

what and then once you get to that

fourth quartile it's a big step it's

like a 30% greater risk of self yeah so

it's totally flat the first second third

quartile no different and then fourth

big jump um and then the the the inverse

relationship right as light increases

during the daytime you see this

reduction in self harm interesting the

PTSD relationship based on nighttime

light and The psychosis relationship

based on daytime light those are the

ones that really jumped out to me uh I

think anxiety

relatively the you know less impressive

here and and bipolar disorder didn't

seem as strong right as well so I think

those those are the big ones that that

jumped out to me yeah I agree there's

AIT there's a bit more scatter on

generalized anxiety and and the degree

of the sign the degree of significant

change is not is not as robust in other

words getting a lot of daytime light

ideally from sunlight is not necessarily

going to reduce your levels of anxiety

getting a lot of nighttime light

exposure is not increasing nighttime

anxiety that much although 20% you know

is is not nothing um for nighttime light

exposure but yeah where the psychosis

major major depression and self harm are

really you know they leap out actually

we maybe we even just drill a little bit

deeper on major depression basically

when you go from the second to third

quartile of nighttime light exposure so

more than nighttime light exposure you

basically go from no significant

increase to almost almost a 20% increase

and then as you get up to the fourth

quartile so the most nighttime light

exposure you're at about

25% increase in major depressive

symptoms not that's no joke um and you

know and I think that I think that we

you know if we were to uh know we don't

have the data right here but if we were

to look at like standard SSRI treatment

for major depression you know um people

debate this pretty actively but um light

is is a very potent stimulus and the

timing of light is critical because on

the the inverse is also true as you get

to the fourth quartile of daytime light

exposure you get about a 20% reduction

in major depressive disorder what I like

about a study like this is that it puts

the error bars so easy to see on the

data and why is that interesting well um

there's there's um there's a there's a

belief that bigger is always better in

sample size and we often talk about that

through the lens of power analysis right

so how many subjects do we need to um to

to reach a conclusion that is powered to

you know this level and that's that's

true but what I don't think gets

discussed as often is the opposite of

that which is what if you overpower a

study in other words what if the power

analysis says to be uh to have a level

of power at 90% you need a th000

subjects and you Sayre we're going to do

10,000 subjects well you're clearly

powered for it but you might be

overpowered and people might say well

why would that be a bad thing it could

be a bad thing because it means you are

very likely to reach statistical

significance in things that might not be

actually significant and so one thing

about this study that is just a quick

back like kind of a quick and dirty way

to tell that it's probably not

overpowered is that you have varying

lengths of error bars and what that

tells me is that and again this is not

like a formal statistical analysis it's

just kind of like a back of the envelope

statistical analysis if you look for

example at self harm in the top quartile

you actually have pretty big error bars

in fact all the self harm have sort of

slightly bigger error bars and yet when

you look at for example the depression

even though the a bars aren't all the

same size they're tighter in fact when

you look at the relationship between

depression and daytime light the air

bars are really really small so that

just gives me confidence that there is

variability in this which paradoxically

you kind of want to see because it tells

me that this wasn't just done you know

there was I think you said 8,000

subjects were in this and I realized 8

more than 86,000 86,000 sorry yeah you

realize that it wasn't that oh this

should have been done with a tenth of

that or a half of that and we're picking

up um signal that is statistically

relevant but clinically irrelevant yeah

thanks for for that point that I didn't

pay attention to that um I mean I paid

attention to the air bars but I didn't

know that um so thank you I'm learning

too and I I suppose for people that are

listening we can just give them a sense

of what the error bar ranges are for

self harm you know they're running you

know as much as 20% either side of the

the mean the average and for major

depression it looks like it's more like

let's say 8 to 10% if if that if that

maybe like five right so um yeah I see

what you're saying so when you get a a a

very large sample size you're going to

have some outliers in there and you can

mask those outliers just by having so

many data points right yeah because

these error bars directly tell you

whether or not your statistically

significant so what's really nice about

this type of graph and you see these in

there's going to be a graph in my paper

where you see the same analysis um

they're always drawing the 95%

confidence interval on the on the data

point and if the 95% confidence interval

does not touch the the line of unity

which in this case is the the the the

hods ratio of 1.0 or the x-axis then you

know it's statistically significant to

the confidence interval they've defined

which is almost assuredly 95% sometimes

they'll make it tighter at 99 and so

that's why you can just look right at

these and go oh look you know in

depression the second quartile didn't

reach statistical significance because

the error bars are touching the line

just as the case for the second and

third quartile for self harm but when

you look at the fourth quartile you can

see that the lower tip of the error bars

isn't anywhere near Unity and so we know

without having to look up the P value

that it's uh smaller than either 05 or

0.1 however they've defined it and it's

really amazing when you see these you

know overpowered studies which are

easier to do epidemiologically where you

know the P value ends up being

microscopic you know they can they can

drive their P values down to anything

low because sample size can be infinite

but you know you can see that it's just

like the the error bar is just skimming

above the uh the the unity line but it's

so so so tight I'd like to take a quick

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huberman one thing that I hope people

