Welcome to Huberman Lab Essentials,

where we revisit past episodes for the

most potent and actionable science-based

tools for mental health, physical

health, and performance.

I'm Andrew Huberman and I'm a professor

of neurobiology and opthalmology at

Stanford School of Medicine. Today we

are going to discuss light and the many

powerful uses of light to optimize our

health. 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. Light is

electromagnetic energy. 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. 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, etc. 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. 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 photo receptors in the back of our

eyes. These photo receptors 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. The other place of

course where light can impact our body

is on our surface on our skin. In the

top layer of skin which is called the

epidermis. We have caratinosytes and we

have melanocytes. 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. 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 is the spleen. Light will never

land directly on your spleen, but the

spleen still responds to light

information through indirect pathways.

Light arriving on the eyes

is absorbed by a particular cell type

called the intrinsically photosensitive

ganglen 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 ganglen cell, also called

the melanopsin cell, because it contains

an opsin, a photo pigment that absorbs

shortwavelength light that arrives

through sunlight. Those cells

communicate to particular stations in

the brain that in turn can connect to

your so-called pineal gland, which is

this little P-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. 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 365day calendar year. Indogenous

melatonin, meaning the melatonin that we

make within our bodies naturally, not

melatonin that's supplemented, has two

general categories of 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.

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 etc. 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 indogenous melatonin,

and that is healthy to keep them out of

puberty until it's the right time for

puberty to happen. 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. 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 your the different cells and

tissues and organs of your body are

working and that melatonin is the

transducer of that signal. 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 describe 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 the very

firmly established fact, which is that

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. 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, etc. And that is communicating

information about where your brain and

body should be in time. 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. 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.

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 paper that was published in the

journal cell reports, cell press

journal, excellent journal, 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 short wavelength 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 gonatal

weight, literally increases in testes

size and in ovarian size when mice were

exposed to this UVB light past a certain

threshold. They did not look at testes

size or ovarian size in the human

subjects. However, because they are

humans, they did address the psychology

of these human beings and address

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. 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. 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 this 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. 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. 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. The first study is

entitled skin exposure to ultraviolet B

rapidly activate systemic neuroendocrine

and immunosuppressive responses.

Basically what they observed is that

even one exposure to UVB light change

the output of particular hormones and

neurochemicals in the body such as

corticotropen hormone and betaendorphins

which are these endogenous opioids in

order to counter pain and act as a

somewhat of a psychological soother

also. What they found was that exposure

to UVB light increased the release of

these beta endorphins. Now a second

study published in the journal Neuron

cell press journal excellent journal is

entitled a visual circuit related to the

perryqueductal gray area for the

anti-nosceptive effects of bright light

treatment. I'll translate a little bit

of that for you. The perryqueductal gray

is a region of the midbrain that

contains a lot of neurons that can

release indogenous opioids. things like

beta eneopioid.

These are all names of chemicals that

your body can manufacture that act as

endogenous painkillers and increase your

tolerance for pain. They actually make

you feel less pain overall by shutting

down some of the neurons that perceive

pain. They're not going to block the

pain response so that you burn yourself

unnecessarily or harm yourself

unnecessarily, but they act as a bit of

a painkiller from the inside. The key

finding of this study is that it is

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 to evoke the

release of these indogenous opioids that

soothe you and lead to less perception

of pain. So for those of you that are

thinking tools and protocols, 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. 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. 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. 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,

they 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. 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. 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. 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, you know, exposed in

the hands, uh, 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. 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, Samaritar,

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

because often times they can be very

expensive. You might do well to simply

get a LED lighting panel. Very

inexpensive compared to the typical SAD

lamp. I actually have one and I position

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. 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 pigmentotosa, macular

degeneration or glaucoma, as well as

people who are especially prone to skin

cancers should definitely consult with

your opthalmologist 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

your body, such as your spleen, which is

involved in the creation of molecules

and cells that combat infection. 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

wellestablished circuit as to how that

happens. Your brain actually connects to

your spleen. 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. 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. 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. 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 cytoines so that

when we encounter the infections, as we

inevitably will, 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.

