Using Light (Sunlight, Blue Light & Red Light) to Optimize Health | Huberman Lab Podcast #68

- Welcome to the Huberman Lab Podcast,

where we discuss science and science-based tools

for everyday life.

[upbeat music]

I'm Andrew Huberman,

and I'm a professor of neurobiology and ophthalmology

at Stanford School of Medicine.

Today, we are going to discuss light

and the many powerful uses of light to optimize our health.

We're going to discuss the use of light

for optimizing skin health, appearance, and longevity,

for wound healing, for optimizing hormone balance,

and for regulating sleep, alertness, mood,

and even for offsetting dementia.

One of the reasons why light has such powerful effects

on so many different aspects of our biology

is that it can be translated into electrical signals

in our brain and body,

into hormone signals in our brain and body,

and indeed into what we call

cascades of biological pathways,

meaning light can actually change the genes

that the cells of your bodies express.

And that is true throughout the lifespan.

Today, I will discuss the mechanisms

by which all of that occurs.

I promise to make it clear for those of you

that don't have a biology background.

And if you do have a biology background,

I'll try and provide sufficient depth

so that it's still of interest to you.

And I promise to give you tools,

very specific protocols that are extracted

from the peer-reviewed literature

that will allow you to use different so-called wave lengths,

which most of us think of as colors,

of light in order to modulate your health

in the ways that are most important to you.

For those of you that are thinking

that the use of light to modulate health

falls under the category of woo science,

pseudoscience, or biohacking,

well, nothing could be further from the truth.

In fact, in 1903, the Nobel Prize was given to Niels Finsen,

he was Icelandic, he lived in Denmark,

for the use of phototherapy for the treatment of lupus.

So there's more than a hundred years of quality science

emphasizing the use of light,

and as you'll soon see, the use of particular wavelengths

or colors of light in order to modulate the activity

of cells in the brain and body.

So while it is the case that many places and companies

are selling therapies and products

related to the use of flashing lights and colored lights,

promising specific outcomes from everything

from stem cell renewal to improvement of brain function,

and some of those don't have any basis in science,

there are photo therapies that do have a strong foundation

in quality science,

and those are the studies and the protocols

that we are going to discuss today.

But I thought that people might appreciate knowing that

over a hundred years ago,

people were thinking about the use of light

for the treatment of various diseases

and for improving health.

And indeed many of those therapies are used today

in high quality hospitals and research institutions

and, of course, clinics and homes around the world.

One of the more exciting examples of phototherapy

in the last few years

is the beautiful work of Dr. Glen Jeffery

at University College London.

The Jeffery Lab is known for doing pioneering

and very rigorous research

in the realm of visual neuroscience.

And in the last decade or so,

they turned their attention to exploring the role

of red light therapy for offsetting age-related vision loss.

What they discovered is that just brief exposures

to red light early in the day

can offset much of the vision loss

that occurs in people 40 years or older.

And what's remarkable about these studies

is that the entire duration of the therapy

is just one to three minutes,

done just a few times per week.

What's even more exciting

is that they understand the mechanism

by which this occurred.

The cells in the back of the eye

that convert light information into electrical signals

that the rest of the brain can understand

and create visual images from,

well, those cells are extremely metabolically active.

They need a lot of ATP or energy.

And as we age,

those cells get less efficient

at creating that ATP and energy.

Exposure to red light early in the day,

and it does have to be early in the day,

allowed those cells to replenish the mechanisms

by which they create ATP.

I'll talk about these experiments

in more detail later in the episode

and the protocols so that you could apply those protocols

should you choose.

But I use this as an example of our growing understanding

of not just that phototherapies work but how they work.

And it is through the linking of protocols and mechanism

that we, meaning all of us,

can start to apply phototherapies

in a rational, safe, and powerful way.

I'm pleased to announce

that I'm hosting two live events this May.

The first live event will be hosted

in Seattle, Washington on May 17th.

The second live event will be hosted

in Portland, Oregon on May 18th.

Both are part of a lecture series entitled

The Brain Body Contract,

during which I will discuss science and science-based tools

for mental health, physical health, and performance.

And I should point out

that while some of the material I'll cover

will overlap with information covered here

on the Huberman Lab Podcast

and on various social media posts,

most of the information I will cover is going to be distinct

from information covered on the podcast or elsewhere.

So once again, it's Seattle on May 17th,

Portland on May 18th.

You can access tickets by going to hubermanlab.com/tour.

And I hope to see you there.

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 public.

In keeping with that theme,

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Okay, let's talk about light.

First, I want to talk about the physics of light,

and I promise to make that very clear,

even if you don't have a background in physics.

And then I want to talk about the biology of light,

meaning how light is converted into signals

that your brain and body can use

to impact things like organ health or disease,

or how it can use light

in order to repair particular organs,

like your skin, your eyes, your brain, et cetera.

The physics of light can be made very simple

by just illustrating a few key bullet points.

The first bullet point

is that light is electromagnetic energy.

If the word electromagnetic feels daunting to you,

well, then just discard that

and just think of light as energy

and think of energy as something

that can impact other things in its environment.

Now, the way to imagine light

or to conceptualize light as energy

is that all around you light is traveling

in these little wavelengths.

And the reason, for those of you that are watching,

I'm making a little wavey motion with my hand

is that's actually the way

that light energy moves in little waves.

Just like sound waves are coming at you

and impinging on your ears,

if you can hear me talking right now,

that is happening,

those are sound waves,

meaning the movement of air particles out there

impacting your ear drum.

Well, light energy is just little bits

of electromagnetic energy traveling through your environment

all the time in these little waves

and impinging on your brain and body and eyes, et cetera.

And as I mentioned before,

energy can change the way that other things behave.

It can cause reactions in cells of your body.

It can cause reactions in fruit, for instance, right?

You see a piece of fruit and it's not ripe,

but it gets a lot of sunlight and it ripens.

That's because the electromagnetic energy of sunlight

had an impact on that plant or that tree,

or even on the fruit directly.

As a parallel example of energy

and its ability to impact other things,

we are all familiar with food

and the fact that food has calories.

Calorie is a measure of energy.

It has everything to do with how much heat is generated

when you burn a particular article of food,

believe it or not.

And it turns out that how hot a given article of food burns

gives you a sense of how much energy

it can provide your body

in terms of your body's ability to store or use that energy.

So again, think of light as electromagnetic energy,

but really put that word energy into capital letters,

embed that in your mind, going forward,

and you'll understand most of the first bullet point

of what light is in terms of the physics of light.

Now, the second thing that you need to understand

about the physics of light

is that light has many different wavelengths,

and the simplest way to conceptualize this

is to imagine that cover of that Pink Floyd album,

where there's a prism.

You have a white beam of light going into that prism.

And then the prism splits that beam of light

into what looks like a rainbow.

So you got your reds, your orange, your greens,

your blues, your purples, et cetera.

Anytime we have light in our environment,

that is so-called white light.

It includes all those wavelengths,

but sunlight and other forms of light

also have other wavelengths of light that we can't see.

So when we think about the rainbow,

that's just the visible spectrum of light.

There are also wavelengths of light

that are not visible to us,

but that are visible to some other animals,

and that can still impact your brain and body

because there is still energy at those wavelengths.

I'll give a few examples of this.

Humans are not a species that can see

into the infrared realm of the spectrum.

A pit viper, meaning a snake that has infrared sensors,

however, can sense in the infrared.

So if you were to walk through a jungle

and there's a pit viper there,

it sees you as a cloud of heat emission

because your body is emitting infrared energy all the time.

You're casting off infrared energy.

The snake can see it, you can't.

If you were to put on a particular set of goggles

that were infrared goggles,

well, then you would be able to see the heat emissions

of any organism, human or otherwise,

that could emit infrared energy.

Let's take the opposite end of the spectrum.

We are familiar with seeing things

that are blue or green or very pale blue.

But as we say below that,

meaning even shorter wavelength light is out there.

Ultraviolet light is a really good example of light energy

that's coming from the sun and is in our environment

and is being reflected off surfaces all the time.

We don't see it.

And yet, if it's very bright outside,

that ultraviolet light can burn our skin.

As you'll learn in today's episode,

ultraviolet light can also positively impact us.

In fact, I will describe a particular set

of new results that show that ultraviolet light

viewed for just a few minutes each day,

or landing on the skin for just a few minutes each day,

can actually offset a lot of pain.

It actually has the ability to reduce the amount

of pain sensed by your body.

And we now understand the specific circuits in the brain

and body that allow that to happen.

I'll talk about that

and the related protocols a little bit later.

So the important thing to understand

about the physics of light

is that there's energy at all these different wavelengths.

We only see some of those wavelengths,

which basically is to say that light impacts us

at many different levels.

And the so-called levels that I'm referring to

are the different wavelengths of light.

And you're welcome to think

of the different wavelengths of light as different colors,

but do understand that there are truly colors of light

that you and I can't see,

and yet that have powerful impact on your brain and body.

Now, the third bullet point to understand

about the physics of light

is that different wavelengths of light,

because of the way that their wave travels,

can penetrate tissues to different depths.

This is very, very important.

Today, we're going to talk a lot about red light therapies

and near-infrared light therapies.

Those are so called longer wavelengths.

Longer wavelengths, just think

of a bigger, longer wave, right?

A bigger curve, as opposed to short wavelength light,

which is going to be shorter, right?

A short wavelength light would be something

like blue or green light or ultraviolet light.

Blue, green, and ultraviolet light,

because its shortwave length light,

doesn't tend to penetrate tissues very easily.

It has to do with the way that the physics of light

interacts with the physical properties of your skin

and other tissues of your body.

But basically, if you were to shine UV light

onto your arm, for instance,

it could impact the skin on the surface of the arm,

maybe some of the cells just beneath the top layer of skin,

but it wouldn't penetrate much deeper.

Long wavelength light like red light and near-infrared light

has this amazing ability to penetrate through tissues,

including your skin.

And so if we were to shine red light

or near-infrared light onto your arm,

it would pass through that top layer of skin.

It might impact it a little bit,

but it could penetrate deeper into your skin,

not just to the skin layers,

but maybe even down to the bone,

maybe even down to the bone marrow.

And for many people, this will be hard to conceptualize.

You think, "Well, wait, I've got the skin there.

Doesn't the light just bounce off?"

And the answer is no,

because of the way that long wavelength light

interacts with the absorbance properties of your skin.

