Metabolic and cellular activity of vitamin D.

Most of the effects of vitamin D on calcium and phosphorus homeostasis result from an increase in intestinal absorption of calcium and phosphorus and from bone mobilization. These effects are due to 1,25(OH)2D3, one of the renal vitamin D metabolites. Besides ionic mobilization, vitamin D may exert additional effects on bone which depend on metabolites other than 1,25(OH)2D3. Kidneys, parathyroid glands and muscle are probably target organs for vitamin D. The metabolite(s) responsible for these actions remain unknown.