![]() ![]() As a result, dark-skinned people tend to require more UVB exposure than light-skinned people to generate the same amount of vitamin D. It "competes" for UVB with the substance in the skin that kick-starts the body's vitamin D production. ![]() Melanin is the substance in skin that makes it dark. An Australian study that's often cited showed no difference in vitamin D between adults randomly assigned to use sunscreen one summer and those assigned a placebo cream. But as a practical matter, very few people put on enough sunscreen to block all UVB light, or they use sunscreen irregularly, so sunscreen's effects on vitamin D might not be that important. Theoretically, that means sunscreen use lowers vitamin D levels. Sunscreen prevents sunburn by blocking UVB light. In contrast, ozone absorbs UVB radiation, so pollution-caused holes in the ozone layer could end up enhancing vitamin D levels. Carbon particles in the air from the burning of fossil fuels, wood, and other materials scatter and absorb UVB rays, diminishing vitamin D production. Short days and clothing that covers legs and arms also limit UVB exposure. Residents of Boston, for example, make little if any of the vitamin from November through February. The further away from the Equator you live, the less vitamin D–producing UVB light reaches the earth's surface during the winter. The liver and the kidneys also participate to make a form of the vitamin that the body can use.Ī number of factors influence a person's vitamin D levels. It starts when the skin absorbs rays in the invisible ultraviolet B (UVB) part of the light spectrum. The process by which the body makes vitamin D is complex. 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. Your body makes vitamin D when sunlight hits the skin. Figuring out all the factors that can affect your vitamin D level is complicated.
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