Sun, sun, merciful one!
— Live

Human are diurnal creatures, which means that we're programmed to be awake while the sun is shining and sleeping at night. But while we can easily look at our smartphones to tell the time of day, our genes use a far more rudimentary input for time-keeping: The presence or absence of bright light.

Bright light (and particularly blue wavelength light, which the sun emits) has many effects on our bodies. Unfortunately today, our daytime exposure to sun is limited—we're frequently stuck in our apartments or sitting in cars, to get to our 9-to-5 desk jobs.

Here are 5 incredible health benefits of the sun that will hopefully inspire you to embrace the light of day.

1. It makes your brain work faster.

University of Arizona researchers recently exposed adult volunteers to bright blue light (mimicking the wavelength of sunlight) for 30 minutes, and then looked at their brain activity with an fMRI machine. Bright light exposure seemed to activate subjects' prefrontal cortex, the region of the brain responsible for "higher order" aspects of cognition including planning, decision making, and even aspects of personality. The light also seemed to sharpen their mental acuity: subjects displayed increased processing speed and reaction times on tests compared to those exposed to amber-colored light. (R)

2. It makes you horny baby, yeah.

A small trial involved 38 fellas who complained of both low libido and low sexual satisfaction. Half of the men were exposed to full spectrum light (to mimic sun exposure) for 30 minutes per day for 2 weeks. A placebo group was exposed to "sham" light for the same period. The men exposed to blue light showed a 3-fold improvement in subjective sexual function, along with a 70% increase in testosterone from baseline. (R) Shwing!

3. It reduces stress hormones.

Cortisol is the body's chief waking hormone, but it also can become chronically elevated due to stress. Chronically-elevated cortisol is no bueno—it can cause the accumulation of inflammatory visceral fat (that's the fat in your midsection that squeezes your organs), and shrink the memory center of your brain.

While finding appropriate means of dealing with stress (like meditation) is probably the best strategy, bright light exposure may help as well. When people were exposed to short wavelength (blue) light for 6.7 hours, their cortisol levels decreased by up to 25% compared to what they were at baseline. (R) Granted, spending 7 hours in daylight may seem a bit impractical today, but as hunter-gatherers, spending the whole day outside would be the norm. In fact, you could argue based on this research that spending the whole day indoors actually boosts cortisol 25%!

4. It makes you happier.

Serotonin, the neurotransmitter famous for its role in mood, is normally produced during the day, and darkness causes it to become converted to melatonin (this is why melatonin production is disrupted by bright light exposure at night). When scientists looked into the brains of people who'd died during both the summer and winter months, brain serotonin levels were higher in those who died in summer than in those who died in winter. (R) This may be why so many people are affected by Seasonal Affective Disorder, a dip in mood accompanying the shorter days of winter.

5. It protects you against nighttime screen exposure.

Technology is a double-edged sword. In many ways, it rules—you're reading this article thanks to it. In other ways, it is disruptive. One way that it has harmed our health is by exposing us to unprecedented amounts of blue light in the evening hours, when for hundreds of thousands of years our eyes would have only known amber-colored light (from fire) once the sun went down. This suppresses melatonin which is involved not just in healthy sleep but in healthy immune function. So, how can we continue to have our technology and eat it too?

In one small study from Japan, exposure to daytime blue light actually prevented light-induced melatonin suppression at night. (R) This suggests by going outside and getting your fill of blue light during the day, you can more safely make use of your devices at night.

6. It boosts your immune system.

Groundbreaking research out of Georgetown University found that blue light "activated" a category of immune cells called T cells and caused them to move around faster. (R) While this was an in vitro study (meaning it was done in a petri dish and not in a real, living body), blue wavelength light is able to penetrate the skin where it can reach these cells, which then circulate throughout the body. This suggests that the sun acts as a "hormetic" stimulus, creating a mild "stress" at the cellular level, which then activates gene pathways involved in protection and repair.

7. It regulates healthy gene expression (in a huge number of genes).

Imagine a little clock within each cell in your body. Exposure to bright light in the morning is what sets these clocks, called your circadian rhythm. This rhythm regulates 15% of the human genome including genes that regulate hormones that control appetite, immune function and produce neurotransmitters.

8. It may protect your eyes.

Nearsightedness is a growing problem around the world, but what if such a problem were optional for some? Higher UVB exposure, directly related to time outdoors and sunlight exposure, was associated with reduced odds of nearsightedness, and exposure to UVB rays between ages 14 and 29 years was associated with the highest reduction in odds of adult nearsightedness. (R)

9. It can make you live longer.

When researchers followed 29,518 Swedish women over 20 years, they found that those who had the most sun exposure had longer lives and less cardiovascular disease than those who avoided the sun. Compared to the most avid sunbathers, those who avoided the sun had reduced life expectancies of 0.6–2.1 years. In fact, cigarette smokers in the highest sun exposure group were at a similar risk of death and disease as non-smokers who avoided sun exposure—sun avoidance seemingly cancelled out the health benefits of not smoking! (R)

10. It helps you sleep better at night.

When people are exposed to sunlight or very bright artificial light in the morning, their nocturnal melatonin production occurs sooner, and they fall asleep more easily at night. (R) Sleep is a master hormonal regulator, and as such may help you to attain greater willpower when it comes to dietary choices. See? Everything's connected!

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