are taking away from this study is that

imagine you're somebody who has a very

sensitive circadian mood system well

that would mean you need less daytime

light exposure to feel good or less bad

but it also means that you might need

very little light at night in order to

negatively impact your mood systems and

in fact they make this argument in the

discussion as an interesting point that

I think is worth mentioning what because

here what I again what I like about the

study is that they've separated day and

nighttime light

exposure turns out that many of the

drugs that are used to treat bipolar

disorder reduce the Sens are are

effective perhaps in part because they

reduce the sensitivity of the light

sensing circadian apparati now that's

interesting right if if you think about

this okay so these are drugs that can

ameliorate some of the symptoms of

bipolar perhaps in part by reducing the

extent to which nighttime light exposure

can relieve bipolar symptoms can excuse

me can exacerbate bipolar

symptoms conversely there's evidence

that people who take take certain

anti-depressants May suppress the

ability for daytime light to positively

impact the mood systems of the brain now

of course we don't want people halting

their medication on the basis of that

statement alone please don't you know

talk to your psychiatrist but if we know

one thing for sure it's that if you want

a significant outcome and a paper as a

scientist give a drug any drug and look

at the amount of rapid eye movement

sleep or the Circadian cycle pretty much

any drug Alters the Circadian

rhythm for better or worse but if we

start to think about which medications

might adjust our overall sensitivity to

light sometimes this could be a good

thing you think less sensitivity to

light well for people who have bipolar

disorder the amount of daytime light

exposure isn't that important for their

overall mood regulation but the amount

of nighttime light exposure really is in

other words Darkness for eight hours

every night should be viewed in my

opinion as a treatment for bipolar

disorder not the only treatment but it's

also clear that we should all be

avoiding really bright extensive really

bright nighttime light exposure I mean

if if anything you know my take away

from this study is that Darkness at

night is the fourth key light stimulus

now a couple of things very bright

Moonlight very bright candle light is

probably only

like gosh three to 50 lucks what when

you go outside on a brightly lit full

moon night I encourage people to

download this free app I have no

relationship to it called light meter

and it gives you a pretty good read of

what the lucks are in that environment

by the way a lot of people don't realize

this they think you just tap the button

and then it tells you how many lucks you

hold it down it's kind of fun you can

scan around the room and see how many

lucks are on average coming from that

location or outside go out on a really

bright moonl night I mean we we should

have a full moon tonight yeah let's do

it you're not going to get above a 100

Lux that's incredible you're sitting at

a candlelight dinner with your spouse or

with friends and it's clearly bright

enough to see them put that lux meter

right up not too close to the flame 50

to 200 Lux i i 4 interesting experience

a couple of months ago on an elk hunt

where it was a full moon which actually

makes the hunting not so great but it

was the first time I've ever noticed my

shadow in relation to the Moon uh that's

how bright it seemed the light was this

is Halloween appropriate since we're

coming out we we're recording this close

to Halloween it's remarkable super

interesting to think it could be that

dim campfire you know and Fire Light you

think okay gathering around a campfire

then okay you know everyone circadian

rhythm must have been disrupted for ages

before the development of of electric

electricity no no that th those

campfires are extremely bright but

they're they're they're not they're not

that bright compared to a very densely

overcast day and what is is your phone

if you don't use any sort of uh light

mitigating uh Tech on it well distance

matters um at the distance we're holding

it yeah with so with all the the

wavelengths cranked up so no uh there is

a nice feature intrinsic to the phone

where you can eliminate the blues at

night or you know this kind of thing but

if you crank it up to maximum light

intensity probably something like you

know 500 to 1,000 Lux now keep in mind

though it's additive right so it's over

time so Lux is a measure of I think I

think it relates back to Candelas it's

the amount of light um shown at I think

it's like the the one meter away and

there's a squaring and a falling off of

distance we can look it up um these are

old measurement old school measurements

converted to Lux but keep in mind that

if you're looking at your phone or

tablet at 800 Lux or 500 Lux in the

evening you do that for 2 hours well

you're summing quite a lot of photons

now it is true and I I I I do want to be

fair to the biology uh and it'd be

dishonest to say anything different you

know we we've hammered on people about

not shifting their circadian rhythm with

light at night but we know that the

middle of the day and the middle of the

night are circadian dead zones you can't

shift your circadian rhythm that well in

the middle of the day and the middle of

the night but you can provide a wakeup

signal for for your body and brain it's

really that sunrise and sunset that are

critical that's why I said there are

four things see sunrise or sunrising you