Absorbance properties are just the way

that the skin takes light energy

and converts it into a different form of energy.

And your skin is not able to take long wavelength light,

like red light and near-infrared light, and absorb it.

But the tissues deeper in your body can.

So if you shine a red light or near-infrared light

onto the surface of your skin,

you'll see a red glow there

as a reflectance on the surface of your skin.

But a lot of the photon energy,

the light energy in those longer wavelengths

is indeed passing through those top layers of skin,

into the deeper layers of skin,

and can even make it into the deep layers of your arm.

And as we start to transition from the physics of light

to the biological impacts of light,

just understanding that the different wavelengths of light

impact our tissues at different levels,

literally at different depths,

will help you better understand

how light of different colors, of different intensities

and how long you are exposed to those colors

and intensities of light can change the way that the cells

and the organs of your body work.

And if it didn't sound weird enough

that you can pass light through particular tissues

and have them land and be absorbed

at tissues deeper in your body,

well, it turns out that different wavelengths of light

are also best absorbed by particular so-called organelles

within your cells.

What are organelles?

Organelles are the different compartments

and different functions within a given cell.

So for instance, your mitochondria,

which are responsible for generating ATP

and energy in your cells,

those exist at a particular depth,

at a particular location within a cell.

They're not all at the cell surface.

They sit somewhat deeper in the cell.

The nucleus of your individual cells contains DNA,

and that sits at a particular depth or location

within your cell.

Different wavelengths of light

not only can penetrate down into different tissues

and into different cells of your body,

but they can also penetrate

and access particular organelles,

meaning mitochondria or the nucleus

or the different aspects of your cells

that are responsible for different functions.

This is exquisitely important, and it's exquisitely powerful

because as you'll learn today,

particular wavelengths of light can be used

to stimulate the function of particular organelles

within particular cells,

within particular organs of your body.

I can think of no other form of energy, not sound,

not chemical energy, so not drugs,

not food, not touch, no form of energy

that can target the particular locations

in our cells, in our organelles,

in our organs and in our body,

to the extent that light can.

In other words, if you had to imagine

a real world surgical tool by which to modulate our biology,

light would be the sharpest

and the most precise of those tools.

Now, let's talk about how light is converted

into biological signals.

There's several ways in which that is accomplished,

but the fundamental thing to understand

is this notion of absorption of light energy.

Certain pigments or colors

in the thing that is receiving the light energy,

meaning the thing that the light energy lands on,

are going to absorb particular wavelengths of light.

Now, I promise you that you already intuitively know

how this works.

For instance, if you were to sit outside

on a very bright sunny day,

and you had a table in front of you that was metal,

you might find it hard to look down at that metal table

because it's reflecting a lot of light

of particular wavelengths.

If that table were pitch black, however,

it wouldn't reflect quite as much,

and you would be able to comfortably look at at it.

If that table were red, it might be somewhere in between.

If that table were green,

it would be also somewhere in between,

but let's say it were very light blue.

Well, then it might reflect almost as much as a table

that were just metal or a white table surface.

So the absorbance properties of a given surface

will determine whether or not light energy goes and stays

at that location and has an impact on that location

or whether or not it bounces off.

Every biological function of light

has to do with the absorbance or the reflectance of light

or light passing through that particular thing,

meaning that particular cell or compartment within a cell.

I'd like to make it clear how this works

by using the three primary examples

of how you take light in your environment

and convert it into biological events.

We have photoreceptors in the back of our eyes.

These photoreceptors come in two major types,

the so-called rods and the cones.

The rods are very elongated, they look like rods.

And the cones look like little triangles.

Rods and cones have within them photopigment.

They have dark stuff that's stacked up in little layers.

Rods absorb light of essentially any wavelength.

There's some variation to that,

but let's just say rods don't care

about the different colors of light.

They will absorb light energy, photon energy,

if it's red, if it's green, if it's blue,

if it's yellow, doesn't matter,

as long as that light is bright enough.

And it turns out that rods are very, very sensitive.

They can detect very, very small numbers of photons.

And rods are essentially what you use

to see in very low light conditions.

We'll return more to vision later.

The cones come in three major varieties.

At least for most people who aren't colorblind,

you have so-called red cones, green cones, and blue cones.

But they're not really red, green, and blue

in the back of your eye.

They are cones that either absorb

long wavelength light, red,

that absorb medium wavelength light, green,

or short wavelength light, blue.

The reason that they can absorb

different wavelengths of light

is they have different photopigments.

So much as the example I gave before,

where you have different tables outside

in the sunny environment,

and some are reflecting light more than others,

others are absorbing light more than others,

well, so too, the photoreceptors, meaning the cones,

are absorbing light of different wavelengths

to different extents.

And in an absolutely incredible way,

your brain is actually able to take that information

and create this perception that we have of color.

But that's another story altogether

that we'll just touch on a little bit more later,

but that if you want to learn all about,

you can go to our episode on vision.

So that's photoreceptors in the back of your eye,

absorbing light of different wavelengths, rods, and cones.

The other place, of course,

where light can impact our body

is on our surface, on our skin.

And skin has pigment too.

We call that pigment melanin.

We have within our skin multiple cell types,

but in the top layer of skin, which is called the epidermis,

we have keratinocytes, and we have melanocytes.

And the melanocytes are the cells

that create pigmentation of the skin.

And of course there is wide variation in the degree

to which there is pigmentation of the skin,

which has to do with genetics,

also has to do with where you were born and raised,

how much light exposure you have throughout the year, right?

So people toward the equator

tend to have more melanocyte activity

than people who are located at the North Pole.

And of course, people live at different locations

throughout the Earth,

regardless of their genetic background

or where they were born.

And so, as you all know, with light exposure,

those melanocytes will turn on genetic programs

and other biological programs

that lead to enhanced pigmentation of the skin,

which we call tanning.

The way they do that is by absorbing UV light specifically.

So with melanocytes,

we have a very specific example

of how a pigment absorbs light of a particular length,

in this case, ultraviolet shortwave length light,

which in turn creates a set of biological signals

within those cells that in turn creates changes

in our skin pigmentation.

So we have photoreceptors, we have melanocytes.

And the third example I'd like to provide

is that of every cell of your body.

And what I mean by that is that every cell of your body,

meaning a cell that is part of your bone tissue

or your bone marrow or heart tissue or liver or spleen,

if light can access those cells,

it will change the way that those cells function

for better or for worse.

For many organs within our body

that reside deep to our skin,

light never arrives at those cells.

A really good example of this

that we'll touch on later is the spleen.

Unless you have massive damage to your body surface,

unless you literally have a hole in your body,

light will never land directly on your spleen,

but the spleen still responds to light information

through indirect pathways.

And those indirect pathways arise

through light arriving on the skin

and light arriving on the eyes.

So a key principle

that I'm going to return to again and again today

is that the ways in which light can impact the biology

of your organelles, your cells,

your organs, and the tissues, and indeed your whole body,

can either be direct,

so for instance, light onto your skin impacting skin

or light onto your photoreceptors

impacting the photoreceptors of your eye,

or it can be indirect.

It can be light arriving on your photoreceptors,

the photoreceptors then informing another cell type,

which informs another cell type,

which then relays a signal

in kind of a bucket brigade manner

off to the spleen and says to the spleen,

"Hey, there's a lot of UV light out here.

We're actually under stress.

In fact, there's so much UV light

that you need to activate an immune program

to protect the skin."

And in response to that,

the spleen can deploy certain signals in certain cell types

to go out and start repairing skin

that's being damaged by UV light.

So we have direct signals and we have indirect signals,

but in every case,

it starts with light of particular wavelengths

being absorbed by particular pigments or properties

of the surfaces that those light waves land on.

And as you recall from our discussion

about the physics of light, remember,

it's not just about light impinging

on the surface of your body.

Light can actually penetrate deep to the skin

and access at least certain tissues and cells of your body.

Even though you can't see those wavelengths of light,

they are getting into you all the time.

So perhaps the best way to wrap this discussion

about the physics and the biology of light

with a bit of a bow

is to think about light as a transducer,

meaning a communicator of what's going on

in the environment around you

and that some of those signals are arriving at the surface

and impacting the surface of your body.

But many of those signals are being taken by cells

at the surface of your body,

meaning your melanocytes in your skin

and the photoreceptors of your eyes,

and then being passed off as a set of instructions

to the other organs and tissues of your body.

Light can impact our biology in very fast,

moderately fast, and slow ways.

But even the slow ways in which light can impact our biology

can be very powerful and very long-lasting.

Just as a quick example of the rapid effects

of light on our biology,

if you were to go from a room that is dimly lit or dark

into a very brightly lit room,

you would immediately feel very alert.

You might say, "No, that's the not true.

Sometimes I wake up and it's dark, and I kind of stumble out

and it's lighter out in the next room.

And it takes me a while to wake up."

Ah, but if we were to move you from a room

that was very dark to very bright,

a signal conveyed from your eyes

to an area of your brain stem called the locus coeruleus

would cause the release of adrenaline

similar to the release of adrenaline

if you were to be dropped into very, very cold water

all of a sudden.

Just an immediate wake-up signal to your brain and body.

So that's an example of a rapid effect

of light on your biology,

not a very typical one, but nonetheless,

one that has a hardwired biological mechanism.

At the other end of the spectrum

are what we call slow integrating effects of light

on our biology.

So what I mean by that are ways in which your body

is taking information about light in the environment,

not in the sort of snapshot, acute sense,

but averaging the amount of light in your environment.

And that average light information

is changing the way that your biology works.

But even though this is a slow process,

as I mentioned before, it's a very powerful one.

The primary example of this

are so-called circannual rhythms.

Circannual rhythms are literally a calendar

that exists within your body that uses not numbers,

but amounts of hormone that are released

into your brain and body each day and each night

as a way of knowing where you are

in the 365-day calendar year.

Now that might seem kind of crazy, but it's not crazy.

The Earth travels around the sun once every 365 days.

And depending on where you are on the Earth, where you live,

you are going to get more or less light each day on average,

depending on the time of year.

So if you're in the Northern Hemisphere,

in the winter months, days are shorter, nights are longer.

In the summer months, days are longer, nights are shorter.

And of course, things change whether or not you're

in the Northern Hemisphere or the Southern Hemisphere,

but nonetheless in short days you have more darkness,

that's obvious.

And if you understand that light arriving on the eyes

is absorbed by a particular cell type

called the intrinsically photosensitive ganglion cell.

It's just a name.

