News reports frequently mention vitamin D, but often fail to note that it comes in two distinct forms: D3, also known as cholecalciferol, and D2, also known as ergocalciferol. These two forms come from different sources and may have different bioavailability and biological activity, although the jury is still out on whether those differences truly exist.
Vitamin D
Vitamin D participates in bone growth and remodeling in the body. Working together with calcium, this vitamin protects bones from osteoporosis. Vitamin D also acts in the immune system, reduces inflammation, modulates gene expression and helps control cell growth. Deficiencies in childhood can lead to the disorder rickets, which causes soft bones and skeletal deformities. In adults, the disorder osteomalacia, a weakening of the bones.
Sources
The skin can produce vitamin D3 when exposed to direct sunlight, but people who often remain indoors or who live in northern climates often cannot produce enough. Vitamin D3 synthesis occurs in other animals as well, so food sources such as fish, eggs and cod liver oil contain it. Laboratory-synthesized vitamin D3 is also available. Plants produce vitamin D2, which can then be isolated and sold in supplement form. Another source of vitamin D2 is a form of mushroom that produces the nutrient upon exposure to UV light. Fortified foods, such as milk and juice, may contain either D2 or D3. Prescription shots of vitamin D, given to treat a severe deficiency, usually consist of vitamin D2.
Bioactivity
The evidence for the bioactivity of the two different forms of vitamin D has been mixed, so controversy exists over whether they are similarly effective. However, a study in the December 2010 issue of the "Journal of Clinical Endocrinology & Metabolism" found that vitamin D3 is 87 percent more effective at raising blood serum levels of vitamin D than the D2 form. The body also stores vitamin D3 more effectively, according to the study. This research directly contradicts some previous research, such as a March 2008 paper in the same journal that found Vitamins D2 and D3 equally effective at raising blood vitamin D levels.
Considerations
Since vitamin D3 only comes from animal sources, vegetarians may prefer vitamin D2 as a supplement or in fortified foods. Because of the potential differences between vitamin D2 and D3 absorption, vitamin D2 is often given at a higher dose than D3. The recommended dose of vitamin D in either form is 600 IU for everyone between the ages of 1 and 70.
References
- NIH Office of Dietary Supplements: Vitamin D
- MayoClinic.com: Vitamin D
- PubMed.gov: Vitamin D3 Is More Potent Than Vitamin D2 in Humans; R. P. Heaney, et al.; Dec 2010
- PubMed.gov: Vitamin D2 is As Effective as Vitamin D3 in Maintaining Circulating Concentrations of 25-hydroxyvitamin D; M.F. Holick, et al.; Mar 2008.
- The Vegetarian Resource Group: FAQs About Vitamin D
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