The use of vitamin D supplements does not appear to slow bone loss in healthy, postmenopausal black women, according to the results of a new study.

“I was surprised by the results,” lead author Dr. John F. Aloia, from Winthrop University Hospital in Mineola, New York, told Reuters Health. “Because black women synthesize less vitamin D with sun exposure than white women, they have lower levels. Therefore, I thought that by increasing these levels, supplementation might help reduce bone loss - but it didn’t.”

Aloia noted that previous studies looking at the effects of vitamin D supplementation in white women have yielding conflicting results.

He added that his group decided to focus on black women because their low vitamin D levels make them a “vulnerable population.”

The study, published in the Archives of Internal Medicine, involved 208 healthy postmenopausal black women who were randomly assigned to receive vitamin D supplements or a placebo for three years. None of the women were receiving hormone replacement therapy.

The vitamin D dose was 800 IU for the first two years and 2000 IU for the last year. All of the subjects were also given calcium supplements to achieve a daily intake of 1200 to 1500 mg per day.

Bone mineral density did not differ significantly between the two groups throughout the entire study period, the researchers note. Furthermore, blood levels of vitamin D did not correlate with bone loss rates.

Both groups of women experienced an increase in bone mineral density in the total body, hip, and radius at one year. In the three-year analysis, however, bone mineral density fell at these sites by up to 0.55 percent per year. A slight increase in bone mineral density of the lower spine was seen in both groups.

Exactly why no benefit for supplementation was seen is unclear, Aloia noted. However, it may relate to the fact that calcium metabolism is more efficient in black women than in white women, so there might not be as much room for vitamin D supplementation to enhance the process, he explained.

Aloia added that his group is now studying the differences between white and blacks in how vitamin D is processed in the body. “We hope to conduct a study similar to the current one, giving the (2000 IU) dose of vitamin D3 to white women.”

SOURCE: Archives of Internal Medicine, July 25, 2005.