don't need to see across the Horizon

Sunset bright light during the day

minimize light exposure at night and you

don't need Pitch Black in fact pitch

black probably just increases the

frequency of injury you know I get up in

the middle of the night to use the

bathroom probably once I think it's

normal I go back to sleep you know if it

were pitch black I'd probably injure

myself so just just dim it down some

people use red lights you know our

friend Rick Ruben yeah Rick ruin is uh

can we tell a funny story about Rick

yeah of course of course you know this

story but just I just in casee Rick's

listening he'll appreciate this you know

when Rick was uh here staying last

summer um he's up in our guest house and

he came down after the first night and

he was like unacceptable you know what

I'm talking about unacceptable

accommodations what did he do he removed

all the lighting that existed in that

room and replaced it with red light

bulbs which I later used when I stayed

here and then later stole when I

left the teenage me I took them I took

him that's why Derek when he stayed here

lane or anyone else when he stayed here

Cony or anyone else didn't have those I

took them I love them so funny Jill is

like you know Rick changed every light

in the guest house to Red I'm like yeah

no I didn't know that but I'm not

surprised yeah well in his place he has

mostly either no lighting or red

lighting so during the day he just goes

by ambient light um and then red light

in the evening and or candle light and

it's great and you know people hear red

lights and they think they have to buy

these expensive red light units that's

not what we're talking about that you

can literally buy red party lights or

just a red bulb some people say well can

I just use a red film or can I put a

t-shirt over the lamp I worry about

people putting t-shirts over lamp

because of the fire hazard um but I'll

be honest I dim the lights in my home at

night um when I travel sometimes I will

bring one of the the stolen from Rick

Rubin red lights the red the Rick rubben

stash here's something where I've I've

sort of softened my tune so I used to be

kind of a hard liner no blue light in

the evening guy um you know had the you

know everything was red light at night

as far as my phone using flux on the

computer you know whatever it was

um I suspect that that matters somewhat

but I think what matters more is the

stimulation that may come from those

things and what I've come to realize at

least in me which means it probably is

true in others as well and at least some

others is that what I'm doing on my

phone matters more than how how bright

my phone is in other words if I've got

the best blue light filter in the world

on my phone but I'm doom scrolling

social media and getting lit up on email

that's way worse for me than if I've got

my phone on maximum light and I'm like

watching YouTube videos of F1 cars and

driving around having fun like it's a

totally different experience so so so

the context matters and um I think I

think for that reason I I I would want

people to be mindful of the whole

picture um you know going to bed under a

period of you know intense duress

brought on by something you know that's

an equally dangerous component to all of

this that's that's distinct from what

we're talking about but but you know you

just want i' like I want people to be

able to think of this in the context of

everything yeah I it's a really

important point you know one thing I'll

say is that if you're going to stay up

past your normal bedtime if you're going

to get a lot of light in your eyes I

would hope that it would be for fun

reasons and for reasons you enjoy you

should definitely spend some nights out

you should definitely do some all

nighters studying if you really you know

if you if it's going to help you get the

grade that's permanent right I'd

certainly have done all nighter studying

and grant writing for years um you know

there are going to be the inevitable

allnighters due to God forbid a Hos trip

to the hospital or you heard something

on the news that really amped you up or

you just simply can't sleep that stuff

is going to happen so I think the goal

should be to minimize light exposure at

night and I think what you just said is

especially true because we don't know

for instance people talk about the

negative impact of social media is it

the fact that people are looking at this

little box for so many hours per day is

it all the things they're not doing is

it what they're looking at per se all of

those things interact and are really

important I we know based on studies

from the Stanford sleep lab that if you

wake up in the middle of the night

looking at what time it is can be very

disruptive to your ability to fall back

asleep and to your sense the next day

it's just a placebo effect but it's a

powerful one of how tired you are the

next day they've done this where they

wake people up in the middle of the

night and then they say it's you know

4:00 a.m. versus 2: a.m. versus 6:00

a.m. and people's perceived levels of

energy during the day in some ways

correlate with what they think how much

sleep they think they got likewise and

this is one of the concerns potential

concerns with sleep trackers yep Ali

Crum talked about this when she came on

our podcast you know if people see a

poor sleep score they often feel worse

than if they see a good sleep score now

of course physiology matters you can't

lie to yourself and say you you know got

a great night of sleep simply by virtue

of a sleep score but I worry more about

the the

false well I if it's a false negative

