Vitamin D2 is a synthetic D2 form used in food fortification and some dietary supplements and is commonly prescribed to patients with low vitamin D status. Vitamin D2 and D3 were considered equivalent until recently. Vitamin D3 is the natural vitamin D that your skin produces from sunlight exposure. Vitamin D3 is more potent at raising vitamin D blood levels than D2, according to clinical data.
Function
Vitamin D comes in two forms. Ergocalciferol is known as D2 and cholecalciferol is vitamin D3. Vitamin D helps your body absorb calcium. It works with calcium to help maintain strong bones and helps regulate your immune system. Low vitamin D status may increase your risk for thinning bones, depression, high blood pressure and breast and colon cancer, according to the University of Maryland Medical Center.
D2 and D3 Metabolism
Vitamin D2 and D3 are both inactive on their own. Your liver must convert them to 5-hydroxy vitamin D -- an active vitamin D form. This is the physiological form your body uses. Health-care providers measure 5-hydroxy vitamin D blood levels, not D2 or D3, to assess your vitamin D status. The normal 5-hydroxy vitamin D blood levels are 30.0 to 74.0 ng/mL (nanograms per milliliter), according to Medline Plus. Ranges vary depending on the laboratory.
D2 vs. D3 Potency
Vitamin D2 and D3 may not share the same capacity to raise active vitamin D blood levels. Clinical data suggest vitamin D3 is more potent, according a study published in the March 2011 issue of "The Journal of Clinical Endocrinology and Metabolism." The study, conducted by researchers at Creighton University in Omaha, Nebraska, found that vitamin D3 is 87 percent more potent in raising 5-hydroxy vitamin D blood levels. The study concluded that vitamin D3 should be the preferred deficiency treatment, based on these results.
Precautions
Vitamin D3 is available as a dietary supplement. However, you should not use it without consulting your doctor first. All supplements have the capacity to cause side effects and interact with your medications. The recommended daily vitamin D intake is 200 IU if you are an adult under age 50 and 400 IU for those over age 50, according to the University of Maryland Medical Center. Excess vitamin D can cause excess thirst, metallic taste, poor appetite and weight loss. Vitamin D supplements may interfere with calcium blocking medications.
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