Although there has been significant debate about whether calcium and vitamin D supplements are beneficial for older women, new research suggests that the answer may be yes for those who are taking hormone replacement therapy.
Women using HRT who also took daily supplements of calcium and vitamin D saw a 40 percent reduction in their rate of hip fractures compared to women who took placebo supplements, according to the study.
"We found that women who were on hormones had less hip fractures, and women who were on hormones and calcium and vitamin D supplements had even fewer hip fractures," said study author Dr. John Robbins, a professor of medicine at the University of California at Davis.
Results of the study were published online June 26 in the journal Menopause.
As many as half of all women over 50 will have an osteoporosis-related fracture in their lifetime, according to the U.S. Preventive Services Task Force (USPSTF). Osteoporosis is a condition caused by a loss of bone mass and density, which leaves bones fragile and more susceptible to fractures. Calcium is an important component in bone growth, and vitamin D helps the body absorb calcium.
What's not clear is if supplements of these nutrients are as helpful in keeping bones strong as they are from natural sources, such as diet. The USPSTF recently looked at the effect of 1,000 milligrams of daily calcium and 400 international units of vitamin D. In February, they concluded that women shouldn't take calcium and vitamin D supplements because the available evidence wasn't strong enough to show a significant benefit. They added that the benefits of higher doses are unknown.
The new study included data from the Women's Health Study on about 30,000 postmenopausal women between the ages of 50 and 79. Many of the women were taking hormone replacement therapy -- either estrogen alone or a combination of estrogen and progesterone.
Just over 16,000 women participated in the calcium and vitamin D portion of the study. They were randomly selected to receive either a placebo or 1,000 milligrams of calcium and 400 international units of vitamin D each day. The average follow-up time was about seven years.
The hormone therapy and the supplements together were the most effective treatment for reducing hip fracture risk. The researchers found that the combination reduced the risk of hip fracture by 57 percent.
Overall, the rate of hip fracture was 11 per 10,000 women per year for those who took both hormones and supplements. Women who took only hormones had a hip fracture rate of 18 per 10,000, while those who took only supplements had a hip fracture rate of 25 per 10,000. Women who received neither therapy had 22 hip fractures per 10,000 women.
The researchers weren't able to tease out whether vitamin D or calcium had any benefits on their own. All of the women who took one supplement also took the other.
The study also was unable to find an optimal dose to help prevent hip fracture, although it appeared that women with a calcium intake of 1,200 milligrams and higher (from diet and supplements) might garner more benefit, Robbins said. The researchers saw a similar trend in lower hip fracture rates for women with higher vitamin D intake.
"In moderation, I think there's relatively little risk of harm from calcium or vitamin D," Robbins said.
"If a woman is taking hormones and other bone-enhancing drugs, she should also take calcium and vitamin D supplements in moderation or get them from dietary sources," he said.
Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center in New Hyde Park, N.Y., agreed that there doesn't appear to be a significant downside to taking these supplements if a woman doesn't have side effects, such as constipation, from taking them.
"We can get a lot of calcium from our diet, and that's probably the best way to get it," Rabin said. "But if you can take a supplement without ill effects, you can certainly continue. And women considering taking hormone therapy might also want to add supplements."
But, she added, the question of whether vitamin D and calcium can provide a significant reduction in fracture risk in women still needs more study. "The question hasn't been answered yet," she said.
As for hormone therapy, which is often prescribed for symptoms of menopause, doctors recommend the lowest possible dose for a short period of time. Use of hormone therapy has been linked to a variety of health problems, including risk of breast cancer, stroke and blood clots, according to the USPSTF.