that we don't want to put veilance on

this seeing a bad sleep score and then

deciding that you're going to have a

terrible day you know I think a bad

sleep score is an indication that you

might need to dial some things in a bit

better getting a great sleep score is an

indication that you might be doing a

number of things right and start looking

at these things as averaging wouldn't

would you agree yeah completely I I I I

don't think it's that different from CGM

right like I think that CGM is an

amazing tool to provide insight and you

pretty much know the insights after a

relatively short period of time 30 days

maybe at the outside 90 for for a really

per for a person with a very complicated

life um and you know all you need to

know about how the inputs affect the

output thereafter if you choose to use

it it's a behavioral tool in other words

you're using this to build in a Hawthorn

effect I think the same is largely true

with sleep trackers um most people have

this profound sense of learning when

they first encounter one of these things

and and it's again you've heard it all

100 times oh my God I can't believe what

alcohol does to my sleep right or

caloric trackers exactly like I think a

lane Norton's app carbon I have no

Financial relationship to it I use it or

and it's taught me wow like I consume a

lot of calories in the form of certain

things at certain times of day and

there's just a lot of good learning in

that but it's the Act of tracking that

helps you manage it and similarly I

think it's the act of knowing you're

going to be looking at that score that

gamifies it that kind of helps people do

the right things oh you know what I'm

not going to have that drink tonight or

I'm not going to eat that snack before

bed because I've now been conditioned to

see how that impact score that said I

think that um you know recovery scores

and things like that are just

notoriously poor at predicting

performance and I think there's a reason

that serious athletes would never use

things like that um they would tend to

rely on the more tried and true methods

of predicting Behavior such as heart

rate uh maybe heart rate variability but

morning resting heart rate probably more

predictive than anything else and then

you know inw workout things such as

heart rate heart rate recovery lactate

threshold things like that so yeah I

agree I think we have to and I say this

as a guy who's generally perceived to be

the most Pro device guy in the world

people would be surprised how sparingly

I use things like that

I mean I do some Tracking not as much as

you uh I

love things that seem to work the first

time and every time in terms of our

natural biology based on a couple of

criteria there's an established

mechanism um it's been explored in the

context of pathology like mental health

disorders as well as pro- health in

healthy individuals um that it make

really good sense at the level of kind

of um uh Wellness uh uh and let's just

say ancient Health you know when you're

talking about getting a lot of sunlight

during the day like a lot of people say

well of course get outside and play not

getting too much light at night of

course this is just good old quote

unquote good oldfashioned advice people

spend 90% of their time indoors now

their daytime environments are too dim

their nighttime environments are too

bright and this kind of misleading

aspect of artificial light that when you

see a bright bulb you think I'm getting

a a lot of photons is part of the

problem and the fact that when you're

out on a overcast day and it you know

you think there Sun quote unquote isn't

out well it's hidden by cloud cover but

just think about how well you can

navigate that environment without a

flashlight yeah versus at night where

you would require a flashlight we

evolved under this tramatic difference

in day night availability of photons

independent of whether or not you can

quote see the sun and it's just very

clear that our the all the mechanisms in

our brain and body that regulate mood

are just powerfully regulated by this

stuff so I've made it a point to really

reduce the amount of nighttime light

that I'm getting but I am less concerned

about flipping on the light switch to

use the bathroom as I used to be I used

to think oh I'm like quashing all my

melatonin this is terrible I know I

can't shift my circadian clock then I

know that that light yes while it's

bright if it's brief I'm not going to

worry about it too much would it be

better to have a you you know a dim

light on as opposed to a bright light

sure but I'm not going to stress it in a

hotel bathroom or something I'm not

going to walk around you know shielding

my eyes people sometimes ask me by the

way is it different to look at the phone

directly versus if you tilt the phone

away well it absolutely is I mean think

about a flashl shown on the ground in

front of you very few photons getting in

your eyes versus shown directly into

your eyes think about the ambient light

from the Sun going everywhere versus

looking in the general direction of the

Sun so East in the morning West in the

afternoon of course

the directionality of the light matters

so I'm not saying it you know that you

need to like peek at your phone as if

you're looking you know over the edge of

a bowl or something into it but my

friend Samar hataru is head of the

chronobiology unit at the National

Institutes of mental health we used to

room together at meetings we stopped

because he's a terrible snorer so I just

could I there were a few times when I

considered suffocating him in the middle

of the night since he was already

