Vitamin D, bone metabolism and fracture risk.

Insufficient serum levels of 25OH vitamin D (25OHD) is a risk factor for osteoporosis. A new paradigm has emerged with the locally synthesized 1,25(OH)2D within osteoblasts and osteoclasts as the essential pathway for the effects of 25OHD in regulating bone remodeling via direct or indirect activation of the specific receptor VDR. Vitamin D has positive effects on fracture risk but these results have been consistently observed whenever daily doses were above 800 UI/d administered to compliant patients together with adequate calcium supplementation and with an achieved biological target of serum 25OHD levels above 30 ng/mL.