RESUMO
Vitamin D and its metabolites are crucial to the overall health and well-being of humans and animals, having important functions in calcium homeostasis and bone metabolism. Exposure of the skin to sunlight may provide adequate levels of vitamin D; however, there are numerous reports of vitamin D insufficiency or deficiency. 25-hydroxyvitamin D (calcidiol, 25(OH)D) is regarded as the best measurement of overall vitamin D status. 1,25-dihydroxyvitamin D (calcitriol, 1,25(OH)2D) is the most biologically active vitamin D metabolite. 25(OH)D has higher affinity for vitamin D binding protein (VDBP) than 1,25-dihydroxyvitamin D; whereas, 1,25-dihydroxyvitamin D has higher affinity for the vitamin D receptor (VDR) than 25-hydroxyvitamin D. HPLC and immunoassays allow the determination of vitamin D status, as measured by 25(OH)D, and 1,25(OH)2D. Recently it has been shown that the vitamin D requirements have been underestimated and that vitamin D2 is much less potent than vitamin D3. Future studies will determine the amount of vitamin D3 necessary for optimal health and well-being.