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

melanops and ganglin cells in your eyes

is absolutely critical for triggering

the turnover of stem cells in both the

skin and hair and also it 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 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. 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 and

other molecules as well including

serotonin and some of those indogenous

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 because 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.

Avoiding UVB light at night is actually

a way in which we can prevent activation

of this eye to perihabular 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 p.m. and 4:00 a.m. If you view UVB

light, you activate those neurons in

your eye very potently. And if those

cells communicate to the perihabular

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, I wouldn't

want people to become so neurotic about

UVB exposure that they won't flip on a

light at all. But you would do well, for

instance, to put any artificial lights

that you have on in the evening, kind of

low in your physical environment.

Because these melanopsin cells reside in

the lower half of our eyes, they view

the upper visual field. That makes sense

because they were designed to

essentially respond to sunlight coming

from above us

and try and dim those lights as far down

as you safely can. 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. 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, etc. To understand that, we

have to think back to the beginning of

the episode where I described how

longwavelength 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.

What happens is the top layers of the

skin are basically burned off by a very

low level of burn andor 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. 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 organels. In particular, they

can access the mitochondria which are

responsible for producing ATP. As cells

age, and in particular in very

metabolically active cells,

they accumulate what are called ROS's,

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. 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 cellar damage,

cellar 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

pseudocience. That is not woo science.

That is grounded in the very biology of

how light interacts with mitochondria

and reactive oxygen species. 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. And these are the data from Dr.

Glenn Jeffrey at University College

London who again is a long-standing

member of the neuroscience community

working on visual neuroscience and who

over the last decade or so has really

emphasized the exploration of red light

and near infrared light for restoration

of neuronal function as we age. The

Jeffrey Lab has published two studies in

recent years on humans that looked

directly at how red light and near

infrared light can improve visual

function. The Jeffrey Lab approached

these studies with that understanding of

how mitochondria and reactive oxygen

species and ATP work. And what they did

is they had people, subjects that were

either younger, so in their 20s, or 40

years old or older,

view red light of about 670 nanometers.

670 nanometers would appear red to you

and me. They had they had them do that,

excuse me, at a distance that was safe

for their eyes. So at about a foot away.

And they had them do that anywhere from

2 to 3 minutes per day. And in one study

they had them do that for a long period

of time of about 12 weeks. And in the

other study they had them do that just

for a couple of weeks. The major

findings were that in individuals 40

years old or older, so in the 40 to 72

year old bracket, but not in the

subjects younger than 40 years old. They

saw an improvement in visual function.

That improvement in visual function was

an improvement in visual acuity meaning

the ability to resolve fine detail and

using a particular measure of visual

function which is called the Triton exam

tr I tan Triton exam which specifically

addresses the function of the so-called

shortwavelength cones the ones that

respond to green and blue light they saw

a 22% improvement in visual acuity which

in the landscape of visual testing is an

extremely exciting result. As we age, we

tend to lose rods. We tend to lose other

cells within the retina, including the

cells that connect the eye to the brain,

the so-called ganglen cells. However,

because rods and cones, both are not

just among the most metabolically active

cells in your entire body, but the most

metabolically active cells in your

entire body. Those cells tend to

accumulate a lot of reactive oxygen

species as we age. Red light of the sort

used in these studies was able to reduce

the amount of reactive oxygen species in

the rods and cones and to rescue the

function of this particular cone type,

the short wavelength and medium

wavelength cones. The important takeaway

here is that viewing red light and near

infrared light at a distance at which it

is safe for just a couple of minutes

each day allowed a reversal of the aging

process of these neurons. So here we're

seeing a reversal of the aging process

in neurons by shining red light on those

neurons. So a little bit more about the

studies from the Jeffrey lab. One of the

things that they observed was a

reduction in so-called dusen duen.

