ScienceDaily (Jan. 7, 2008) — Researchers from Boston University School of Medicine (BUSM) have found that vitamin D2 is equally as effective as vitamin D3 in maintaining 25-hydroxyvitamin D status.

Researchers studied healthy adults aged 18-84 who received either placebo, 1,000 International Units (IU) of vitamin D3, 1,000 IU of vitamin D2, or 500 IU of vitamin D2 plus 500 IU of vitamin D3 daily for three months at the end of winter to establish what effect it had on circulating levels of total 25 (OH)D as well as 25(OH)D2 and 25(OH)D3. Sixty percent of the adults were vitamin D deficient at the start of the study.

Adults who received the placebo capsule daily for three months demonstrated no significant change in their total 25(OH)D levels during the winter and early spring. Adults who ingested 1,000 vitamin D2/d gradually increased their total 25(OH)D levels during the first six weeks. Adults who ingested 1,000 IU of vitamin D3 had a baseline 25(OH)D that was statistically no different from the baselines of either the placebo group or the groups that took 1,000 IU of vitamin D2/d or 500 IU vitamin D2 plus 500 IU vitamin D3/d. The vitamin D3 group increased their serum 25(OH)D levels similar to that of the group that ingested vitamin D2.

The circulating levels of 25-hydroxyvitamin D increased to the same extent in the groups that received 1,000 IU daily as vitamin D2, vitamin D3, or a combination of 500 IU vitamin D2 and 500 IU vitamin D3. The 25-hydroxyvitamin D3 levels did not change in the group that received 1,000 IU vitamin D2 daily. One thousand IU of vitamin D2 or vitamin D3 did not raise 25-hydroxyvitamin D levels in vitamin D deficient subjects above 30 ng/ml.

According to BUSM researchers, vitamin D2 has been the main stay for the prevention and treatment of vitamin D deficiency in children and adults and as little as 100 IU of vitamin D2 was found to be effective in the prevention of rickets. Both vitamin D2 and vitamin D3 form 25-hydroxyvitamin D.

Michael Holick, PhD, MD, director of the General Clinical Research Center and professor of medicine, physiology and biophysics at BUSM and senior author of this study, is an internationally recognized expert in vitamin D and skin research. Most recently, he gave the keynote address to the Indian Endocrine Society in India.

"The maintenance of the serum 25(OH)D3 levels was most likely due to the release of vitamin D3 stored in the body fat since skin synthesis of vitamin D3 does not occur during the winter in Boston," said Holick, who is also director of the Bone Healthcare Clinic and the vitamin D, Skin and Bone Research Laboratory at Boston University Medical Center.

"One thousand IU of vitamin D2 daily was as effective as 1,000 IU of vitamin D3 in maintaining serum 25-hydroxyvitamin D levels and did not negatively influence serum 25-hydroxyvitamin D levels," said Holick. "Therefore, vitamin D2 is equally as effective as vitamin D3 in maintaining 25-hydroxyvitamin D status."

The study appears online in the December 2007 issue of the Journal of Clinical Endocrinology & Metabolism.