Vitamin D May Not Help Black Women's Bones

Differences in absorption and metabolism argue against supplements, study finds

MONDAY, July 25, 2005 (HealthDayNews) -- There's been ongoing controversy about just how much vitamin D women need, along with calcium, to prevent bone loss as they age.

Now a new study adds another twist to the debate with this finding: Black women may not need as much vitamin D as white women do.

Calcium supplements are important for reducing bone loss in older women, and vitamin D -- which the body makes naturally through exposure to sunlight -- plays a vital role in helping the body absorb that calcium. Supplements can also be used to raise vitamin D levels.

However, differences between black and white women in their ability to absorb vitamin D and metabolize calcium may mean black women don't need to have their levels of the vitamin raised as much as white women do, researchers say.

Black women synthesize less vitamin D through skin exposure to sun, meaning that "African-American women have lower vitamin D levels than white women," explained lead researcher Dr. John F. Aloia, from Winthrop University Hospital in Mineola, N.Y.

Interestingly, the study also found that simply taking vitamin D as a supplement did nothing to improve bone health in black women.

The report appears in the July 25 issue of the Archives of Internal Medicine.

According to Aloia, there's been a lot of data suggesting that women's daily vitamin D intake should be higher than what is taken normally.

In the study, Aloia's team randomly assigned 208 healthy black women, aged 50 to 75 years, to receive either 20 micrograms a day of vitamin D3 or a placebo. In addition, all the women received calcium supplements. After two years, the researchers increased the dose of vitamin D3 to 50 micrograms per day. All of the women underwent bone mineral density scans every six months during the three years of the study, to check for changes in bone health.

"There was really no difference in bone loss with vitamin D supplementation," Aloia said. "Raising vitamin D levels did not show an advantage in terms of bone health." However, calcium supplementation did cause an increase in bone mineral density in both groups, he said.

The question of whether vitamin D intake needs to be increased among black women has been controversial, Aloia noted. "Our conclusion is that it does not need to be increased," he said. "Calcium metabolism is more efficient in black women than in white women, so there may be a benefit in vitamin D supplementation in white women, [but] black women may not need as high vitamin D levels to maintain their bone density."

One expert believes the study data is flawed, however. "The major problem with the study is that the women were vitamin D-deficient, and the researchers never corrected their vitamn D-deficiency," said vitamin D expert Dr. Michael F. Holick, director of the Vitamin D Laboratory at Boston University.

Holick believes that women need at least 1,000 international units or greater of vitamin D3 a day to maximize calcium absorption. "These researchers never reached these levels," he said. "All they have done is to partially correct the vitamin D deficiency."

Because the amount of vitamin D obtained through the average American diet is insignificant, Holick still recommends that women take a supplement.

Another expert said Aloia's study raises important doubts about the utility of vitamin D supplementation, however.

"Clinically, I would still suggest that all postmenopausal women use vitamin D and calcium supplementation as part of a general wellness program," said Dr. Stephen Honig, the director of the Osteoporosis Center at the Hospital for Joint Diseases in New York City. "However, it is important to note that there is no evidence at this time that such a recommendation for healthy community-dwelling people will reduce the incidence of fragility fracture, which is what physicians are trying to do."

More information

The National Institutes of Health can tell you more about vitamin D supplements.

SOURCES: John F. Aloia, M.D., Winthrop University Hospital, Mineola, N.Y.; Michael F. Holick, M.D., Ph.D, director, Vitamin D Laboratory, Boston University, Boston; Stephen Honig, M.D., director, Osteoporosis Center, Hospital for Joint Diseases, New York City; July 25, 2005, Archives of Internal Medicine
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