You don't need to know the name, but if you want,

it's the so-called intrinsically

photosensitive ganglion cell,

also called the melanopsin cell

because it contains an opsin,

a photopigment that absorbs shortwave length light

that arrives through sunlight.

Those cells communicate to particular stations in the brain

that in turn connect to your so-called pineal gland,

which is this little pea-sized gland

in the middle of your brain

that releases a hormone called melatonin.

And the only thing you need to know is that light

activates these particular cells,

the intrinsically photosensitive melanopsin cells,

which in turn shuts down the production of melatonin

from the pineal gland.

If you think about this in terms of the travel

of the Earth around the sun across the year,

what it means is that in short days,

because there's very little light on average

landing on these cells,

the duration of melatonin release will be much longer

because as I mentioned before, light inhibits,

it shuts down melatonin.

Whereas in the summer months, much more light on average

will land on your eyes, right?

Because days are longer.

Even if you're spending more time indoors,

on average, you're going to get more light

to activate these cells.

And because light shuts down melatonin production,

what you'll find is that the duration of melatonin release

for the pineal is much shorter.

So melatonin is a transducer.

It's a communicator of how much light on average

is in your physical environment.

What this means is

for people living in the Northern Hemisphere,

you're getting more melatonin release in the winter months

than you are in the summer months.

So you have a calendar system that is based in a hormone,

and that hormone is using light in order to determine

where you are in that journey around the sun.

Now, this is beautiful.

At least to me, it's beautiful

because what it means is that the environment around us

is converted into a signal

that changes the environment within us.

That signal is melatonin,

and melatonin is well known for its role

in making us sleepy each night

and allowing us to fall asleep.

Many of you have probably heard before,

I am not a big fan of melatonin supplementation

for a number of reasons, but just as a quick aside,

the levels of melatonin that are in most supplements

are far too high to really be considered physiological.

They are indeed super physiological in most cases,

and melatonin can have a number of different effects,

not just related to sleep,

but that's supplemented melatonin.

Here, I'm talking about our natural production

and release of melatonin

according to where we are in the 365-day calendar year.

Endogenous melatonin, meaning the melatonin

that we make within our bodies naturally,

not melatonin that's supplemented,

has two general categories of effects.

The first set of effects are so called regulatory effects

and the others are protective effects.

The regulatory effects are for instance,

that melatonin can positively impact bone mass.

So melatonin can, for instance,

turn on the production of osteoblasts,

which are essentially stem cells that make more bone for us

that make our bones stronger

and that can replace damaged aspects of our bone.

Melatonin is also involved in maturation

of the gonads during puberty, the ovaries and the testes.

Although there, the effects of melatonin

tend to be suppressive on maturation

of the ovaries and testes,

meaning high levels of melatonin

tend to reduce testicle volume

and reduce certain functions within the testes,

including sperm production and testosterone production.

And within the ovaries, melatonin can suppress

the maturation of eggs, et cetera.

Now, I don't want anyone to get scared

if you've been taking melatonin.

Most of the effects of melatonin

on those functions are reversible,

but I should point out that one of the reasons

why children don't go into puberty until a particular age

is that young children

tend to have chronically high endogenous melatonin.

And that is healthy to keep them out of puberty

until it's the right time for puberty to happen.

So melatonin can increase bone mass,

but reduces gonad mass, so to speak.

It's going to have varying effects

depending on the ratios and levels of other hormones

and other biological events in the body.

But as you can see,

melatonin has these powerful regulatory on other tissues.

I should also mention that melatonin is a powerful modulator

of placental development.

So for anyone that's pregnant,

if you're considering melatonin supplementation,

please, please, please talk to your OB/GYN,

talk to your other doctor as well.

You want to be very, very cautious

because of the powerful effects that melatonin can have

on the developing fetus and placenta.

For people that are not pregnant, in fact, all people,

melatonin has a powerful effect

on the central nervous system as a whole.

Your brain and spinal cord are the major components

of your central nervous system ,

and melatonin, because it's associated with darkness,

which is just another way of saying

that light suppresses melatonin,

melatonin is thereby associated with the dark phase

of each 24-hour cycle,

it can have a number of different effects

in terms of waking up or making our body feel more sleepy.

And it does that by way of impacting cells

within our nervous system,

literally turning on certain brain areas,

turning off other brain areas.

And it does that through a whole cascade

of biological mechanisms,

a bit too detailed to get into today.

So melatonin is regulating how awake or asleep we are.

It tends to make us more asleep, incidentally.

It's regulating our timing of puberty,

and it's regulating how our gonads,

the testes and ovaries, function,

even in adulthood, to some extent.

And it's regulating bone mass.

As I mentioned before,

melatonin also has protective effects.

It can activate our immune system.

It is among the most potent antioxidants.

So it is known to have certain anti-cancer properties

and things of that sort,

which is not to say that you simply want more melatonin.

I think a lot of people get misled

when they hear something like,

melatonin has anti-cancer properties.

That doesn't mean that cranking up the levels of melatonin

by supplementing it, or by spending time in darkness

and not getting any light,

which would, of course, inhibit melatonin,

is going to be beneficial for combating cancer.

That's not the way it works.

It is actually the rise and fall of melatonin

every 24-hour cycle

and the changes in the duration of that melatonin signal

throughout the seasons

that has these anti-cancer and antioxidant effects.

So when we think about light impacting our biology,

the reason I bring up melatonin

as the primary example of that

is A, because melatonin impacts so many important functions

within our brain and body,

but also because hormones in general, not always,

but in general, are responsible

for these slow modulatory effects on our biology.

And so I'm using this as an example

of how light throughout the year

is changing the way that the different cells

and tissues and organs of your body are working,

and that melatonin is the transducer of that signal.

So at this point,

we can say light powerfully modulates melatonin,

meaning it shuts down melatonin.

Melatonin is both beneficial for certain tissues

and suppressive for other tissues and functions.

What should we do with this information?

Well, it's very well established now

that one of the best things that we can all do

is to get the proper amount of sunlight each day.

And by proper, I mean appropriate for that time of year.

So in the summer months where the days are longer

and nights are shorter,

we would all do well to get more sunlight in our eyes.

And again, it's going to be to our eyes

because as you recall,

the pineal sits deep in the brain,

and light can't access the pineal directly,

at least not in humans.

So in order to get light information to the pineal

and thereby get the proper levels of melatonin

according to the time of year,

we should all try and get outside as much as possible

during the long days of summer and spring.

And in the winter months, it makes sense

to spend more time indoors.

For those of you that suffer

from seasonal effective disorder,

which is a seasonal depression,

or feel low during the fall and winter months,

there are ways to offset this.

We did an entire episode on mood and circadian rhythms

where we described this.

So it does make sense for some people

to get more bright light in their eyes early in the morning

and throughout the day during the winter months as well.

But nonetheless, changes in melatonin,

meaning changes in the duration

of melatonin release across the year are normal and healthy.

So provided that you're not suffering from depression,

it's going to be healthy to somewhat modulate your amount

of indoor and outdoor time across the year.

The other thing to understand

is this very firmly established fact,

which is light powerfully inhibits melatonin.

If you wake up in the middle of the night,

and you go into the bathroom and you flip on the lights,

and those are very bright, overhead, fluorescent lights,

your melatonin levels,

which would ordinarily be quite high

in the middle of the night

because you've been eyes closed in the dark, presumably,

will immediately plummet to near zero or zero.

We would all do well regardless of time of year

to not destroy our melatonin in the middle of the night

in this way.

So if you need to get up in the middle of the night

and use the restroom,

which is a perfectly normal behavior for many people,

use the minimum amount of light required

in order to safely move through the environment

that you need to move through.

Melatonin needs to come on early in the night.

It actually starts rising in the evening and towards sleep.

But then as you close your eyes and you go to sleep,

melatonin levels are going to continue to rise

at least for several hours into the night.

Again, if you get up in the middle of the night,

really try hard not to flip on a lot of bright lights.

If you do that every once in a while,

it's not going to be a problem.

But if you're doing that night after night,

you are really disrupting this fundamental signal

that occurs every night,

regardless of winter, spring, summer, et cetera.

And that is communicating information

about where your brain and body should be in time.

And I know that's a little bit of a tricky concept,

but really our body is not meant to function

in the same way during the winter months,

as the summer months.

There are functions that are specifically optimal

for the shorter days of winter.

And there are functions that are specifically optimal

for the longer or days of summer.

So again, try to avoid bright light exposure to your eyes

in the middle of the night.

And for those of you that are doing shift work,

what I can say is try and avoid getting bright light

in your eyes in the middle of your sleep cycle.

So even if you're sleeping in the middle of the day,

because you have to work at night,

if you wake up during that about of sleep,

really try hard to limit the amount of light,

which is going to be harder for shift workers, right?

Because there are generally a lot more lights on

and bright lights outside,

so you would want to close the blinds

and limit artificial light inside.

One way to bypass some of the inhibitory effects

of light on melatonin

is to change your physical environment

by, for instance, dimming the lights.

That's one simple way, very low-cost way.

In fact, you'll save money by dimming the lights

or turning them off.

The other is if you are going to use light,

using long wavelength light, because, as you recall,

these intrinsically photosensitive melanopsin cells

within your retina that convey the signal

about bright light in your environment

to impact melatonin, to shut down melatonin,

respond to short wavelengths of light.

So red light is long wavelength light.

You now understand that from our discussion

about the physics of light.

And if you were to use amber-colored light or red light

and even better, dim amber or dim red light

in the middle of the night,

well, then you would probably not reduce melatonin at all

unless those red lights and amber lights

are very, very bright.

Any light, provided it's bright enough,

will shut down melatonin production.

One final point about melatonin,

and this relates to melatonin supplementation as well,

is that now that you understand

how potently melatonin can impact things

like cardiovascular function, immune function,

anti-cancer properties, bone mass,

gonad function, et cetera,

you can understand why it would make sense

to be cautious about melatonin supplementation,

because supplementation tends to be pretty static.

It's X number of milligrams per night,

whereas normally endogenously the amount of melatonin

that you're releasing each night

is changing according to time of year,

or if you happen to live in an area

where there isn't much change in day length across the year,

so for instance, if you live near the equator,

well, then your body is accustomed to having regular amounts

of melatonin each night.

When you start supplementing melatonin,

you start changing the total amount of melatonin, obviously,

but you're also changing the normal rhythms

in how much melatonin is being released

into your brain and body

across the 365-day calendar year.

