Vitamin D3 Vs. Vitamin D

Many people know they need vitamin D for good health. Vitamin D is critical for bone health, but it has also been shown to have a protective effect against certain diseases, including colon and prostate cancer and autoimmune diseases. But many people are confused by which type of vitamin D to take and what the differences are between them: D2 or D3?

Vitamin D3

The Vitamin D Council states that the current system of naming vitamin D is confusing and often misleading. The naturally occurring form of vitamin D is known as cholecalciferol, or vitamin D3. When you see a reference to Vitamin D without any number attached, the reference is usually to vitamin D3. This form of vitamin D is a fat soluble vitamin that is available in very few foods, is often added to other foods, or is taken as a supplement. It is naturally produced when ultraviolet rays from sunlight strike your bare skin. It is artificially produced for supplements by radiating lanolin. Vitamin D3 is inactive biologically and needs to be changed, or hydroxylated, twice in the body to become active.

Hydroxyvitamin D

The first change occurs in the liver, which converts vitamin D3 to 25 hydroxyvitamin D, also called calcidiol. This form, like vitamin D3, is inactive in the body. The second change occurs in the kidney, which converts calcidiol to 1,25 hydroxyvitamin D, called calcitriol. Calcitriol, a potent steroid hormone, is the active form of vitamin D in the body.

Vitamin D2

Vitamin D2 is known as ergocalciferol. It is not normally found in the body and has no purpose in humans. Ergocalciferol is obtained from radiating yeast and is often the vitamin D that is in supplements. Vitamin D2 can be converted into calcitriol, but vitamin D3 is more than 3 times as effective as vitamin D2 in the body. Consequently, many supplements are trending away from using vitamin D2.

Effects

Vitamin D has a number of important functions, and more are being discovered. The best studied function of vitamin D is preserving bone health. Vitamin D promotes calcium absorption in the gut and helps maintain adequate blood levels of calcium and phosphorus, all of which are important for strong bones. Low levels of vitamin D cause rickets, osteopenia, osteoporosis and frequent fractures. According to a 2007 review article by Boston University professor Dr. Michael Holick in the "New England Journal of Medicine," vitamin D deficiency also has been shown to increase the incidence of many diseases, including prostate, breast and colon cancer, autoimmune diseases such as multiple sclerosis and diabetes, hypertension and cardiovascular disease, psoriasis, depression and schizophrenia. Low levels of vitamin D also have been associated with a higher mortality rate.

At-risk Groups

It is estimated that up to 32 percent of otherwise healthy people may have undiagnosed vitamin D deficiency or very low levels of vitamin D. Some groups are at high risk of vitamin D deficiency: the elderly, babies who are exclusively breastfed, patients with kidney or liver failure, people with malabsorption problems like cystic fibrosis and people who don't get much sun exposure to their skin. When measuring vitamin D levels, the best test is the level of 25 hydroxyvitamin D, often written as 25-OH vitamin D. Levels of 25 hydroxyvitamin D should be higher than 30 ng/ml to prevent vitamin D deficiency.

Supplements

There are a variety of supplements on the market. Make sure that the vitamin D is D3, or cholecalciferol. If you fall into one of the risk groups mentioned above, you should consult your doctor to consider testing your vitamin D level or getting prescription forms of vitamin D. The resource section lists the November 2010 recommendations from the National Institutes of Health for vitamin D and calcium intake for different groups of people. These recommendations suggest higher daily intake of vitamin D than previous recommendations.