The older the woman, the more likely it is that consistent use of calcium and vitamin-D supplements will play a role in reducing her risk for osteoporosis, according to the results of a large national clinical trial conducted as part of the Women's Health Initiative (WHI).
In the final set of results answering the initiative's principal questions about women's health, study leaders say that even the slight benefits demonstrated by the trial involving more than 36,000 participants suggest calcium and vitamin-D supplementation provides an overall public health benefit to postmenopausal women.
The findings from the calcium and vitamin-D supplementation arm of the WHI are published in the Feb. 16 issue of the New England Journal of Medicine. A separate article about these supplements and colorectal cancer prevention is published in the same issue.
"Despite recommendations that women should ensure adequate calcium plus vitamin-D intake for postmenopausal bone health, the role of these supplements on reducing fractures has been conflicting. Now, based on the WHI, we have better data to address these issues," said Rebecca Jackson, lead author of the journal article about supplementation and fractures and Ohio State University Medical Center's principal investigator for the WHI. "The value of a study this large is that it does show, even if only on a small scale, that the intervention can be effective to lower the risk of osteoporosis within two to three years. A physician isn't needed to prescribe these supplements. All this means any supplementation of this kind is potentially beneficial, particularly in women over 60 years old. That's a huge finding."
The calcium-with-vitamin-D trial found a small but significant 1 percent higher hip bone density for women taking calcium combined with vitamin D compared to other women taking placebo. During the trial, 374 women who received supplements broke their hips, with a fracture rate of 14 per 10,000 cases per year, compared to 16 per 10,000 fractures per year in the placebo group - a 12 percent reduction, which was not statistically significant.
However, in analyses of subgroups of participants, researchers found that women who were most compliant about taking the supplements experienced a significant 29 percent decrease in hip fractures. And women 60 and older had a significant 21 percent reduction in broken hips.
The most common adverse effect of the supplementation was kidney stones, which were reported by 449 women in the supplement group, compared to 381 women in the placebo group.
"This all really points to the ability of women at highest risk for osteoporosis to make their own informed choices about supplements they take," said Jackson, associate professor of internal medicine and physical medicine at OSU Medical Center.