The most important thing about sun exposure is that it helps to replenish and synthesize vitamin D. Vitamin D is the result of ultraviolet rays from the sun hitting the skin, which uses cholesterol as a raw material to synthesize vitamin D, mainly vitamin D3, of course. vitamin D3 doesn’t work right away, and a part of it is stored in the fats; the other part of it enters the bloodstream and hangs up two hydroxyls in the liver and in the kidneys in the first place, which is not a real gun of course but a chemical group that becomes active. The chemical group becomes the active vitamin D, which helps the kidneys to absorb calcium and acts in the intestines to help absorb calcium from food. The most important role of vitamin D is closely related to bone health, but of course it’s now being discovered that it has non-classical roles, and that vitamin D is critical to cardiovascular health, tumor reduction, and immune function. There is very little vitamin D in food, mushrooms, fungus or fish from the deep sea contain very small amounts of vitamin D. If you are deficient in vitamin D, the best thing you can do is to get some sunlight. Be in the sun between 10 a.m. and 2 p.m., as well as every day for 30 minutes at a time to ensure a source of vitamin D.