Vitamin D and osteoporosis.

In elderly people with marginal exposure to the sunlight, males showed higher serum 25-hydroxycalciferol than females, whereas in those with ample or poor sunlight exposure, serum 25-hydroxycalciferol was higher or very low, respectively, exhibiting no sex difference in the vitamin D metabolite levels. The male predominance in serum 25-hydroxycalciferol levels seen among some aged population would be explained, at least in part, by the result of animal experiment suggesting the stimulatory effect of testosterone on vitamin D biosynthesis induced by ultaviolet irradiation. Testosterone was, furthermore, shown to have hypocalcemic action, probably through suppression of bone resortopton in vitamin D depleted but not in replete rats. Clinical implication of these two-fold effects of testosterone observed in rats was discussed in relevance to male predominance in serum 25-hydroxycalciferol level and bone mineral content in the aged population.