So while I'm somebody

who readily embraces supplementation in various forms,

for things like sleep and focus, et cetera,

when it comes to melatonin, I'm extremely cautious.

And I think it's also one of the few examples

where a hormone is available without prescription,

over the counter.

You just go into a pharmacy or drugstore or order online,

this hormone, which is known

to have all these powerful effects.

So I get very, very concerned

when I hear about people taking melatonin,

especially at the levels that are present

in most supplements.

It's been recognized for a very long time,

and in fact, there are now data to support the fact

that animals of all kinds, including humans,

will seek out mates and engage in mating behavior

more frequently during the long days of spring and summer.

That's right, in seasonally-breeding animals,

of course, this is the case,

but in humans as well,

there is more seeking out of mates and mating behavior

in longer day times of year.

Now, you could imagine at least two mechanisms

by which this occurs.

The first mechanism we could easily map to melatonin

and the fact that melatonin is suppressive

to various aspects of the so-called gonadal axis,

which is basically a fancy way of saying

that melatonin inhibits testosterone and estrogen output

from the testes and from the ovaries.

I just want to remind people that both males and females

make testosterone and estrogen,

although in different ratios, typically,

in males versus females,

and that both testosterone and estrogen

are critical for the desire to mate and for mating behavior.

There's a broad misconception that testosterone

is involved in mating behavior

and estrogen's involved in other behaviors,

but having enough estrogen is critical

for both males and females

in order to maintain the desire to mate,

and indeed the ability to mate.

I discuss this on the episode

on optimizing testosterone and estrogen.

So if you'd like more details on that,

please see that episode of the Huberman Lab Podcast.

Okay, so if melatonin is suppressive

to the so-called gonadal axis and reduces overall levels

of testosterone and estrogen in males and females

and a light inhibits melatonin,

then when there's more light, then there's less melatonin

and more hormone output from the gonads.

And indeed that's how the system works,

but that's not the entire story.

It turns out that there is a second

so-called parallel pathway,

meaning a different biological pathway

that operates in parallel

to the light suppression of melatonin pathway

that provides a basis for longer days,

inspiring more desire to mate and more mating behavior.

So if we think of the first pathway involving melatonin

as sort of a break on these reproductive hormones,

the second mechanism is more like an accelerator

on those hormones.

And yet it still involve light.

As I'm about to tell you, in animals such as mice,

but also in humans,

exposure to light, in particular UV blue light,

so short wavelengths of light,

can trigger increases in testosterone and estrogen

and the desire to mate.

Now what's especially important about this accelerator

on the desire to mate and mating behavior and hormones

is that it is driven by exposure to light,

but it is not the exposure of light to the eyes.

It turns out that it is the exposure of your skin

to particular wavelengths of light

that is triggering increases in the hormones,

testosterone, and estrogen,

leading to increased desire to mate.

As it turns out, your skin,

which most of us just think of as a way

to protect the organs of our body

or something to hang clothes on or ornaments on,

if you're somebody who has earrings and so forth,

your skin is actually an endocrine organ,

meaning it is a hormone-producing

and hormone-influencing organ.

I promise what I'm about to tell you next

will forever change the way that you think

about your skin and light and the desire to mate,

and indeed even mating behavior.

I think the results are best understood

by simply going through the primary data,

meaning the actual research on this topic.

And to do so, I'm going to review a recent paper

that was published in the Journal Cell Reports,

Cell Press Journal, excellent journal.

This is a paper that came out in 2021,

entitled "Skin Exposure to UVB light

induces a skin, brain, gonad axis, and sexual behavior.

And I want to emphasize that this was a paper

that focused on mice

in order to address specific mechanisms,

because in mice,

you can so-called knock out particular genes.

You can remove particular genes to understand mechanism.

You just can't do that in humans

in any kind of controlled way,

at least not at this point in time.

And this study also explores humans

and looked at human subjects, both men and women.

The basic finding of this study was that

when mice or humans were exposed to UVB,

meaning ultraviolet blue light, so shortwave length light

of the sort that comes through in sunshine,

but is also available through various artificial sources.

If they received enough exposure

of that light to their skin,

there were increases in testosterone that were observed

within a very brief period of time,

also increases in the hormone estrogen.

And I should point out that the proper ratios of estrogen

and testosterone were maintained in both males and females,

at least as far as these data indicate,

and mice tended to seek out mating more and mate more.

There were also increases in gonadal weight,

literally increases in testy size and in ovarian size

when mice were exposed to this UVB light

past a certain threshold.

Now, as I mentioned before, the study also looked at humans.

They did not look at testy size or ovarian size

in the human subjects.

However, because they're humans,

they did address the psychology of these human beings

and addressed whether or not they had increases

in, for instance, aggressiveness or in passionate feelings

and how their perception of other people changed

when they were getting a lot of UVB light exposure

to the skin.

So before I get into some of the more important details

of the study and how it was done

and how you can leverage this information for yourself,

if you desire,

I just want to highlight some of the basic findings overall.

UVB exposure increased these so-called sex steroid levels

in mice and humans.

The sex steroid hormones, when we say steroids,

we don't mean anabolic steroids taken exogenously.

I think when people hear the word steroids,

they always think steroid abuse or use, rather.

Steroid hormones, such as testosterone and estrogen,

went up when mice or humans had a lot of UVB exposure

to their skin.

Second of all, UVB light exposure to the skin

enhanced female attractiveness,

so the perceived attractiveness of females by males,

and increased the receptiveness

or the desire to mate in both sexes.

UVB light exposure also changed various aspects

of female biology related to fertility,

in particular follicle growth.

Follicle and egg maturation

are well-known indices of fertility,

and of course, correlate with the menstrual cycle

in adult humans and is related overall

to the propensity to become pregnant.

UVB light exposure enhanced maturation of the follicle,

which just meant that more healthy eggs were being produced.

These are impressive effects.

First of all, they looked at a large number

of variables in the study.

And the fact that they looked

at mice and humans is terrific.

I think that oftentimes we find it hard to translate data

from mice to humans.

So the fact that they looked at both in parallel

is wonderful.

In the mice and in the humans,

they established a protocol

that essentially involved exposing the skin to UV light

that was equivalent to about 20 to 30 minutes

of midday sun exposure.

Now, of course, where you live in the world

will dictate whether or not that midday sun

is very, very bright and intense or is less bright.

Maybe there's cloud cover, et cetera.

But since I'm imagining that most people are interested

in the ways to increase testosterone

and/or estrogen in humans

and are not so much interested

in increasing testosterone in mice,

I'm going to just review what they did

in the human population or the human subjects.

What they did is they had people,

first of all, establish a baseline.

And the way they established a baseline

was a little bit unusual,

but will make perfect sense to you.

They had people wear long sleeves

and essentially cover up and avoid sunlight for a few days

so they could measure their baseline hormones

in the absence of getting a lot of UVB light exposure

from the sun or from other sources.

Now, of course, these people had access

to artificial lights,

but as I've pointed out on this podcast before,

it's pretty unusual that you'll get enough UVB exposure

from artificial lights throughout the day.

And in the morning you need a lot of UVB exposure,

or we should be getting a lot of UVB exposure to our eyes

and to our face and to our skin throughout the day,

provided we're not getting sunburnt.

This is actually a healthy thing for mood and for energy

throughout the day.

It's only at night, basically between the hours

of about 10:00 pm and 4:00 am,

that even a tiny bit of UVB exposure from artificial sources

can mess us up in terms of our sleep

and our energy levels, and so on.

And that's because of the potent effect of UVB

on suppressing melatonin.

So the point here is that they establish a baseline

whereby people were getting some artificial light exposure

throughout the day,

but they weren't getting outside a lot.

They weren't getting a lot of sunlight.

And then they had people receive a dose

of UVB light exposure

that was about 20 to 30 minutes outdoors.

They had people wear short sleeves, no hat, no sunglasses.

Some people wore sleeveless shirts.

They encouraged people to wear shorts.

So they were indeed wearing clothing.

They were not naked.

And they were wearing clothing that was culturally

and situationally appropriate,

at least for the part of the world

where this study was done.

And they had people do that two or three times a week.

So in terms of a protocol

that you might export from this study,

basically getting outside for about 30 minutes,

two or three times a week in a minimum of clothing,

and yet still wearing enough clothing

that is culturally appropriate.

They were outside, they weren't sun bathing,

flipping over on their back and front.

They were just moving about doing things.

They could read, they could talk,

they could go about other activities,

but they weren't wearing a broad brim hat

or a hat of any kind,

just getting a lot of sun exposure to their skin.

They did this for a total of 10 to 12 UVB treatments.

So this took several weeks, right?

It took about a month, if you think about it,

two or three times per week

for a total of 10 to 12 UVB treatments.

These treatments, of course, are just being outside

in the sun.

And then they measured hormones,

and they measured the psychology

of these male and female adult subjects.

Let's first look at the psychological changes

that these human subjects experienced

after getting 10 to 12 of these UVB light exposure

outdoor and sunlight type treatments.

They did this by collecting blood samples

throughout the study,

and they saw significant increases

in the hormones, beta-estradiol,

which is one of the major forms of estrogen,

progesterone, another important steroid hormone,

and testosterone in both men and women.

Now, an important point is that the testosterone increases

were significantly higher in men that happened to originate

from countries that had low UV exposure

compared to individuals from countries

with high UV exposure.

Now, this ought to make sense

if we understand a little bit

about how the skin functions as an endocrine organ.

Many of you have probably heard of vitamin D3,

which is a vitamin that we all make.

Many people supplement it as well

if they need additional vitamin D3.

We all require sunlight in order to allow vitamin D3

to be synthesized and perform its roles in the body.

And it turns out that people who have darker skin

actually need more vitamin D3 and/or more sunlight exposure

in order to activate that D3 pathway,

than do people with paler skin.

And this should make sense to all of you

given what you now understand about melanocytes,

that cell type that we discussed earlier,

because melanocytes have pigment within them.

And if you have darker skin,

it means that you have more melanocytes

or that you have melanocytes

that are more efficient at creating pigment.

And as a consequence,

the light that lands on your skin

will be absorbed by those melanocytes,

and less of it is able to impact the D3 pathway.

Whereas if you have pale skin,

more of the light that lands on your skin

can trigger the synthesis

and assist the actions of vitamin D3.

