16. Skin
Many people like spending time in the sun in order to get a tan, but they should be aware that this is not good for them. Being in the sun causes damage due to radiation and a tan is actually sign of that damage.
That said though, vitamin D is good for the skin. In fact, light exposure is one of the best known treatments for psoriasis – the condition that causes the abnormal growth of skin cells resulting in flaky, unappealing plaques.
This is likely to do with the power of vitamin D over the immune system (psoriasis is an autoimmune disease).