Many factors influence the body's production of vitamin D, including age, weight, and air quality. Figuring out all the factors that can affect a person's vitamin D levels is complicated. You can get the vitamin from food and by taking supplements , but vitamin D is also produced by the body in a complex process that starts when rays in the invisible ultraviolet B (UVB) part of the light spectrum are absorbed by the skin. The liver, and then the kidneys, are involved in the steps that eventually result in a bioavailable form of the vitamin that the body can use. A review paper about the many factors influencing a person's vitamin D levels appeared in 2011 in Acta Dermato-Venerologica, a Swedish medical journal. We don't have room to cover every factor discussed, so we selected nine that are interesting, important, or both:
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