Similarly, in this study, they found

that people who had paler skin

and/or who originated from countries

where they had less UVB light exposure across the year

had greater, meaning more significant, increases

in testosterone overall

than did people who already were getting a lot

of UVB exposure.

This led them to explore so-called seasonal changes

in testosterone that occurred normally

in the absence of any light exposure treatment.

So up until now, I've been talking about the aspects

of this study involving people getting outside

for about 20 to 30 minutes per day in sunlight,

in a minimum of clothing.

There was an increase in testosterone observed

in both men and women.

The increases in testosterone were greater

for people that had paler skin than darker skin.

So the data I'm about to describe

also come from this same paper, but do not involve

20 to 30 minute daily sun exposure protocols.

It's simply addressing whether or not testosterone levels

change as a function of time of year.

They measure testosterone across the 12-month calendar.

This study was done on subjects living

in the Northern Hemisphere for the entire year.

And so in the months of January, February, and March,

of course, the length of days is shortest

and the length of nights is longest.

And, of course, in the spring and summer months,

June, July, August, September, and so on,

the days are much longer and the nights are shorter.

And what they observed was very obvious.

They observed that testosterone levels

were lowest in the winter months

and were highest in the months

of June, July, August, and September.

Now, these are very important data.

At least to my knowledge,

these are the first data systematically exploring the levels

of sex steroid hormones in humans

as a function of time of year

and thereby as a function

of how much sunlight exposure they're getting.

And what's remarkable about these data

is that they map very well to the data in mice

and the other data in this paper on humans,

which illustrate that if you're getting more UVB exposure,

your testosterone levels are higher.

This study went a step further

and explored whether or not the amount of sunlight exposure

that one is getting to their skin

influences their psychology

in terms of whether or not they have increased desire

to mate and so on.

It's well known that sunlight exposure

to the eyes can increase mood.

And I talked about this in the podcast episode

with my guest, Dr. Samer Hattar,

who's the director of the chronobiology unit

at the National Institutes of Mental Health.

And Samer's recommendation

is that people get as much bright light exposure

as they safely can in the morning and throughout the day

for sake of both sleep and energy,

but also for enhancing mood and regulating appetite.

In this study, it was found

that both males and females had higher levels

of romantic passion after getting the UV treatment.

In fact, some of them reported increases in romantic passion

from just one or two of these UV treatments.

So they didn't have to go through all 10 or 12 in order

to get a statistically significant increase in passion.

Now, when we talk about passion,

as the authors of this paper acknowledge,

there's really two forms.

There is emotional and sexual,

and they parse this pretty finely.

I don't want to go into all the details,

and we can provide a reference and link to this study

if you'd like to look at those details.

But what they found was that women

receiving this UVB light exposure

focused more on increases

in physical arousal and sexual passion,

whereas the men actually scored higher

on the cognitive dimensions of passion,

such as obsessive thoughts about their partner and so on.

Regardless, both males and females

experienced and reported a increase in sexual passion

and desire to mate.

And we now know there were increases

in testosterone and estrogen,

which of course could be driving the psychological changes,

although I'm sure that those interact in both directions,

meaning the hormones no doubt affect psychology

and no doubt the psychology,

these changes in passionate feelings,

no doubt also increased

or changed the hormone levels as well.

And I want to reemphasize

that there was a component of the study

that had no deliberate daylight, sunlight exposure

for 20 or 30 minutes,

but rather just looked at hormone levels throughout the year

and found that the increase in day length

correlated with increases

in testosterone and sexual passion.

Now, in my opinion, this is a very noteworthy study

because it really illustrates that sunlight and day length

can impact the melatonin pathway

and thereby take the foot off the brake,

so to speak, on testosterone, estrogen,

and the desire to mate.

It also emphasizes that sunlight, UVB light,

can directly trigger hormone pathways

and desire to mate and mating behavior.

Now, this study went a step further

in defining the precise mechanism

by which light can impact all these hormones

and this desire to mate.

And here, understanding the mechanism is key

if you want to export a particular protocol

or tool that you might apply.

We talked earlier about how UVB light exposure to the eyes

triggers activation of these particular neurons

within the eye,

and then with centers deeper in the brain,

and eventually the pineal gland

to suppress the output of melatonin

and thereby to allow testosterone and estrogen

to exist at higher levels

because melatonin can inhibit testosterone and estrogen.

In this study,

they were able to very clearly establish

that it is sunlight exposure to our skin

that is causing these hormone increases

that they observed in mice and humans.

And the way they did that

was to use the so-called knockout technology,

the ability to remove specific genes

within specific tissues of the body.

And what they found is that UVB light,

meaning sunlight-exposed skin,

upregulated, meaning increased the activity

of something called p53,

which is involved in the maturation of cells

and various aspects of cellular function.

And the cells they were focused on were the keratinocytes,

which you are now familiar with from our earlier discussion

about the fact that the epidermis of your skin

contains mainly keratinocytes and melanocytes.

Sunlight exposure increased p53 activity in the skin.

And p53 activity was required for the downstream increases

in ovarian size, in testicular size,

in testosterone increases, in the estrogen increases,

and the various other changes

that they observed at the physiological level

when animals or humans were exposed to sunlight.

So these data are important because what they mean

is that not only is it important

that we get sunlight exposure early in the day

and throughout the day to our eyes,

at least as much as is safely possible,

but that we also need to get UVB sunlight exposure

onto our skin if we want to activate this p53 pathway

in keratinocytes and the testosterone and estrogen increases

that are downstream of that p53 pathway.

So even though the gene knockout studies were done on mice,

they clearly show that if you remove p53 from the skin,

that these effects simply do not occur.

So in terms of thinking about a protocol

to increase testosterone and estrogen,

mood and feelings of passion,

the idea is that you would want

to get these two to three exposures per week,

minimum of 20 to 30 minutes of sunlight exposure

onto as much of your body

as you can reasonably expose it to.

And when I say reasonably, I mean,

of course you have to obey cultural constraints,

decency constraints.

And of course you have to also obey the fact

that sunlight can burn your skin.

So many people are probably going to ask,

"What happens if you wear sunscreen?"

Well, in theory, because sunscreen has UV protection,

it would block some of these effects.

Now I'm not suggesting

that people do away with sunscreen entirely.

I do hope to do an episode all about sunscreen in the future

because sunscreen is a bit of a controversial topic.

Skin cancers are a real thing,

and many people are especially prone to skin cancer,

so you need to take that seriously.

Some people are not very prone to skin cancers

and can tolerate much more sun exposure.

You're probably familiar with the simple fact

that if you've gone outside on the beach with friends,

some people get burned very easily, others don't.

So you really should prioritize the health

and the avoidance of sunburn on your skin.

However, these data and other data point to the fact

that we should all probably be striving

to get more sunlight exposure onto our skin

during the winter months

and still getting sunlight exposure onto our skin

in the summer months,

provided we can do that without damaging our skin.

Another set of very impressive effects of UVB light,

whether or not it comes from sunlight

or from an artificial source,

is the effect of UVB light on our tolerance for pain.

It turns out that our tolerance for pain

varies across the year

and that our pain tolerance is increased

in longer day conditions.

And as we saw with the effects of UVB

on hormones and mating,

again, this is occurring via UVB exposure to the skin

and UVB exposure to the eyes.

I want to just describe two studies

that really capture the essence of these results.

I'm going to discuss these in kind of a top contour fashion.

I won't go into it as quite as much depth

as I did the last study,

but I will provide links to these studies as well.

The first study is entitled

Skin Exposure to Ultraviolet B Rapidly Activates

Systemic, Neuroendocrine, and Immunosuppressive Responses.

And you might hear that and think,

"Oh, immunosuppressive that's bad."

But basically what they observed is that even one exposure

to UVB light changed the output of particular hormones

and neurochemicals in the body,

such as corticotropin hormone and beta-endorphins,

which are these endogenous opioids.

We've all heard of the opioid crisis,

which is people getting addicted to opioids

that they are taking in drug form, pharmaceuticals.

But here I'm referring to endorphins

that our body naturally manufactures and releases

in order to counter pain

and act as somewhat of a psychological soother also,

because, of course, physical pain and emotional pain

are intimately linked in the brain and body.

What they found was that exposure to UVB light

increased the release of these beta-endorphins.

It caused essentially the release

of an endogenous pain killer.

Now, a second study that came out very recently,

just this last week, in fact,

published in the journal Neuron,

Cell Press journal, excellent journal,

is entitled A Visual Circuit Related

to the Periaqueductal Gray Area

for the Antinociceptive Effects of Bright Light Treatment.

I'll translate a little bit of that for you.

The periaqueductal gray is a region of the mid-brain

that contains a lot of neurons

that can release endogenous opioids,

things like beta-enkephalin, things like enkephalin,

things like mu opioid.

These are all names of chemicals

that your body can manufacture

that act as endogenous pain killers

and increase your tolerance for pain.

They actually make you feel less pain overall

by shutting down some of the neurons

that perceive pain or by reducing their activity.

Not to a dangerous level, right?

They're not going to block the pain response

so that you burn yourself unnecessarily

or harm yourself unnecessarily,

but they act a bit of a pain killer from the inside.

If you heard the word antinociceptive,

nociception is basically the perception or the way

in which neurons respond to painful stimuli.

So you can think of nociceptive events

in your nervous system as painful events.

And there I'm using a broad brush.

I realized that the experts in pain will say,

"Oh, it's not really a pain circuit,"

et cetera, et cetera.

But for sake of today's discussion,

it's fair to say that nociception is the perception of pain.

So if this title is A Visual Circuit Related

to the Periaqueductal Gray,

which is this area that releases these endogenous opioids

for the antinociceptive, the anti-pain effects

of bright light treatment,

the key finding of this study

is that it is light landing on the eyes and captured

by the specific cells I was talking about earlier,

those intrinsically photosensitive melanopsin ganglion cells

is the long name for them,

but these particular neurons in your eye,

and in my eye incidentally,

that communicate with particular brain areas.

These brain areas have names.

If you want to know them, for you aficionados

or for you ultra curious folks,

they have names like the ventral lateral geniculate nucleus

and the intergeniculate leaflet.

The names don't matter.

The point is that light landing on the eyes

is captured by these melanopsin cells.

They absorb that light,

translate that light into electrical signals

that are handed off to areas of the brain,

such as the ventral geniculate.

And then the ventral geniculate communicates

with this periaqueductal gray area

to evoke the release of these endogenous opioids

that soothe you and lead to less perception of pain.

