A large study may have raised more questions than it answered about whether calcium and vitamin D supplements reduce the risk of hip fracture.
At first glance, the widely used preventive therapy slightly improved hip bone density, but didn't make hip fracture less likely, said investigators with the multicenter Women's Health Initiative.
But a closer look showed a 29 percent decrease in hip fractures in the subset of women who were most diligent about taking the supplements. The findings appear today in the New England Journal of Medicine.
"It's really important from a public health perspective because it's a low-cost means of preventing hip fracture," said WHI investigator Jane Cauley
, an epidemiologist at the University of Pittsburgh Graduate School of Public Health
More than 36,000 postmenopausal women ages 50 to 79 participated in the study. They were randomly assigned to daily take either 1000 milligrams of calcium carbonate with 400 international units of vitamin D or a placebo. They were monitored for an average of seven years.
The supplement group had 14 hip fractures per 10,000 women and the placebo group had 16 per 10,000 women.
That might suggest the supplements didn't provide a dramatic benefit, but Dr. Cauley said the results may have been diluted by including women who didn't closely follow the regimen.
When investigators looked at the women who took 80 percent or more of the recommended dose, they found a 29 percent reduction in hip fractures, a substantial effect. "Although the trial was well conducted, the results of the current study leave many questions unanswered," said Dr. Joel S. Finklestein, of Massachusetts General Hospital, in a journal commentary.
The trial's design may have made it more difficult to detect a treatment benefit, he said. The participants did not have an especially high risk of developing fractures, so it's possible the supplements would be more helpful in women who already have osteoporosis.
Also, almost two-thirds of the women in the placebo group ingested 800 mg of calcium daily and about 40 percent received at least 400 IU of vitamin D daily through their typical diet and supplement use. And, the treatment dose of vitamin D probably should have been around 700 IU to see an effect, Dr. Finkelstein added.
He noted that more than half of the treatment and placebo groups were getting hormone-replacement therapy, which has been shown to reduce fracture risk.
Calcium and vitamin D supplementation did not appear to reduce the risk of arm, wrist or vertebral fractures.
Still, women should strive to meet recommendations through diet and supplements, Dr. Finkelstein said. Women 51 or older need 1,200 mg of calcium daily. "Calcium with vitamin D supplementation is akin to the ante for a poker game: it is where everyone starts," he said. But, he added, those at greater risk for hip fracture will likely need other treatments, too.
The study also found a 17 percent increased risk of kidney stones among women taking the supplements.
"People who have a history of kidney stones perhaps need to discuss with their doctor whether or not they should take the calcium supplements," Dr. Cauley said.
By: Anita Srikameswaran | Pittsburgh Post Gazette
February 16, 2006