Overview of vitamin D
- Sassan Pazirandeh, MD
Sassan Pazirandeh, MD
- Division of Gastroenterology and Hepatology
- Kaiser Permanente Medical Center
- David L Burns, MD
David L Burns, MD
- Associate Professor of Medicine
- Tufts University School of Medicine
- Section Editors
- Kathleen J Motil, MD, PhD
Kathleen J Motil, MD, PhD
- Section Editor — Pediatric Nutrition
- Professor of Pediatric Nutrition
- Baylor College of Medicine
- Marc K Drezner, MD
Marc K Drezner, MD
- Section Editor — Bone Disease
- Professor of Medicine
- University of Wisconsin Medical School
Vitamin D is a fat-soluble vitamin. Very few foods naturally contain vitamin D (fatty fish livers are the exception), so dermal synthesis is the major natural source of the vitamin. Vitamin D from the diet or dermal synthesis is biologically inactive and requires enzymatic conversion to active metabolites (figure 1). Vitamin D is converted enzymatically in the liver to 25-hydroxyvitamin D (25[OH]D), the major circulating form of vitamin D, and then in the kidney to 1,25-dihydroxyvitamin D, the active form of vitamin D.
Vitamin D and its metabolites have a significant clinical role because of their interrelationship with calcium homeostasis and bone metabolism. Rickets (children) and osteomalacia (children and adults) due to severe vitamin D deficiency are now uncommon except in populations with unusually low sun exposure, lack of vitamin D in fortified foods, and malabsorptive syndromes. Subclinical vitamin D deficiency, as measured by low serum 25(OH)D, is very common. In the National Health and Nutrition Examination Survey (NHANES) 2005 to 2006, 41.6 percent of adult participants (≥20 years) had 25(OH)D levels below 20 ng/mL (50 nmol/L) . This degree of vitamin D deficiency may contribute to the development of osteoporosis and an increased risk of fractures and falls in older adults. Vitamin D may also regulate many other cellular functions.
This topic review provides an overview of vitamin D. Other reviews discuss specific issues related to vitamin D:To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
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