This is a really important study

because it's long been known that in longer days

or in bright light environments,

we tolerate emotional and physical pain better.

Previous studies had shown

that it is light landing on our skin

that mediates that effect, but only in part.

It couldn't explain the entire effect.

This very recent study indicates

that it's also light arriving at the eyes,

and in this case, again, UVB light, ultraviolet blue light

of the sort that comes from sunlight,

that is triggering these anti-pain

or pain-relieving pathways.

So once again, we have two parallel pathways.

This is a theme you're going to hear

over and over and over again, not just in this episode,

but in all episodes of the Huberman Lab Podcast,

because this is the way that your brain and body are built.

Nature rarely relies on one mechanism

in order to create an important phenomenon,

and pain relief is an important phenomenon.

So we now have at least two examples of the potent effects

of UVB light exposure to the skin and to the eyes.

One involving activation of testosterone

and estrogen pathways, as it relates to mating,

and another that relates to reducing the total amount

of pain that we experience

in response to any painful stimuli.

So for those of you that are thinking tools and protocols,

if you're somebody who's experiencing chronic pain,

provided you can do it safely,

try to get some UVB exposure, ideally from sunlight.

I think the 20 to 30-minute protocol,

two or three times per week is an excellent one,

seems like a fairly low dose of UVB light exposure.

It's hard to imagine getting much damage to the skin.

Of course, if you have very sensitive skin,

or if you live in an area of the world

that is very, very bright

and has intense sunlight at particular times of year,

you'll want to be cautious.

Heed the warnings and considerations about sunscreen

that I talked about earlier, or about wearing a hat.

But the point is very clear.

Most of us should be getting more UVB exposure

from sunlight.

I can already hear the screams within the comments

or rather the questions within the comments, saying,

"Well, what if I live in a part of the world

where I don't get much UVB exposure?"

And I want to emphasize something that I've also emphasized

in the many discussions on this podcast

related to sleep and circadian rhythms and alertness,

which is even on a cloud-covered day,

you are going to get far more light energy, photons

through cloud cover than you are going to get

from an indoor light source, an artificial light source.

I can't emphasize this enough.

If you look outside in the morning

and you see some sunlight,

if you see some sunlight throughout the day,

you would do yourself a great favor

to try and chase some of that sunlight

and get into that sunlight to expose your eyes

and your skin to that sunlight as much as you safely can.

And when I say as much as you safely can,

never ever look at any light,

artificial, sunlight, or otherwise,

that's so bright that it's painful to look at.

It's fine to get that light

arriving on your eyes indirectly.

It's fine to wear eyeglasses or contact lenses.

In fact, if you think about the biology of the eye

and the way that those lenses work,

that you will just serve to focus that light

onto the very cells that you want those light beams

to be delivered to,

whereas sunglasses that are highly reflective

or trying to get your sunlight exposure

through a windshield of a car

or through a window simply won't work.

I'm sorry to tell you,

but most windows are designed to filter out the UVB light.

And if you're somebody who's really keen on blue blockers

and you're wearing your blue blockers all day,

well, don't wear them outside.

And in fact, you're probably doing yourself a disservice

by wearing them in the morning and in the daytime.

There certainly is a place for blue blockers

in the evening and nighttime,

if you're having issues with falling and staying asleep.

But if you think about it, blue blockers,

what they're really doing

is blocking those short wavelength, UVB wavelengths of light

that you so desperately need to arrive at your retina

and of course, also onto your skin

in order to get these powerful biological effects

on hormones and on pain reduction.

And in terms of skin exposure,

these data also might make you think a little bit

about whether or not you should wear short sleeves

or long sleeves,

whether or not you want to wear shorts or a skirt or pants.

It's all going to depend on the context of your life

and the social and other variables

that are important, of course.

I don't know each and every one of your circumstances,

so I can't tell you to do X or Y or Z, nor would I,

but you might take into consideration

that it is the total amount of skin exposure

that is going to allow you to capture more or fewer photons,

depending on, for instance,

if you're completely cloaked in clothing

and you're just exposed in the hands, neck, and face

such as I am now,

or whether or not you're outside in shorts and a T-shirt,

you're going to get very, very different patterns

of biological signaling activation

in those two circumstances.

Many of you I'm guessing are wondering

whether or not you should seek out UVB exposure

throughout the entire year or only in the summer months.

And that's sort of going to depend

on whether or not you experience depression

in the winter months,

so called seasonal effective disorder.

Some people have mild, some people have severe forms

of seasonal effective disorder.

Some people love the fall and winter and the shorter days.

They love bundling up. They love the leaves.

They love the snow, they love the cold,

and they don't experience those psychological lows.

So it varies tremendously.

And there are genetic differences

and birthplace origin differences that relate to all this,

but really it has to be considered on a case-by-case basis.

I personally believe, and this was reinforced

by the director of the chronobiology unit

at the National Institutes of Mental Health, Samer Hattar,

that we would all do well to get more UVB exposure

from sunlight throughout the entire year,

provided we aren't burning our skin

or damaging our eyes in some way.

In addition to that, during the winter months,

if you do experience some drop in energy

or increase in depression or psychological lows,

it can be very beneficial to access a SAD lamp.

Or if you don't want to buy a SAD lamp,

'cause oftentimes they can be very expensive,

you might do well to simply get a LED lighting panel.

I've described one before.

And I want to emphasize that I have no affiliation whatsoever

to these commercial sources,

but I've described one before and I'll describe it again.

And we can provide a link to a couple examples of these

in the show, in the show note captions, excuse me.

This is a 930 to 1,000 lux, L-U-X, light source

that's designed for drawing.

It's literally a drawing box.

It's a thin panel. It's about the size of a laptop.

Very inexpensive compared to the typical SAD lamp.

I actually have one,

and I position it on my desk all day long.

I also happen to have skylights above my desk.

I'm fairly sensitive to the effects of light.

So in longer days I feel much better

than I do in shorter days.

I've never suffered

from full-blown seasonal effective disorder,

but I keep that light source on throughout the day

throughout the year.

But I also make it a point to get outside and get sunlight

early in the morning and several times throughout the day.

And if it's particularly overcast outside

or there just doesn't seem to be a lot of sunlight

coming through those clouds,

I will try to look at that light source

a little bit more each day

in order to trigger these mechanisms.

Now, some people may desire to get UVB exposure

to their skin and they want to do that

through sources other than sunlight.

And there it's a little bit more complicated.

There are, of course, tanning salons,

which basically are beds of UVB light.

That's really all they are.

I've never been to one.

I know people do frequent them

in certain parts of the world.

There, of course, people are covering their eyes.

They are only getting UVB exposure to their skin, typically

because the UVB exposure, or intensities rather,

tend to be very, very high.

And so you can actually damage your eyes.

If you're looking at a very, very bright

artificial UVB source up close.

So you really have to explore these options for yourself.

Sunlight of course, being the original

and still the best way to get UVB exposure.

So without knowing your particular circumstances, finances,

genetics, or place of origin, et cetera,

I can't know whether or not

you need to use artificial sources.

You're going to have to gauge that.

Meanwhile, getting outside, looking at

and getting some exposure of UVB onto your skin

is going to be beneficial

for the vast majority of people out there.

And in fact, it's even going to be beneficial

for people that are blind.

People that are blind, provided they still have eyes,

often maintain these melanopsin cells.

So even if you're low vision or no vision,

getting UVB exposure to your eyes

can be very beneficial for sake of mood,

hormone pathways, pain reduction, and so forth.

A cautionary note, people who have retinitis pigmentosa,

macular degeneration, or glaucoma,

as well as people who are especially prone to skin cancers

should definitely consult with your ophthalmologist

and dermatologist before you start increasing

the total amount of UVB exposure

that you're getting from any source, sunlight or otherwise.

There are additional, very interesting and powerful effects

of UVB light, in particular on immune function.

All the organs of our body are inside our skin.

And so information about external conditions,

meaning the environment that we're in,

need to be communicated to the various organs of our body.

Some of them have more direct access

to what's going on outside.

So for instance, the cells in your brain

that reside right over the roof of your mouth,

your hypothalamus, they control hormone output,

and they control the biological functions

that we call circadian functions,

the ones that change every 24 hours.

Well, those are just one or two connections,

meaning synapses away from those cells in your eye

that perceive UB, UVB light, excuse me.

Other organs of your body, such as your spleen,

which is involved in the creation of molecules

and cells that combat infection,

well, those are a long ways away

from those cell in your eye.

And in fact, they're a long ways away from your skin.

There are beautiful studies showing

that if we get more UVB exposure from sunlight

or from appropriate artificial sources,

that spleen and immune function are enhanced,

and there's a very logical,

well-established circuit as to how that happens.

Your brain actually connects to your spleen.

Now, it's not the case that you can simply think,

"Okay, spleen, turn on, release killer cells,

go out and combat infection."

However, UVB light arriving on the eyes

is known to trigger activation of the neurons

within the so-called sympathetic nervous system.

These neurons are part of the larger thing

that we call the autonomic nervous system,

meaning it's below or not accessible by conscious control.

It's the thing that controls your heartbeat,

controls your breathing and that also activates

or flips on the switch of your immune system.

When we get a lot of UVB light in our eyes,

or I should say sufficient UVB light in our eyes,

a particular channel, a particular set of connections

within the sympathetic nervous system is activated,

and our spleen deploys immune cells and molecules

that scavenge for and combat infection.

So if you've noticed that you get fewer colds and flus

and other forms of illness in the summer months,

part of that could be because of the increase in temperature

in your environment,

because typically longer days are associated

with more warmth in your environment

as opposed to winter days,

which are short when it tends to be colder out.

Well, that's true, but it's also the case

that people around you have fewer colds and flus

and that you will get infected with fewer colds and flus

and other infections, because if those infections,

whether or not they're bacterial or viral,

arrive in your body, right, if you inhale them

or they get into your mouth or on your skin,

your spleen meets those infections with a greater output.

In other words, the soldiers of your immune system,

the chemicals and cell types of your immune system

that combat infection

are in a more ready, deployed stance, if you will.

If you want to know more about the immune system

and immune function,

I did an entire episode about the immune system

and the brain, you can find that at hubermanlab.com.

We talk about cytokines,

we talk about killer cells, B cells, T cells, et cetera,

a lot of detail there.

So we often think about the summer months

and the spring months as fewer infections floating around.

But in fact, there aren't fewer infections floating around.

We are simply better at combating those infections,

and therefore there's less infection floating around.

