 If one is going to make an evolutionary argument for what a natural vitamin D level might be, how about getting vitamin D in the way nature intended sun instead of supplements? Let's run through the pros and cons. Though supplements may only cost about $10 a year, sunlight is free. You never have to worry about getting too much vitamin D from sunlight, because your body has a way to regulate production in the skin, so we don't have to put our trust in poorly regulated supplement companies to not mislabel their products. Only about half the brands came within 10% of their labeled amount. And sunlight may have benefits beyond vitamin D. Like the amazing story about how your body may use the sun's near-infrared rays that penetrate your skin to activate chlorophyll byproducts in your bloodstream to make CoQ10. Well, there's another way. Your body appears to use the sun's rays to maximize the effects of the greens we eat. Within 30 minutes of exposure to the ultraviolet rays in sunlight, you can get a significant drop in blood pressure and improvement in artery function thanks to a burst of nitric oxide-releasing compounds that flow into your bloodstream. You can even measure the nitric oxide gas gassing straight off of your skin. Of course, you actually have to eat your greens or beets in the first place for this to happen, but that combo of greens and sunlight may help explain some of the protection that plant-based eaters experience. Using sun exposure may help those with seasonal effective disorder, as well as improve the mood of wheelchair-bound nursing home residents. I've talked about the benefits of avoiding light at night, but under exposure to daytime sunlight may also affect our melatonin levels, which doesn't just regulate our circadian rhythms, but may also be helpful in the prevention of cancer and other diseases. Earlier men and women getting two hours of outside light during the day appeared to secrete 13% more melatonin at night, though we're not sure what, if any, clinical significance this has. The downsides of sun exposure include increased risk of cataracts, a leading cause of vision loss, though this risk can be minimized by wearing a brimmed hat and sunglasses. Light also ages your skin, as illustrated here. Who can guess what profession this guy was in? He was a truck driver who spent his decades getting more sun on the left side of his face, even through a window. You can see what sun can do. The effects of sunlight on the skin are profound, accounting for up to 90% of visible skin aging, wrinkles, thickening, loss of elasticity, things like sun exposure and smoking, can make you look 11 years older. Cosmetic surgery can make you look 8 years younger, but a healthy lifestyle may work even better. The reason doctors preach sun protection, though, is not for youthful facial looks, but because of skin cancer. Medical authorities from the World Health Organization, American Cancer Society and the Surgeon General, warn about excess sun exposure and for good reason, given the millions of skin cancers and thousands of deaths diagnosed every year in the US alone. The UV rays in sunlight are considered the so-called complete carcinogen, meaning they can not only initiate cancer, but promote its progression and spread. Melanoma is the scariest, which makes the rising incidents among young women particularly alarming. This increase has been blamed on the increased usage of tanning salons. Tanning beds and UV rays in general are considered Class 1 carcinogens, like processed meat, accounting for as many as three quarters of melanoma cases among young people. Six times the risk of melanoma for those who visited tanning salons ten or more times before the age of 30. The tanning industry is big business, bringing in billions. There may be more tanning salons than there are Starbucks, and they use those dollars, like the tobacco industry, to downplay the risks of their products. Now laws are being passed to regulate tanning salons, including complete prohibitions, like in the country of Brazil, to age restrictions for minors. But unlike tobacco, tanning isn't addictive, or is it? There are people who tan compulsively and report a so-called tanners high. Describing tanny behavior like a substance abuse disorder seems on-face a little silly until you stick people in a brain scanner and can show the same kind of reward pathways light up in the brain, thanks to endorphins released by your skin when you're exposed to UV rays, such that you can even induce withdrawal-like symptoms giving tanners opiate-blocking drugs. So potentially addictive, but dangerous, Harvard researchers suggesting we should view recreational tanning and heroin abuse as engaging in the same biological pathways. But there's a reason sun exposure feels good. That's a good thing, evolutionarily, because sunlight is the primary natural source of vitamin D. So throughout evolution, right, it's more important in terms of passing along your genes to not die of rickets in childhood. Forget skin cancer in your old age. Unlike natural sunlight, tanning bed lights emit mostly UVA, which is the worst of both worlds, cancer risk with little or no vitamin D production. With a small amount of UVB, many do admit may be enough to raise vitamin D levels. If only there was a way to raise vitamin D levels without risking cancer, there is vitamin D supplements.