Best Form of Vitamin D
Written By: Researchers at the University of California, San Diego
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Published - Apr 6, 2010
Q: I hear that vitamin D has been found to help prevent cancer and that "vitamin D3" is recommended. The label on my multivitamin supplement says vitamin D, not D3. Are they the same thing? I'm stumped.
A: This news is based on a recent review by researchers at the University of California, San Diego.
Vitamin D is commonly called the "sunshine" vitamin. Along with calcium, it helps prevent osteoporosis.
The news releases I saw, including those from the university itself, mentioned vitamin D3 without explanation. We'll clarify the puzzlement shortly.
Researchers noted that vitamin D deficiency is widespread, and said their findings suggest that boosting daily intake of vitamin D3 to 1000 IU (increased almost every year since - in 2010 to 10,000 IU daily) would substantially cut the risk of cancers of the colon, breast, ovaries and prostate.
The findings are based on an analysis of dozens of vitamin D observational studies.
It should be said that observational studies can detect associations but don't prove cause and effect. In this way, they fall short of double-blind placebo trials, a limitation the researchers readily admitted.
Even so, they reasoned, 1000 IU of vitamin D daily is considered safe, so increasing intake to this level would be good insurance. (The recommended safe daily intake level is 2000 to 10000 IU.)
Now to unravel the puzzlement. There are two relevant forms of vitamin D: D2 and D3.
D2 (ergocalciferol) is present in plant sources. D2 is our primary dietary source of vitamin D and is the form used in vitamin D-fortified milk and cereal products.
D3 (cholecalciferol) is the form our body synthesizes when skin is exposed to sunlight.
Both forms are converted to active vitamin D by the body. However, studies have determined that vitamin D3 is about three times more potent than vitamin D2 in the conversion process.This is likely the reason researchers recommend the D3 form of vitamin D.
In most cases, brief periods of unprotected (without sunscreen) sun exposure to face and arms can meet the body's vitamin D needs.
But researchers think that most people, particularly those with darker skin or who live in northern states, can more easily meet the target level of 2000-10000 IU through diet and vitamin D supplements.
Vitamin D is available in both multivitamin and vitamin D-only supplements.
Standard multivitamin supplements supply 800-2000 IU of vitamin D, considered a low-end amount.
The catch is, the vitamin D may be either D2 or D3, and 2000 IU of D2 is far less potent than the same amount of D3.
As you pointed out, the Supplement Facts label typically just says "Vitamin D." So how to tell which form you're getting?
You'll have to peruse the "Ingredients" section of the label, which is not alphabetized. With some products, this is an ordeal that cries for a magnifying lens.
If the product provides D2, you'll see either "vitamin D2" or "ergocalciferol."
If D3, you'll see either "vitamin D3" or "cholecalciferol."
My hunch is that supplement manufacturers now using D2 may feel pressured to switch to D3.