So we are still confronted with a lot of infections.

We're just able to combat them better.

What does this mean in terms of a tool?

What it means is that during the winter months,

we should be especially conscious of accessing UVB light

to enhance our spleen function,

to make sure that our sympathetic nervous system

is activated to a sufficient level

to keep our immune system deploying all those killer T cells

and B cells and cytokines

so that when we encounter the infections,

as we inevitably will, right,

we're constantly being bombarded with potential infections,

that we can combat those infections well.

And as just a brief aside,

but I should mention, a brief aside

that's related to tens of thousands of quality studies,

it is well known that wound healing is faster

when we are getting sufficient UVB exposure.

Typically, that's associated with the longer days

of spring and summer.

It is known that turnover of hair cells,

the very cells that give rise to hair cells

are called stem cells.

They live in little so-called niches in our skin

with these hair stem cells,

and your hair grows faster in longer days.

That too is triggered by UVB exposure,

not just to the skin, but to the eyes.

That's right.

There was a study published

in the Proceedings of the National Academy of Sciences

a couple of years ago that showed that the exposure

of those melanopsin ganglion cells in your eyes

is absolutely critical for triggering the turnover

of stem cells in both the skin and hair,

and also turns out in nails.

So if you've noticed that your skin,

your hair and your nails look better and turn over more,

meaning grow faster in longer days,

that is not on a coincidence.

That is not just your perception.

In fact, hair grows more, skin turns over more,

meaning it's going to look more youthful.

You're going to essentially remove older skin cells

and replace them with new cells,

and all the renewing cells and tissues of our body

are going to proliferate,

are going to recreate themselves more

when we're getting sufficient UVB light to our eyes

and also to our skin.

And so while some of you may think of light therapies

such as red light therapies or UVB therapies

as kind of new agey, or just biohacking,

again, a phrase I don't particularly like,

this notion of biohacking,

'cause it implies using one thing for a purpose

that it was never tended to have,

well, it turns out that UVB exposure and red light,

as we'll soon see, is a very potent form

of increasing things like wound healing and skin health

for very logical mechanistically backed reasons.

So while I can't account for everything

that's being promoted out there

in terms of this light source

will help your skin look more youthful

or will help heal your scars,

the mechanistic basis for light having those effects

makes total sense.

But what you should consider, however,

is that if the particular light therapy

that you're considering involves very local application

rather than illuminating broad swaths of skin,

and if it has no involvement with the eyes,

meaning there's no delivery of UVB or red light

or the other light therapy to the eyes,

it's probably not going to be as potent a treatment

as would a more systemic activation

of larger areas of skin and the eyes.

Now, again, a cautionary note,

I don't want people taking technologies that were designed

for local application and beaming those into the eyes.

That could be very, very bad

and damaging to your retinal and other tissues.

Certainly, wouldn't want you taking bright light

of very high intensity of any kind

and getting cavalier about that.

Typically, the local illumination of say a wound

or a particular patch of acne

or some other form of skin treatment

involves very high intensity light.

And if the intensity is too high,

you can actually damage that skin.

And so as we'll talk about in a few moments,

most of those therapies for modifying skin

involve actually burning off a small, very thin layer

at the top of the epidermis

in efforts to trigger the renewal

or the activation of stem cells

that will replenish that with new cells.

So there's a fine line to be had between light therapies

that are very localized and intense,

which are designed to damage skin

and cause reactivation of new stem cells,

whether that's hair cells or skin cells, et cetera,

versus systemic activation across broad swaths of skin

and the eyes.

You really have to consider this on a case-by-case basis,

but at least for now just consider

that increases in hormones, reduction in pain

by way of increases in enkephalin

and other endogenous opioids,

improving immune status by activating the spleen,

and so on, and so on

really are all the downstream consequence

of illuminating large swaths of skin

and making sure that those neurons within the eye

get their adequate UVB exposure

or other light wavelength exposure,

not simply beaming a particular wavelength of light

at a particular location on the body

and hoping that that particular illumination

at a particular location on the body

is going to somehow change the biology at that location.

Our biology just really doesn't work that way.

It's possible, but in general,

systemic effects through broad scale illumination

and illumination to the eye,

combined with local treatments are very likely

to be the ones that have the most success.

Now, I'd like to shift our attention

to the effects of light on mood more specifically.

We talked about this

in terms of seasonal effective disorder,

but many of us don't suffer

from seasonal effective disorder.

So I'd like to drill a little deeper

into how light impacts mood.

And here, I want to, again, paraphrase the statements

of Dr. Samer Hattar

at the National Institutes of Mental Health,

I should mention the director of the chronobiology unit

at the National Institutes of Mental Health

and perhaps one of the top one to two to three world experts

in how light can impact mood, appetite,

circadian rhythms, and so forth.

Samer stated on the podcast,

and he said in various other venues as well,

that getting as much UVB light in our eyes and on our skin

in the early day and throughout the day

as is safely possible is going to be beneficial for mood.

There's also another time of day,

or rather I should say a time of night

in which UVB can be leveraged in order to improve mood,

but it's actually the inverse of everything

we've been talking about up until now.

We have a particular neural circuit that originates

with those melanopsin cells in our eye

that bypass all the areas of the brain

associated with circadian clocks,

so everything related to sleep and wakefulness,

that's specifically dedicated to the pathways

involving the release of molecules like dopamine,

the neuromodulator that's associated with motivation,

with feeling good, with feeling like there's possibility

in the world, and so on and so forth,

and other molecules as well,

including serotonin and some of those endogenous opioids

that we talked about before.

That particular pathway involves a brain structure

called the perihabenular nucleus.

The perihabenular nucleus gets input

from the cells in the eye that respond to UVB light,

and frankly, to bright light of other wavelengths as well,

'cause as you recall, if a light is bright enough,

even if it's not UV or blue light,

it can activate those cells in the eye.

Those cells in the eye

communicate to the perihabenular nucleus.

And as it turns out, if this pathway is activated

at the wrong time of each 24-hour cycle,

mood gets worse, dopamine output gets worse,

molecules that are there specifically to make us feel good,

actually are reduced in their output.

So while UVB exposure in the morning and throughout the day

is going to be very important for elevating

and maintaining elevated mood,

avoiding UVB light at night is actually a way

in which we can prevent activation

of this eye to perihabenular pathway

that can actually turn on depression.

To be very direct and succinct about this,

avoid exposure to UVB light from artificial sources

between the hours of 10:00 pm and 4:00 am.

And if you're somebody who suffers from low mood

and overall has a kind of mild depression

or even severe depression,

of course, please see a psychiatrist,

see a trained psychologist, get that treated,

but you would do especially well to avoid UVB exposure

from artificial sources, not just from 10:00 pm to 4:00 am,

but really be careful about getting too much exposure to UVB

even in the late evening,

so 8:00 pm perhaps to 4:00 am.

I can't emphasize this enough,

that if you view UVB light,

you activate those neurons in your eye very potently.

And if those cells communicate to the perihabenular nucleus,

which they do,

you will truncate or reduce the amount of dopamine

that you release.

So if you want to keep your mood elevated,

get a lot of light, UVB light, throughout the day,

and at night, really be cautious about getting UVB exposure

from artificial sources.

Now let's say you're somebody who has no issues with mood.

You're just the happiest person all year long,

or maybe you just have subtle variations in your mood.

You feel great about that.

Turns out that you still want to be very careful

about light exposure

between the hours of 10:00 pm or so, and 4:00 am,

in fact, even during sleep.

There's a recent study that just came out

in the Proceedings of the National Academy of Sciences,

and it's entitled Light Exposure During Sleep

Impairs Cardiometabolic Function.

This is a very interesting study

where they took human subjects, young adults,

and having them sleep in rooms

that had different lighting conditions,

either dim light or slightly bright light.

Now, many people can't fall asleep in brightly lit rooms,

so they acknowledge this.

These were not very brightly lit rooms.

These were rooms that had just a little bit

of overhead room lighting, a hundred lux,

which is not very bright at all.

Or they had them sleep in a room that had very dim light,

which is less than three lux.

If you want to get a sense of how bright three lux is

versus a hundred lux,

I would encourage you to download the free app Light Meter.

I have no relationship to the app.

It's a pretty cool app, however.

I've used it for a long time,

where you can basically point your phone

at a particular light source, sun or otherwise,

and you just press the button

and it'll give you an approximate readout of lux,

which is the light intensity

that the phone happens to be staring out at

at that location.

It's not exact, but it's a pretty good

back-of-the-envelope measure of light intensity.

So these subjects were either sleeping in a very dim room,

three lux is very, very dim,

or a somewhat dim room, a hundred lux.

In this study, they measured things like melatonin levels.

They looked at heart rate,

they looked at measures of insulin and glucose management.

Now, in previous episodes,

I've talked about how glucose, blood sugar,

is regulated by insulin

because you don't want your glucose levels

to be too high, hyperglycemia, or too low, hypoglycemia.

And the hormone insulin is involved in sequestering

and shuttling glucose in the bloodstream.

Basically, how well you manage glucose in the bloodstream

can be indirectly measured by your insulin levels.

And it's well known that sleep deprivation

can disrupt glucose regulation by insulin.

However, in this study, subjects were sleeping

the whole night through.

It just so happens that some of the subjects were sleeping

in this very dimly lit room, three lux,

and other subjects were sleeping

in a somewhat dimly lit room, a hundred lux.

What's incredible about this study

is that both rooms were sufficiently dimmed

that melatonin levels were not altered in either case.

This is really key.

It's not as if one group experienced a lot of bright light

through their eyelids and others did not.

Melatonin levels were not disrupted.

And given how potently light can inhibit melatonin,

this speaks to the fact

that this very dim condition of three lux

and the somewhat dim condition of a hundred lux

was not actually perceived by the subjects

nor was it disrupting these hormone pathways.

They also looked at glucose responses.

They had people essentially take a fasting glucose test

in different conditions.

I won't go into all the details,

but here's what they found.

In healthy adults, even just one night of sleeping

in a moderately lit environment,

this hundred lux environment, caused changes,

increases in nighttime heart rate,

which means that the sympathetic nervous system

was overly active as compared to people

that slept in a completely dark

or in a very, very dimly lit room.

Decreases in heart rate variability,

and here I should point out that heart rate variability

or HRV is a good thing, we want heart rate variability.

So they saw increases in heart rate,

decreases in heart rate variability,

and increases in next morning insulin resistance,

which is an indication that glucose management is suffering.

