Vitamin D control of osteoblast function and bone extracellular matrix mineralization.

Vitamin D is the major regulator of calcium homeostasis and protects the organism from calcium deficiency via effects on the intestine, kidney, parathyroid gland, and bone. Disturbances in the vitamin D endocrine system (e.g., vitamin D-dependent rickets type I and type II), result in profound effects on the mineralization of bone. Recent studies with vitamin D receptor knockout mice also show effects on bone. It is questioned whether vitamin D has a direct effect on bone formation and mineralization. In rickets and particular vitamin D receptor knockout mice, calcium supplementation restores bone mineralization. However, the vitamin D receptor is present in osteoblasts, and vitamin D affects the expression of various genes in osteoblasts. This review focuses on the role of vitamin D in the control of osteoblast function and discusses the current knowledge of the direct effects of vitamin D on mineralization. Moreover, the role of vitamin D metabolism and the mechanism of action of vitamin D and interaction with other hormones and factors are discussed.