, circulating vitamin D concentrations were determined in two lightly pigmented Caucasian and three heavily pigmented Negro volunteers after exposure to a single standard dose of ultraviolet radiation (UVR). Exposure of Caucasian subjects to 1 minimal erythemal dose of UVR greatly increased serum vitamin-D concentrations by up to 60-fold 24-48 h after exposure, whereas this dose did not significantly change serum vitamin-D concentrations in Negro subjects.
Exposure of Caucasian subjects to 1 minimal erythemal dose of UVR greatly increased serum vitamin-D concentrations by up to 60-fold 24-48 h after exposure, whereas this dose did not significantly change serum vitamin-D concentrations in Negro subjects. Re-exposure of one Negro subject to a dose of UVR six times larger than the standard dose increased circulating vitamin D to concentrations similar to those recorded in Caucasian subjects after exposure to the lower dose.
Only a few foods, such as the flesh of fatty fish, contain significant amounts of vitamin D, and fish does not contain enough vitamin D to achieve optimal Vitamin D status without sunlight or supplements.
Dietary recommendations typically assume that all of a person's vitamin D is taken by mouth, as sun exposure in the population is variable and recommendations about the amount of sun exposure that is safe are uncertain in view of the skin cancer risk.
A diet with insufficient vitamin D in conjunction with inadequate sun exposure causes vitamin D deficiency.
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Severe vitamin D deficiency in children causes rickets, a softening and weakening of bones, which is a rare disease in the developed world.
Instead it could be considered a hormone, with activation of the vitamin D pro-hormone resulting in the active form, calcitriol, which then produces effects via a nuclear receptor in multiple locations.
Cholecalciferol is converted in the liver to calcifediol (25-hydroxycholecalciferol); ergocalciferol is converted to 25-hydroxyergocalciferol.
Calcitriol also has other effects, including some on cell growth, neuromuscular and immune functions, and reduction of inflammation.
Vitamin D has a significant role in calcium homeostasis and metabolism.