So this is powerful.

The results of this study essentially indicate

that even just one night of sleeping the whole night through

in a dimly lit environment is disrupting the way

that our autonomic nervous system is functioning,

altering so called autonomic tone,

making us less relaxed is probably the best way

to describe it,

even though we are asleep,

disrupting the way

that our cardiometabolic function operates,

such that we have lower heart rate variability

and increased insulin resistance.

This is not a good thing for any of us to experience.

So while we've mainly been talking

about the positive effects of UVB light

and other forms of light,

now we have two examples.

One from the work of Hattar and colleagues

showing that UVB exposure via the perihabenula

can diminish the output of dopamine

and other molecules that make us feel good

if that UVB exposure is in the middle of the night

or late evening.

And now we have yet another study performed,

in this case, in humans,

indicating that even if we fall asleep

and sleep the whole night through,

if the room that we're sleeping in has too many lux,

too much light energy,

that light energy is no doubt going through the eyelids,

which it can, activating the particular cells

in the eye that trigger an increase

in sympathetic nervous system activation

and disrupting our metabolism.

And this study rests on a number of other recent studies

published in Cell, which is a superb journal,

and other journals, showing that during the course

of a healthy, deep night's sleep,

our body actually transitions

through various forms of metabolic function.

We actually experience ketosis-like states.

We experience glucogenesis.

We experience different forms of metabolism

associated with different stages of sleep,

not something that we're going into in depth

in this podcast, we will in a future podcast.

What this study shows is that light exposure even in sleep

is disrupting our autonomic, in this case,

the sympathetic arm of the autonomic nervous system

in ways that are disrupting metabolism, probably in sleep,

but certainly outside of sleep so that we wake up

and have our first meal of the day.

Or even if you're intermittent fasting,

you eat that first meal of the day,

if your sleep is taking place in an environment

that's overly illuminated,

well, that's disrupting your cardiac function

and your metabolism.

I've been talking a lot about UVB light,

which is short wavelength light.

So UV light, blue light,

maybe even some blue green light,

that's going to be short wavelength light.

Now, I'd like to shift our attention

to the other end of the spectrum,

meaning the light spectrum,

to talk about red light and infrared light,

which is long wavelength light.

Many so-called low level light therapies,

the acronym is LLLT, low level light therapies,

involve the use of red light and infrared light.

Sometimes, low level light therapies involve the use of UVB,

but more often than not these days,

when we hear LLLT, low level light therapy,

it's referring to red light

and near-infrared light therapies.

Low level light therapies have been shown to be effective

for a huge number of biological phenomenon

and medical treatments.

I can't summarize all of those now.

It would take me many, many hours.

It would be an effective episode for curing insomnia,

but it wouldn't inform you properly about the use of light

for your health.

Rather, I'd like to just emphasize

some of the top contour of those studies

and point out that for instance,

low level light therapy with infrared light

has been shown to be effective for the treatment of acne

and other sorts of skin lesions.

There have been some really nice studies actually

where they use subjects as their own internal control.

So people, believe it or not,

agreed to have half of their face

illuminated with red light or near-infrared light,

and the other half of their face serve as a control,

and to do that for several weeks at a time.

And you can see pretty impressive reductions

in skin lesions, reductions in scars from acne,

and reduction in acne lesions themselves,

meaning the accumulation of new acne cysts

with low level light therapy,

using red light and infrared light.

Sometimes however, there is a resistance of that acne

to the low level light therapy,

such that people will get an initial improvement,

and then it'll go away despite continuing the treatment.

So you're probably asking, or at least you should be asking,

how is it that shining red light on our skin

can impact things like acne and wound healing, et cetera?

Well, to understand that, we have to think back

to the beginning of the episode

where I described how long wavelength light,

such as red light and near-infrared light,

which is even longer than red light,

can pass through certain surfaces, including our skin.

So our skin has an epidermis, which is on the outside,

and the dermis, which is in the deeper layers.

Red light and infrared light can pass down

into the deeper layers of our skin,

where it can change the metabolic function

of particular cells.

So let's just take acne as an example.

Within the dermis, the deep layers of our skin,

we have what are called sebaceous glands

that actually make the oil that is present in our skin.

Those sebaceous glands are often nearby hair follicles.

So if you've ever had a infected hair follicle,

that's not a coincidence

that hair follicles tend to get infected.

Part of it is because there's actually a portal down

and around the hair follicle,

but the sebaceous gland is where the oil is created.

That is going to give rise to, for instance, acne lesions.

Also, in the dermis, in the deep layers of the skin,

are the melanocytes.

They're not just in the epidermis,

they're also in the deeper layers of the skin.

And you have the stem cells that give rise

to additional skin cells.

If the top layers of the epidermis are damaged,

those stem cells can become activated.

And you also have the stem cells

that give rise to hair follicles.

So by shining red light or near-infrared light

on a localized patch of skin,

provided that red light is not of such high intensity

that it burns the skin,

but is of sufficient intensity that it provides

just a little bit of damage to the upper layers of the skin,

the epidermis,

and that it triggers certain biological pathways

within the cells of the sebaceous gland

and the stem cells within the hair cell niche

and the stem cells in skin,

what happens is the top layers of the skin

are basically burned off by a very low level of burn

and/or the cells in the deeper layer

start to churn out new cells,

which go and rescue the lesion,

essentially clear out the lesion and replace that lesion

with healthy skin cells.

This does work in the context of wound healing,

getting scars to disappear.

It also works to remove certain patches of pigmentation.

There are sometimes cases

where people will get a red blotchiness

due to certain skin conditions

or some darker pigmentation that they want remove,

or that they need removed,

because it's a potential skin cancer threat.

Now, how is red light actually doing it

within the cells of the sebaceous gland,

the stem cells, et cetera?

Well, long wavelength light

can actually get deep into the skin,

I mentioned that before,

but can also get into individual cells

and can access the so-called organelles,

which I described at the beginning of the episode.

In particular, they can access the mitochondria,

which are responsible for producing ATP.

Now, the simple way to think about this

for sake of this discussion is that as cells age,

and in particular, in very metabolically active cells,

they accumulate what are called ROSs,

reactive oxygen species.

And as reactive oxygen species go up,

ATP energy production in those cells tends to go down.

It's a general statement,

but it's a general statement that in most cases is true.

There are some minor exceptions that don't concern us

that have to do with cell types different than the ones

that I'm talking about now.

So the way to think about this is that red light passes

into the deeper layers of the skin,

activates mitochondria, which increases ATP,

and directly or indirectly reduces

these reactive oxygen species.

These reactive oxygen species are not good.

We don't want them.

They cause cellular damage, cellular death.

And for the most part just inhibit the way

that our cells work.

So if you've heard of red light

or near-infrared light therapies

designed to heal skin or improve skin quality

or remove lesions,

or get rid of scars or unwanted pigmentation,

that is not pseudoscience, that is not woo science.

That is grounded in the very biology of how light interacts

with mitochondria and reactive oxygen species.

Some of you may also find it interesting to note

that some of the cream-based treatments

for acne, for instance,

like retinoic acid, Retin-A,

is actually a derivative of vitamin A.

And the pathway involving retinoic acid and vitamin A,

believe it or not,

is very similar to the natural biological pathway

by which photopigments in the eye convert light information

into biological changes within those cells.

So the key point here is that light

is activating particular pathways in cells

that can either drive death of cells

or can make those cells essentially younger

by increasing ATP

by way of improving mitochondrial function.

And in recent years, there have been some

just beautiful examples that exist,

not only in the realm of skin biology,

but in the realm of neurobiology whereby red light

and near-infrared light can actually be used

to enhance the function of the cells

that, for instance, allow us to see better

and indeed cells that allow us to think better.

So now I'd like to review those data

because not only are they interesting in their own right,

but they also point to some very interesting

and powerful application of low-cost or zero-cost tools

that we can use to improve our vision.

If you are somebody who's interested in the use of red light

or near-infrared light,

so-called LLLT, low level light therapies,

for treatment of dermatologic issues,

so anything related to skin,

I will include a link to a excellent set of reviews.

The first one is Light-emitting Diodes in Dermatology:

A Systematic Review of Randomized Controlled Trials.

That one includes review of a very large number of studies,

came out just a few years ago in 2018,

and I think is very clearly

and cleanly laid out for anyone to access.

And you can see the degree of effects

of red light, for instance,

on treatment of acne or scarring, et cetera.

And I'll also provide a link to another review,

which is Low-level Light Therapy in Skin:

Stimulating, Healing, and Restoring.

So for those of you that are interested, again,

in dermatologic issues

and the kind of restoring youthfulness

and the kind of general themes of anti-aging and longevity

and how red light therapies can be used for that,

I would encourage you to take a look at those reviews.

What you're going to find is that rarely, if ever,

is there a study looking at whole body

red light illumination

for sake of treating and improving skin.

And I mention this because I get a lot of questions

about infrared sauna and global illumination

with red lights.

We'll talk more about cases

where global illumination of your whole body

or your whole face with red lights might be useful,

but in terms of infrared sauna,

I've mentioned on this podcast before,

and I will certainly go deeper on this

in an upcoming episode,

all about the use of heat and temperature

for augmenting our biology,

but in general, infrared saunas don't get hot enough,

temperature-wise, in order to trigger some

of the important effects on growth hormone

and heat shock proteins and some of the other things

that sauna has been shown to be excellent for.

That's a general statement.

I realize there are some infrared saunas

that do get hot enough.

There are very few data on the use

of whole body illumination with infrared saunas

that really point to any specific

mechanistically supported effects.

Almost all the positive effects that you're going to see

of red light and low-level light therapies,

certainly the ones discussed in the reviews

that I just mentioned,

are going to be the consequence

of very directed illumination of particular patches of skin

that are seeking repair,

that people are seeking the repair of.

So again, I don't want to disparage infrared saunas,

but in general, they don't get hot enough

to trigger most of the positive effects

that sauna have been demonstrated to have.

And it's unclear at all as to whether or not

they can enhance skin quality, youthfulness,

restore top layers of skin that are damaged,

repair acne, et cetera.

So more on heat saunas and infrared saunas

and their comparison in an upcoming episode.

So let's talk about a clear set of examples

where red light and near-infrared light

have been shown to have positive effects on our health.

And these are the data that I referred to at the beginning

of the episode from Dr. Glen Jeffery

at University College London,

who, again, is a longstanding member