Vitamin D activities and metabolic bone disease.

Abstract

Vitamin D activity requires an adequate vitamin D status as indicated by the serum level of 25-hydroxyvitamin D and appropriate expression of genes coding for vitamin D receptor and 25-hydroxyvitamin D 1α-hydroxylase, the enzyme which converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. Vitamin D deficiency contributes to the aetiology of osteomalacia and osteoporosis. The key element of osteomalacia, or rickets in children, is a delay in mineralization. It can be resolved by normalisation of plasma calcium and phosphate homeostasis independently of vitamin D activity. The well characterised endocrine pathway of vitamin D metabolism generates plasma 1,25-dihydroxyvitamin D and these endocrine activities are solely responsible for vitamin D regulating plasma calcium and phosphate homeostasis and protection against osteomalacia. In contrast, a large body of clinical data indicate that an adequate serum 25-hydroxyvitamin D level improves bone mineral density protecting against osteoporosis and reducing fracture risk. Recent research demonstrates that the three major bone cell types have the capability to metabolise 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D to activate the vitamin D receptor and modulate gene expression. Dietary calcium intake interacts with vitamin D metabolism at both the renal and bone tissue levels to direct either a catabolic action on bone through the endocrine system when calcium intake is inadequate or an anabolic action through a bone autocrine or paracrine system when calcium intake is sufficient.

• Authors: Jackson W Ryan, Paul H Anderson, Andrew G Turner, Howard A Morris
• Journal: Clinica chimica acta; international journal of clinical chemistry (Clin Chim Acta) Vol. 425 Pg. 148-52 (Oct 21 2013) ISSN: 1873-3492 [Electronic] Netherlands
• PMID: 23911750 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Review)
• Copyright: © 2013.

Chemical References

• Phosphates
• Receptors, Calcitriol
• Vitamin D
• 1,25-dihydroxyvitamin D
• 25-hydroxyvitamin D
• 25-Hydroxyvitamin D3 1-alpha-Hydroxylase
• Calcium

Topics

• 25-Hydroxyvitamin D3 1-alpha-Hydroxylase (genetics, metabolism)
• Bone Density
• Bone and Bones (metabolism, pathology)
• Calcification, Physiologic
• Calcium (metabolism)
• Child
• Gene Expression Regulation
• Humans
• Osteomalacia (etiology, metabolism, pathology)
• Osteoporosis (etiology, metabolism, pathology)
• Phosphates (metabolism)
• Receptors, Calcitriol (genetics, metabolism)
• Vitamin D (analogs & derivatives, metabolism)
• Vitamin D Deficiency (complications, metabolism, pathology)