suffocating himself now we just we don't

stay in the same rooms anymore we're no

longer postt talk

but I caught him looking at his phone in

the middle of the night and he would

tilt it like away like he's holding a

platter for those are just listening and

and kind of like looking over at the

screen there I'm like what are you doing

this is ridiculous he said I'm trying

not to get so much light in my eyes

that's a little extreme but I think it

illustrates the point which is how much

direct light exposure you get at night

matters how much direct sunlight

exposure you get especially early in

late early morning late afternoon and

throughout the day it really matters now

remind me Andrew what is the wavelength

of sunlight great so sunlight is going

to include all visible visible which

runs from how many yeah so well let's

let's we can answer two questions there

this wrist sensor detected 470 degree 70

nanometer to 650 nanometer light so

that's going to be blue and UltraViolet

ultraviolet is kind of kind of like blue

to Orange yeah blue blue to Orange

that's what this was measuring so red

light is going to be more like 680 um

far red is getting out to 7 720 and up

upwards of that blue light is going to

fall somewhere in the you know low fours

ultraviolet is getting down into the

high 3es and and lower um and so these

these Spectra of light so during the day

you know midday light you're get what

looks like white light you'll see oh the

sky is blue in the Sun is bright white

light it's not even yellow to your eye

and of course don't stare at it

especially in the middle of the

day you're getting all visible Spectra

so you're getting everything from UV all

the way out to Red Light it's just

coming in at equ intensities so is that

a potential limitation of this study in

that it didn't have a sensor that could

pick up the full spectrum of light

potentially especially since they're you

know we don't think of humans as UV uh

capable like we can't perceive UV light

um like a a ground squirrel for instance

can has UV sensors in its eyes turns out

you know why they use this it's crazy

they actually you know when the ground

squirrels sit up on their hunches

they're actually signaling one another

they rub urine on their belly and it

reflects UV um the the New York Times

for some reason has been running a

series of papers uh or articles rather

about uh naturally occurring fluoresence

at night in all sorts of scorpions and

uh monotes like the Platypus no one

really knows the reason for these odd

odd wavelength of light emissions for

for all these animals but you know we

view things in the blue violet and up to

red and you know we're not pit vipers we

can't see far red but we can see lower

than 470 nimet and we can see higher

than uh 7 650 is there a technology

reason why they had such a narrow band

in these sensors is it not possible that

they could have used a wrist sensor that

was wider this study was initiated in

2013 the tech was probably far worse

than it is now again I would love for

somebody to design an eyeglass where

it's measuring how many photons you're

getting across the day I'm not a big fan

of having everything be app IED so I

would love it if the frame would just

shift color across the morning like you

go outside on a cloudy day you know you

wear these glasses and um and by the way

it's fine to where eyeglasses or

contacts for sunlight viewing for

setting your circadian rhythm um people

always say well why is it that okay and

a window is not well corrective lenses

are actually focusing the light onto

your retina the windows and and

windshields are scattering the light and

filtering and how much are sunglasses

filtering this out way too much we can

safely say way too much probably causing

it

tfold decrement in the total Lux count

that's landing on your retina but of

course I you know sunglasses are

important driving into into sun and um

and some people have very sensitive eyes

I can't sit at a cafe with a bright

brightly reflective table in the

afternoon I just I just squint like

crazy I can't do it my dad who's you

know darker eyed you know he's South

South American descent he um you know he

can just sit there just fine my mom

who's got light eyes like me and you

know we're like oh it's really tough

just have a terrible time um you know

people differ in their light

sensitivity so there's one other macro

question I have here and it's not

answerable because without randomization

we can't know it but it's the question

of how much reverse causality can exist

in these observations so again these

observations um demonstrate very tight

correlations very strong associations

especially in the five areas that we

highlighted um

but it's possible that part of what

we're

seeing um is reverse causality brought

on by both the treatments which you've

already kind of alluded to and also the

condition itself do you want to explain

reverse causality for people and maybe

could you mention um for those that

missed uh the Hawthorne effect just yeah

yeah the the Hawthorne effect uh is is

is an effect that is named after you

know an observation of what took place

in a factory where they were actually

studying worker productivity with light

of all things um but what refers to is

the idea that people will change their

behavior when they are observed so if um

if I said well I really want to know

what a day in the life is like for

Andrew huberman I'm going to follow him

around for a day it's very unlikely that

his behavior that day will be exactly as

it was if I wasn't there re why you

probably will never see a day in the

