6 things you should know about vitamin D
Figuring out all the factors that can affect your vitamin D level is complicated. Your body makes vitamin D when sunlight hits the skin. You can also get the vitamin from food (mainly because it’s been added; few foods are natural sources of vitamin D) or by taking a supplement. The process by which the body makes vitamin D is complex. It starts when the skin absorbs rays in the invisible ultraviolet B (UVB) part of the light spectrum. The liver and the kidneys also participate to make a form of the vitamin that the body can use. A number of factors influence a person’s vitamin D levels. Here are six important ones. Where you live. The further away from the Equator you live, the less vitamin D–producing UVB light reaches the earth’s surface during the winter. Residents of Boston, for example, make little if any of the vitamin from November through February. Short days and clothing that covers legs and arms also limit UVB exposure. Air quality. Carbon particles...