Vitamin D

Vitamin D is a fat-soluble vitamin that exists in two physiologically relevant forms, ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Ergocalciferol is synthesized by plants and mushrooms, while cholecalciferol is synthesized by humans in the skin when it is exposed to ultraviolet-B (UVB) rays from sunlight. Some foods may also be fortified with vitamin D, such as milk and breakfast cereals. The current average daily intakes of vitamin D for Americans are well below suggested adequate intakes1, and much of the world’s population is deficient in this important vitamin 2.

The main function of vitamin D is to regulate serum calcium and phosphorus concentrations within the normal range by enhancing the efficiency of the small intestine to absorb these minerals. By influencing the absorption of calcium, vitamin D helps to form and maintain strong bones and teeth 3,4.

Vitamin D supplementation helps prevent falls and maintain physical performance in the elderly4,5. Adequate vitamin D intake may also be important for maintaining immune health6,7, nervous system health8, may help improve mood during the winter months9,10 and improve overall quality of life11.

Vitamin D is generally well tolerated at recommended doses. The U.S. Food and Drug Administration (FDA) has established a Reference Daily Intake (RDI) of 400 international units (IUs) vitamin D for adults and children 4 or more years of age. RDIs are a set of dietary references for essential vitamins and minerals that are considered amounts sufficient to meet the daily requirements of healthy individuals. RDIs serve as the basis for calculating the percent daily value (% DV) amounts found on dietary supplement and food labels.

According to the Endocrine Society’s Vitamin D Clinical Practice Guidelines, individuals who are at risk for vitamin D deficiencies should ask their physician to have their blood tested for the vitamin D metabolite [25(OH)D]. For individuals with blood 25(OH)D levels <75 nmol/L, higher amounts of vitamin D intake are suitable: children ages 1–18 may need 600–1,000 IU daily,adults >18 age may need 1,500–2,000 IU vitamin D daily12.

 Many Americans Would Benefit from Intake of Supplemental Vitamin D Higher than Current RDAs


  1. USDA Dietary Guidelines Advisory Committee. Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2010. 2010.
  2. Mithal A, Wahl DA, Bonjour JP et al. Global vitamin D status and determinants of hypovitaminosis D. Osteoporos.Int 2009;20:1807-20.
  3. Palacios C. The role of nutrients in bone health, from A to Z. Crit Rev Food Sci Nutr 2006;46:621-8..
  4. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. 2010.
  5. Annweiler C, Montero-Odasso M, Schott AM, Berrut G, Fantino B, Beauchet O. Fall prevention and vitamin D in the elderly: an overview of the key role of the non-bone effects. J Neuroeng.Rehabil. 2010;7:50.
  6. van Etten E, Mathieu C. Immunoregulation by 1,25-dihydroxyvitamin D3: basic concepts. J Steroid Biochem Mol Biol 2005;97:93-101.
  7. Maggini S, Wintergerst ES, Beveridge S, Hornig DH. Selected vitamins and trace elements support immune function by strengthening epithelial barriers and cellular and humoral immune responses. Br J Nutr 2007;98 Suppl 1:S29-S35. .
  8. McCann JC, Ames BN. Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction? FASEB J 2008;22:982-1001.
  9. Bertone-Johnson ER. Vitamin D and the occurrence of depression: causal association or circumstantial evidence? Nutr Rev 2009;67:481-92. 10. .
  10. Lansdowne AT, Provost SC. Vitamin D3 enhances mood in healthy subjects during winter. Psychopharmacology (Berl) 1998;135:319-23. .
  11. Norman AW, Bouillon R. Vitamin D nutritional policy needs a vision for the future. Exp Biol Med (Maywood.) 2010;235:1034-45.
  12. Holick MF, Binkley NC, Bischoff-Ferrari HA et al. Evaluation, treatment, and prevention of vitamin d deficiency: an endocrine society clinical practice guideline. J Clin Endocrinol Metab 2011;96:1911-30.