life of Andrew huberman although it's

pretty it's pretty scripted unless I'm

traveling it's a it's a you know it's

morning sunlight hydration and you know

some cardio or weight training and then

a lot of time reading papers it'd be the

most boring video in the world because

mostly me reading and underlining things

but it's why um gamifying things can be

beneficial right it's why a CGM can can

be beneficial because it's sort of like

somebody's watching you and you're going

to modify what you eat in response to it

or why tracking can really be an

effective way to reduce input because

you there's a sense of being monitored

by doing that especially if someone

literally monitors it in other words you

can set up an accountability partner

where your health coach or someone is

actually seeing the data so that's what

it is now as far as reverse causality

when you look at variables so

um let's just pick u a common one that's

unrelated to this so there there's an

association that more diet soda

consumption is associated with greater

obesity it's a bit paradoxical right um

is that true it is yeah it's it's been

demonstrated in many series that the the

the greater the consumption of diet soda

the greater the prevalence of obesity

and that has been postulated by some to

suggest that non-nutritive sweeteners

such as aspartame or sucrose or things

like that are actually part of what's

causing

obesity um and while while there are

probably some arguments you could make

around the impact that those things

might have on the gut microbiome and

maybe there's some way and that's

happening it's also equally likely if

not probably more likely that there's

reverse causality there that a person

who is obese is therefore contemplating

how much they're eating or thinking hey

what's an easy way that I can reduce

calories how about instead of drinking a

Coke I drink a Diet Coke and so there

the causality which you would impute to

mean the drink is causing the Obesity it

might be no the Obesity is causing the

choice of drink so here the question is

um how much of the effect we're seeing

is a result of the condition that's

being studied right how much of the

disruption in both day and night ex uh

light exposure is the result of the

depression it's disregulated the sleep

maybe they sleeping more during the day

and more awake at night because of

depression again these are you can't

know this this is where epidemiology

never allows us to determine this and

sadly these questions can only be

answered through either direct

randomization or mandelian randomization

which by the way I was going to also ask

you do you know if anyone has examined

this from a mandelian standpoint that

would be that would be very interesting

because I have to

believe well it would be interesting I

don't know enough about the biology to

know what Snips would be studi but that

would be interesting what Peter is

saying is you know if you knew something

about the genomes of these

people um you would be in a great

position to perhaps even link up light

susceptibility genes or light light

sensitivity genes with genes for you

know Pathways involved in major

depression bipolar I mean get getting to

this issue of reverse causality I mean I

think it's very straightforward to

imagine that the person who's

experiencing a manic episode is going to

be up for two weeks at a time um sadly

and getting a lot of nighttime light

exposure you know now dark nighttime

dark exposure as a treatment for bipolar

is something that people are starting to

talk about so making sure that even

those people are awake that they're at

least blue blocking at night um reducing

their online activities but people with

severe manic episodes have a hard time

regulating their own behavior of course

and it's not one or the other like I

don't want the question to come across

to the listener that it has to be one or

the other it's only a can cause b or B

can cause a no it's actually a lot of

times these things feed off each other

going back to the soda example I

actually think there's a bit of both

right I I actually think there's a real

clear um body habitus dictates beverage

choice but I also am starting to think

that um ins susceptible individuals

non-nutritive sweeteners will alter the

gut biome and that alters metabolism

what about just hunger I I remember Lane

telling me and I I've seen at least at

least one of the studies that you know

water is probably better for us than

diet soda but that for some people diet

soda is a great tool for reducing

caloric intake I also know some

individuals not me who drink diet soda I

I drink diet soda from time to time

mainly Stevia sweeten sodas but but what

I'm referring to here are people besides

myself who drink diet soda and it seems

to stimulate their appetite there's

something about the the the perception

of sweet as driving hunger whereas not

eating uh or drinking anything with

calor with any sweetness doesn't seem to

this is one of the things I I wonder um

if it impacts why some people like

intermittent fasting because for some

people you know just even the the

perception I wonder if the perception of

sweetness or this even just the smell of

food we know can stimulate appetite so

you can imagine the perception of

Sweetness in the mouth even if there's

no calories there um I don't think it

necessarily makes people hypo glycemic

but perhaps it makes them think about M

like sweet means food for instance for

years I love the combination of a Diet

Coke and a slice of pizza whenever I was

in New York ideally two slices of pizza

so now every time I have a Diet Coke

