Modern views of vitamin D
DeLuca, H.F.
Journal of the Medical Society of New Jersey 78(9): 611-613
1981
ISSN/ISBN: 0025-7524 PMID: 6943358 Document Number: 175381
Vitamin D3 is either synthesized in the skin in response to ultraviolet light or absorbed from dietary sources in the small intestine; 7-dehydrocholesterol is converted to previtamin D3, which slowly equilibrates to vitamin D3. The metabolic activation take place primarily in the liver, resulting in 25-hydroxyvitamin D3 (calcidiol); further activation occurs in the proximal tubule of the kidney in non-pregnant animals. The hormonal form of vitamin D3, calcitriol, is transported to various sites where its vitamin D actions are involved with calcium homeostasis. The production of calcitriol is regulated to a large extent by blood calcium level; the system reacts strongly to provide calcium in times of great need, i.e., pregnancy and lactation. Disturbances in the vitamin D system are related to renal osteodystrophy, hypoparathyroidism, rickets, osteoporosis, and other diseases.