Essentials: Using Light to Optimize Health

SAD lamps and LED panels can offset winter depression

Huberman explains that for people who experience seasonal affective disorder or energy drops in winter, a SAD lamp or an inexpensive LED lighting panel can be very beneficial, and shares that he keeps one on his desk throughout the year.

"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 oftentimes 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 affective 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 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 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."

Melatonin as the body's seasonal calendar system

Huberman describes how melatonin acts as a calendar system based on light, with more melatonin released in winter months than summer months, converting environmental light information into a signal that changes the internal environment of the body.

"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."

Avoiding bright light at night prevents depression pathways

Huberman reveals that exposure to bright light between 10 PM and 4 AM activates a specific eye-to-brain pathway that reduces dopamine output and can trigger depression, making nighttime light avoidance critical for mood.

"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-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 p.m. and 4 a.m."

UVB light exposure boosts immune function through the spleen

Huberman explains the circuit by which UVB light arriving on the eyes activates the sympathetic nervous system, which in turn causes the spleen to deploy immune cells and molecules, making us better at fighting infections in summer than winter.

"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 cytokines 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 ganglion 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."

UVB light exposure increases testosterone, estrogen, and pain tolerance

Huberman details how UVB light exposure to the skin for 20-30 minutes, two to three times per week, increases testosterone and estrogen levels and boosts pain tolerance through beta-endorphin release from skin cells called keratinocytes.

"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 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. If you're a regular listener of the Huberman Lab podcast, you've no doubt heard me talk about the vitamin mineral probiotic drink AG1."

UVB light between 10 PM and 4 AM suppresses dopamine and worsens mood

Huberman warns that UVB exposure at the wrong time activates the perihabenular nucleus, a pathway that suppresses dopamine and triggers depression-like symptoms, making timing of light therapy critical.

"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-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 p.m. and 4 a.m."