Vitamin D in health and disease

Vitamin D is the precursor of the steroid hormones 1,25-dihydroxy-vitamin D (1,25(OH)2D). Most of the biological effects of 1,25(OH)2D derive from its interaction with vitamin D receptor (VDR), an intracellular transcription receptor. VDR regulates genes that influence bone mineral homeostasis, immunomodulation, insulin secretion, cell cycle and the detoxification of exogenous and endogenous compounds. The most investigated function of 1,25(OH)2D is the regulation of calcium and phosphate homeostasis and, in turn, the bone turnover rate in skeletal tissue. However, recently also the extra-osseous activity of 1.25 (OH) 2D has received growing attention. Nevertheless, the lack of the definition of optimal vitamin D status and optimal vitamin D dosing regimens limits the knowledge derived from available studies and highlight the need of future well-designed studies on these topics.