which isn't that often but I like Diet

Coke especially with a little bit of

lemon in it I just think about a slice

of cheese or mushroom or pepperoni pizza

it's like I want it I crave it more so

there's a parot Association there that I

think is real and we know based on Dana

Small's Lab at Yale that there's this

paired association between the uh

sweetness from sucralose and there's an

insulin response they actually had to

Cease the study in kids because they

were they were becoming pre-diabetic you

know which unfortunately meant the study

was never published have you talked to

Dana on this podcast no we we wrote a

premium newsletter on this um several

months ago it it's got to be like I

don't know 10 to 20,000 words on all

things related to sugar substitutes I'll

read that so yeah folks who are

interested in this topic um I would

refer them to the premium newsletter on

sugar substitutes I think it was our

September Edition um the short of it is

the data are a little bit noisy um but

but there is indeed some some sweeteners

in some studies do do result in that

phenomenon you described the calic

insulin response

um and I came away from the research

that went into that which was Herculean

effort um on the part of the team

uh a little bit more confused than when

I went in

but um being even more cautious around

artificial sweeteners than I was going

in and not for the

reasons that I don't necessarily I don't

I didn't find any evidence that these

things are cancer-causing right so

that's the headline stuff people worry

about oh as like like 10 gr crazy I came

away more confident that from a from a

long-term safety perspective in terms of

met in terms of you know cancer and

catastrophic outcomes like that that

wasn't the issue but I came away much

more cautious around these things can

really be mucking around with both your

brain chemistry and your gut chemistry

which can pertain to your metabolism and

therefore my takeaway was buy or beware

use limited amounts only the one by the

way that still emerged to me is a

reasonable one it's the only one that I

use and I've talked about it a lot is

Xylitol xylitol is the pardon me I

shouldn't say that Xylitol for chewing

so for gum um and allulose as an

additive so those were the safer you're

saying yes those are those are basically

the only two I will consume yeah I'll

I'll drink a Diet Coke every now and

again if I'm on a plane or something you

know this law that got passed a few

years ago you couldn't bring liquids in

of your own into the airport and onto

the plane like what a great few years

ago what a great scheme what a great

scheme to get people to buy over

overpriced fluids in the airport like I

mean there are more important issues in

the world but like this one really gets

me um but yeah I I use a little bit I

drink things with a little bit of stevia

in it the occasional um Diet Coke um and

I I generally avoid sucrose I don't like

the way it tastes monk fruit is too

sweet but yeah we could we maybe we'll

do a a podcast on that in the future

okay so I think we can wrap this paper

because I really well but tell me what

you think about that point Andrew like

how I mean you know you you know more

about this stuff than I do but if if you

had to just lay on your judgment right

so so if it were if it were 100 to zero

you would say the light is 100% causal

in the effects we're seeing if it were

zero to 100 you'd say nope the behavior

is 100% causal of the exposure to light

where do you again you can't know it but

what does your intuition tell you okay

there's my intuition and then there's my

recognition of my own bias um because

you know I started working on these

circadian Pathways origin in the eye

back in year in 98 as a graduate student

at Berkeley the the cells these melanops

and intrinsically sensive retinal

gangling cells were discovered in the

early 2000s by a guy named Iggy

provencio Dave Bon Sam hatar sain panta

and others but and it was like one of

the most important discoveries in all of

biology clearly um so I've been very

excited about systems but if I set that

aside so um bias disclosure

made I think 65 to

75% of the effects are likely due to

light directly now it's impossible to

tease those apart as you mentioned but

to play Devil's Advocate against myself

you know you could imagine that the

depressed individual is laying around

indoors with the curtains drawn they

didn't sleep well the night before which

gives you a photo sensitivity that isn't

Pleasant like it sucks to have bright

light in your eyes first thing in the

morning if you especially if especially

if you didn't sleep well and then

they're you know making their coffee in

a dimly lit what they think is brightly

lit environment and then they're you

know looking at their phone and the the

state of the world sucks and their state

of their internal landscape is rough and

they're maybe they're dealing with a

pain or or you know injury or something

and their likelihood of getting outside

is is low and when they do get outside

they're going to shuffle and not you

know so I could see how the behaviors

could really limit the amount of of

light exposure and then evening rolls

around they've been tired all day and a

common symptom of depression you fall

asleep and then 2 or three in the

morning they're wide awake what are you

going to do at two or three when you're

Wide Awake sit in the dark no you're

going to get online you're going to

listen to things you might have I'm not

recommending this but a alcoholic drink

in order to try and fall asleep I mean

this is the pattern and so you know

