What Is Vitamin D-2?

Vitamin D-2, also known as ergocalciferol, is one of two forms of vitamin D useful as a dietary source of this vitamin. Like the other form -- vitamin D-3 -- vitamin D-2 must be converted into an active form before the body can use it. The form 25-hydroxyvitamin D, also known as calcidiol, is created from vitamin D-2 or D-3 by the liver and can be measured in the blood to determine whether there is a deficiency.

Importance

All forms of vitamin D, including vitamin D-2, help with the absorption of calcium by the body. Vitamin D also plays a role in blood pressure regulation and immune system maintenance. Insufficient levels of vitamin D can lead to bone deformities. Vitamin D-2, taken as a supplement or acquired through food sources, may help prevent a wide range of health problems, including osteoporosis, cardiovascular disease and certain types of cancer.

Sources

Vitamin D-2 is the form found in plant sources of vitamin D. Plants and yeasts create vitamin D-2 from a molecule called ergosterol when exposed to ultraviolet light. Vitamin D-2 is sometimes added to fortified foods and beverages, such as orange juice. Mushrooms grown under ultraviolet light may also be high in vitamin D-2. Some supplements also contain vitamin D-2, especially high-dose vitamin D supplements used for treating deficiencies.

Alternatives

The other important dietary form of vitamin D is vitamin D-3. Vitamin D-3 is synthesized by animals and can be found in animal products such as milk. Vitamin D-3 is also the form produced by the skin during sun exposure. Some foods are fortified with vitamin D-3 instead of vitamin D-2, and some supplements use this form as well.

Concerns

A 2006 study in the "American Journal of Clinical Nutrition" found that vitamin D-2 is not as biologically effective as vitamin D-3 when taken in supplement form. Ingestion of vitamin D-3 was better at raising the amount of 25-hydroxyvitamin D in the bloodstream than vitamin D-2. Vitamin D-2 also did not bind to necessary proteins in the body as efficiently as vitamin D-3. Also, the shelf life of vitamin D-2 is shorter than vitamin D-3 in commercial supplements.

Health Implications

Because it may be as much as three times more effective than vitamin D-2, vitamin D-3 is becoming the preferred form of this nutrient. However, according to the National Institutes of Health Office of Dietary Supplements, either form is effective for raising blood serum levels of vitamin D enough to treat deficiencies. Vitamin D-2 has been used in the past to treat rickets, a condition caused by severe vitamin D deficiency.