Sun exposure is linked to positive effects on brain function, but in order to quantify these benefits, you will just have to measure it for yourself.
Surely you are familiar with the warnings surrounding over-exposure to the sun and the potential danger of it's powerful UV rays. While we are constantly reminded by advertisements, doctors and worry-some parents to protect ourselves by wearing sunscreen, hats and clothing, we also know that sun exposure is essential to our well-being. Sunlight is required for us to produce Vitamin D, and low levels of this essential vitamin are correlated with numerous health problems, including autoimmune diseases, cancer, diabetes, cardiovascular disease, obesity, depression, and osteoporosis.
Most dermatologists argue that taking a supplement, rather than a sun bath, is a much safer and just as effective way to get your daily dose of Vitamin D while protecting yourself from skin cancer. However, we recently came across an interesting article that questions this claim. According to the article, Vitamin D in and of itself may not be the true source of the many protective health benefits often associated with it--it may just be a marker of the actual origin: sunshine.
In support of this theory, it has been found that UV exposure, independent of Vitamin D production, initiates the production of Nitric Oxide, which dilates blood vessels and thus lowers blood pressure. So while a high level of Vitamin D may not decrease your risk of a heart attack, it’s a good indication that you spend a lot of time in the sun, which decreases your blood pressure by way of increasing Nitric Oxide. If the body uses sunlight for both Vitamin D and Nitric Oxide production, it seems likely that it would use sunlight for other things as well.
Unsurprisingly, this idea got us thinking about the connection between sunlight exposure and brain function. Turns out, a recent article in Cell documents a newly-discovered biochemical pathway by which UV radiation positively impacts brain function in mice. This pathway is initiated by activation of urocanic acid, which has been known since at least 1967 to be a UV-absorbing compound in the skin. Additionally, presence of urocanic acid levels were already known to increase in the skin and blood following UV exposure, but the downstream neurological effects of this fact have not been previously explained.
The previously mentioned article published in Cell found that urocanic acid is able to cross the blood-brain barrier, where it is taken into neurons and promotes the production of glutamate. This pathway has been known to occur in the liver, but given the inability of glutamate to cross the blood brain barrier, production outside of the brain has no effect on cognitive function. The authors found that this urocanic acid-initiated glutamate production occurs in multiple brain regions, meaning that sun exposure has downstream effects on multiple neurological pathways. Sun exposure has previously been shown to have positive effects on mood, depression and bipolar disorder, but it’s yet to be determined if it is by way of this urocanic acid-glutamate pathway.
You might then be wondering, what role does glutamate play in your brain? As the most abundant of all excitatory neurotransmitters in vertebrates, it does a lot. Directly, glutamate is an key player in brain development, learning, memory, energy production, protein synthesis, plasticity, and modulating sleep (to name a few), all of which then have their own downstream effects. A recent review of the role of glutamate in sleep and how it relates to neurodegenerative diseases points out that a circadian rhythm disturbance due to dysfunction in the glutamate pathway is usually the first symptom of neurodegenerative diseases such as Alzheimer’s Disease. Glutamate can also be converted to the inhibitory neurotransmitter, GABA, whose role has been mentioned numerous times in previous posts (type GABA into the search box to read these posts).
Sun exposure is by no means the only way to get glutamate to your brain, but it is likely still an important one. The existence of the pathway was only published last year, so its full significance and specific details about it are likely still a long way off. However, it is something that you could easily investigate yourself with a Brain Gauge! Based on results from the Cell Article, increased glutamine becomes present in the brain within 2-3 hours of sun exposure. With this knowledge, you could take your Brain Gauge test, go outside in the sun, and then re-test 2-3 hours later, looking for any differences in your scores. You can also experiment with different durations of sun exposure. The mice in the experiment were exposed to 120 minutes of sunlight, variations in this duration of sun exposure was not tested, so you might investigate the optimum amount of time to spend in the sun. Another possibility is experimenting with the "wait" period of time between when you move out of the sun before your follow-up test (2-3 hours is just our best guess for a starting point). Experimenting at different times of the year will also give interesting results — changes in sun's intensity (you can check the UV index) and your skin's melanin levels will likely vary throughout the year and impact the amount of sunlight needed to see changes.
Of course, there’s no way to know for sure that any changes in brain function following sun exposure are due to elevated levels of glutamate in your brain, but if you find that sunlight does help your brain, does it really matter what the mechanism is? Knowing that the urocanic acid glutamate pathway exists is helpful because we know that there is at least one way sunlight effects our brains. On an individual level, knowing what changes you can make to optimize your personal brain health is much more important than knowing the exact science and mechanisms taking place. As we’ve noted before, even if this type of test was done on humans in a laboratory setting and published in a peer-reviewed journal, the results might not mean a whole lot to you, specifically. Everyone has different skin types, genetics, and other environmental factors, so the average effect of sunlight on a specific group of study participants would at best give you a general idea of how you would react to the specific treatment protocol used in the study.
Modern society often pushes the idea that we can be independent from our environment, but science is increasingly starting to recognize that we do, in fact, need nature, and can't be replaced by a bottle off the shelf. Sunlight provides us with many more benefits than just Vitamin D - it has also been shown that animals can use chlorophyll obtained through diet to capture sunlight and produce energy in the form of ATP, and that we have a physiological addictive response to sun exposure, probably to ensure we get enough of it! When you think about it, it would be weird if humans had evolved with the sun, an endless supply of free energy, and not taken advantage of it in some way. You still need to be smart about avoiding over-exposure and sun burns, but at the same time, you probably shouldn’t avoid direct sunlight altogether. So maybe we should take some advice from plants and be a little less scared of the sun and try to appreciate all of the benefits it has to offer!