shaking up that pattern is really what

what what so much of my public

health work these days is about and

trying to get people onto a more natural

daylight night uh night dark Rhythm uh

but yeah it's impossible to tease apart

we do know this and this is uh really

serious we know that in almost every

instance EV almost every Psychopathology

report of

suicide in the weeks but especially in

the days preceding suicide that person's

circadian rhythms looked almost inverted

from the normal

patterns and that's true of nonbipolar

individuals as well you know circadian

disruption and disruption in psychiatric

Health are

inextricable conversely positive mood

and affect and and circadian Behavior

seem very correlated I mean I think um

it's clear that if you want to become an

early riser get light in your eyes and

get activity in your body early in the

day you you built that you entrained to

those rhythms so that you start to

anticipate that morning workout you

start to anticipate the morning sunlight

just one um more scientific point we

know that when you view bright bright

sunlight in the morning or just sunlight

that's illuminating your environment as

you said you don't even have to see the

sun itself that there's a 55 z% increase

in the amplitude of the morning cortisol

Spike which is a good thing right that's

when you want it because it's inversely

the amplitude of the morning cortisol

spike is inversely related to the

amplitude of the evening cortisol Spike

and high evening cour is law is

associated with middle of the night

waking and on and on so um you know I'm

very bullish on these mechanisms I also

love that they're so deeply woven into

our evolutionary history you know that

we share with single cell organisms it's

so wild um but of course there's going

to be a bidirectionality there and it's

it's impossible to see where one thing

starts and the other one stops I mean

here's my take Andrew first of all I I

actually with far less Authority than

you um agree with your assessment and

might even be a little bit more bullish

might even put it at 8020 and and here

I'll I'll give you my explanations which

uh stem more from my fastidious battles

with epidemiology in general right like

because so much of the world that I live

in still has to rely on epidemiologic

data and so how do you make sense of it

and the truth of it is most of it is

really pretty bad um but I I tend to

find myself looking at the Austin

Bradford Hill criteria all the time and

for folks who don't know um he was a

statistician who basically proposed a

set of criteria U believe there are

eight of them and I can't believe I

don't know every one of them off by

heart I certainly used to um but the

more of these criteria that are met

within your correlations the more

likelihood uh you will find causality so

when I think of your data here the data

in this paper I'll tell you what makes

these correlations seem to have

causality within them in the direction

that's being

proposed um look at the dose effect so

dose effect matters and this is done in

quartiles and that's a very elegant

thing if they just did it as on off it

would be harder high low that's right

but the fact that they done in quartiles

allows you to see that every example in

figure two I don't believe there is an

exception to this no and I think also in

the in the other there's only one

exception to what I'm about to say sorry

two out of like God knows how many

they're all monotonically increasing and

decreasing in other words the dose

effect is always present another thing

is biologic plausibility you've spoken

at length about that today so in other

words sometimes you have to look at

epidemiology and ask is there a biologic

explanation and here there is you've

added another one which is evolutionary

conservation to the biologic

plausibility then you can talk about

animal models or experiments in humans

over short durations

that generally support these findings

and and so those are just a couple of

the the Bradford Hill criteria that that

lead to um you know my belief that yeah

there's reverse causality here but um

it's not the full explanation and that

more of the explanation is probably the

direction that's being proposed um and

if that's true because then at the end

of the day like what's the purpose of

the discussion the purpose of the

discussion is if you are under the

influence of any of these psychiatric

conditions in addition to the treatments

you're doing now what else can you do

and to me the takeaway is follow these

light behaviors I mean it's it's it's a

that's a relatively low lift when you

consider some of the other things like

I'm over here asking people to do Zone 2

for three hours a week and VO2 max

workouts and all this other stuff and

like I think all those things matter for

mental health as much as physical health

but this strikes me as on the spectrum

of low

asks if it shows if it's only even 30%

causality 70% reverse causality like

I'll take those I I would still instate

that yeah and it's you know it's taking

your coffee on the balcony it's and

people will often say well how do you do

this with kids the kids should be doing

it too right you know it means popping

your sunglasses off it means getting out

for just a few minutes and the fact that

it's additive that these you know these

Photon uh mechanis Photon counting

mechanisms they some is great and look

this paper also says and I should have

stated this earlier if you missed your

daytime light ration get your nighttime

dark ration they are independent and

additive so that's I mean that's a