Health effects of sunlight exposure

Exposing skin to the ultraviolet radiation in sunlight has both positive and negative health effects. On the positive side, exposure allows for the synthesis of vitamin D₃. Vitamin D has been suggested as having a wide range of positive health effects, which include strengthening bones^[1] and possibly inhibiting the growth of some cancers.^[2][3] A dietary supplement can also supply vitamin D,^[4] but there are also benefits to exposure not obtainable through Vitamin D supplementation. Long-term sun exposure is associated with reduced all-cause mortality and reduced mortality risk from cardiovascular disease (CVD), some forms of cancer, and non-CVD/noncancer related disease, with indications in these studies that Vitamin D is not the mediator.^[5][6][7] Supplementation offers limited bioavailability and no synthesis of subdermal nitric oxide.^[8][9] UV exposure also has positive effects for endorphin levels, and possibly for protection against multiple sclerosis. Abundant visible light to the eyes gives health benefits through its association with the timing of melatonin synthesis, maintenance of normal and robust circadian rhythms, and reduced risk of seasonal affective disorder.^[10]

On the negative side, UV is a mutagen and carcinogen for skin.^[11][12] Acute exposure may lead to a painful sunburn, which can increase the chances of developing serious skin problems later in life.^[13] Long-term sunlight exposure is known to be associated with the development of some types of skin cancer, skin aging, immune suppression, eye diseases such as cataracts.^[14][15]

Since UV rays, and therefore sunlight and sunlamps, have both health benefits and risks, a number of public health organizations state that there needs to be a balance between the risks of having too much sunlight or too little.^[16] There is a general consensus that sunburn should always be avoided.