Vitamin D2 vs. D3
Which is better, vitamin D2 or D3? I have several updates concerning vitamin D, including 12/11/2004, 5/23/2003, and 5/29/2003. Read the abstract by Holick MF for a quick summary of the metabolism of vitamin D to help you understand this important vitamin. In the U.S. there is only one form of vitamin D that is available over the counter, vitamin D2, which is generally thought to be equal in potency to vitamin D3. However, a recent study by Armas LA and others, J Clinc Endocrinol Metab. 2004 Nov;89(11):5387-91. PMID: 15531486, has found that vitamin D3 is much more potent. The 20 healthy male volunteers in this study received only a single dose of 50,000 IU of vitamin D2 or D3. The authors found similar serum concentrations of serum 25OHD (the next active form of vitamin D produced in the liver from vitamin D3) after three days. The vitamin D2 level fell rapidly and reached baseline in 14 days. The vitamin D3, however, didn't peak until day 14. Statistical calculations showed vitamin D3 was at least three times more potent that vitamin D2 in this study. Editor's comments: The first question that comes to mind is regarding my vitamin D2 dosage of 800 IU taken orally per day. Because I'm taking it daily, and the 50,000 IU doses of either vitamin D2 or D3 were equal over the first three days, does that mean that daily oral doses of vitamin D2 would also be equal to daily oral doses of vitamin D3? The other question revolves around the alternatives to vitamin D2 for people living in this country. Essentially, as far as I know, there is only one: Sunlight. If you are concerned that you aren't getting adequate vitamin D from your supplement, it is recommended you get 10-15 minutes of sunlight to your arms, legs, hands, or face at least two or three times a week. Of course, it is probably wise to have your serum 25-hydroxyvitamin D levels tested occasionally to verify that whatever approach you are taking is adequate for you. In case you are receiving the once-monthly 50,000 IU of vitamin D2, it is highly recommended that you monitor your 25-hydroxyvitamin D levels very closely. The results of this study suggest you probably aren't getting adequate amounts of vitamin D2 to promote proper absorption of calcium from the foods you eat.