Dusen are little fatty deposits, little

cholesterol deposits that accumulate in

the eye as we age. Our neural retina

being so metabolically active requires a

lot of blood flow. It's heavily

vascularized and dusen are a special

form of cholesterol that accumulate in

the eye. As it turns out, these red

light and near infrared light therapies

explored by the Jeffrey lab were able to

actually reduce or reverse some of the

accumulation of dusen. And so in

addition to reducing reactive oxygen

species, the idea in mind now is that

red light may actually reduce

cholesterol deposits and reactive oxygen

species in order to improve neuronal

function. So what should you and I do

with these results or should we do

anything with these results? Well, first

of all, I want to emphasize that even

though these studies are very exciting,

they are fairly recent and so more data

as always are needed. There's some

additional features of these studies

that I think are also important to

consider. First of all, the exposure to

red light needed to happen early in the

day, at least within the first 3 hours

of waking.

How would one do that? Well, nowadays

there are a number of different red

light panels and different red light

sources that certainly fall within the

range of red light and near infrared

light that one could use. So, if you're

somebody who wants to explore red light

therapy, here's what you need to do. You

need to make sure that that red light

source, it's not so bright that you're

damaging your eye. A good rule of thumb

is that something isn't painful to look

at. And in fact, I should just emphasize

that anytime you look at any light

source, sunlight or otherwise, that it's

painful and makes you want to squint or

close your eyes, that means it's too

bright to look at without closing your

eyes. Okay, that's sort of a duh, but I

would loathe to think that anyone would

harm themselves with bright light in any

way. I don't just say that to protect

us. I say that to protect you, of

course, because you are responsible for

your health. And again, retinal neurons

do not regenerate. Once they are gone

and dead, they do not come back. The

wavelength of light is important. It is

red light and near infrared light that

is going to be effective in this

scenario. The authors of this study

emphasized that it was red light of 670

nanometers in wavelength and near

infrared light of 790 nanometers in

wavelength that were effective and that

those wavelengths could be

complimentary. A lot of the commercially

available red light panels that you'll

find out there combine both red light

and near infrared light. However, I want

to emphasize that most of the panels

that are commercially available are

going to be too bright to safely look at

very close up. And in fact, that's why

most of those red light panels are

designed for illumination of the skin

and oftentimes arrive in their packaging

with eye protectors that are actually

designed to shield out all the red

light. So take the potential dangers of

excessive illumination of the eyes with

any wavelength of light seriously. But

if you're going to explore 670 and 790

nanometer light for sake of enhancing

neuronal function, set it at a distance

that's comfortable to look at and that

doesn't force you to squint or doesn't

make you feel uncomfortable physically

as if you need to turn away during the

period of that two to three minute

illumination each day. So the studies I

just described once again involve the

use of red light early in the day within

three hours of waking and are for the

sake of improving neuronal function. Red

light has also been shown to be

beneficial

late in the day and even in the middle

of the night. And when I say middle of

the night, I'm referring to studies that

explored the use of red light for shift

workers. I realize that many people are

doing shift work or they have to work

certainly past 10 p.m. or maybe they're

taking care of young children in the

middle of the night and they have to be

up. In that case, red light can actually

be very beneficial. And nowadays, there

are a lot of sources of red light

available just as red light bulbs. You

don't need a panel. So, what I'm

basically saying is that it can be

beneficial to use red lights at night.

The study I'd like to emphasize in this

context is entitled red light, a novel

non-farmacological intervention to

promote alertness in shift workers. The

takeaway from this study is very clear.

If you need to be awake late at night

for sake of shift work or studying or

taking care of children, etc., Red light

is going to be your best choice because

if the red light is sufficiently dim,

it's not going to inhibit melatonin

production and it's not going to

increase cortisol at night. Cortisol

should be high early in the day or at

least should be elevated relative to

other times of day if you are healthy. A

late shifted increase in cortisol,

however, 9M cortisol, 10 p.m. cortisol

is well known to be associated with

depression and other aspects of mental

health, rash, as a mental illness. So,

if you do need to be awake at night or

even all night, red light is going to be

the preferred light source. And in terms

of how bright to make it, well, as dim

as you can while still being able to

perform the activities that you need to

perform. That's going to be your best

guide. Today I covered what I would say

is a lot of information. My goal was to

give you an understanding of how light

can be used to change the activities of

cells, organels within those cells,

entire organs, and how that can happen

locally and systemically. So, thank you

once again for joining me today for this

deep dive discussion into

phototherapies, meaning the power of

light to modulate our biology and

health. And as always, thank you for

your interest in science.