Using Light (Sunlight, Blue Light & Red Light) to Optimize Health | Huberman Lab Essentials

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

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

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

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

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

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

eyes. These photo receptors come in two major types. The so-called rods and the

major types. The so-called rods and the cones. The rods are very elongated. They

cones. The rods are very elongated. They

look like rods. And the cones look like little triangles. The other place of

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

epidermis. We have caratinosytes and we have melanocytes. With light exposure,

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

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

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

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

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.

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

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

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

cases. And melatonin can have a number of different effects, not just related to sleep. But that's supplemented

to sleep. But that's supplemented melatonin. Here I'm talking about our

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

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

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

taking melatonin. Most of the effects of melatonin on those functions are reversible. But I should point out that

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

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

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

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

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

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

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

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

threshold. They did not look at testes size or ovarian size in the human subjects. However, because they are

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

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

conditions. This is occurring via UVB exposure to the skin and UVB exposure to the eyes. I want to just describe two

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

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

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. 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

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

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

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,

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

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

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

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

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

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

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

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

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

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

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

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

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

happens. Your brain actually connects to your spleen. UVB light arriving on the

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

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

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

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

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

coincidence. That is not just your perception. In fact, hair grows more.

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

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

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

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

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

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

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

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

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

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

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

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

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

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 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

unwanted pigmentation. That is not pseudocience. That is not woo science.

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

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.

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

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,

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

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

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

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

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

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

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

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

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

way. I don't just say that to protect us. I say that to protect you, of

us. I say that to protect you, of course, because you are responsible for your health. And again, retinal neurons

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

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

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

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

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

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

perform. That's going to be your best guide. Today I covered what I would say

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

health. And as always, thank you for your interest in science.