Because calcium and vitamin D supplements have been associated with improvements in bone health, many women take these supplements to protect their bones as they age. But is calcium and vitamin D supplementation as protective against osteoporosis as many women hope it to be? Some studies suggest it can slow bone loss and reduce the risk of falls in older women, but others show no protective benefit.

A new study in the February 16, 2006 issue of the New England Journal of Medicine investigated whether daily calcium and vitamin D supplementation reduces the risk of hip fracture in postmenopausal women. The researchers could not confirm that the supplements reduced the risk of hip fracture, but they did notice a small improvement in bone density.

About the Study

This study was part of the Women’s Health Initiative and included 36,282 postmenopausal women who were ages 50-79 when the study began. Half of the women were assigned to receive daily supplements containing 1,000 milligrams of calcium carbonate and 400 international units (IU) of vitamin D, and the other half were assigned to receive a placebo. For an average of seven years, the researchers tracked whether the women had hip fractures. In addition, a subgroup of 2,431 of the women underwent bone density testing when the study began and every three years thereafter.

A total of 175 hip fractures occurred during the study. The women in the supplement group had a 12% reduction in risk of hip fracture, but this finding was not statistically significant compared with the placebo group. However, when the researchers looked only at participants who took at least 80% of their study medication, they found that supplementation was associated with a significant 29% reduction in the risk of hip fracture. Furthermore, women over age 60 had a significant 21% reduction in hip fracture. In the subgroup that underwent bone density testing, the supplement group had 1% higher bone density than the placebo group. While the supplements were generally safe, they were associated with a 17% increased risk of developing kidney stones.

These findings have a few major limitations. First, the doses of calcium and vitamin D were conservative and may not have been large enough to reduce the risk of fracture. Second, the majority of the women in the study were not deficient in calcium and vitamin D; women who are deficient may benefit more from supplementation. Finally, the rate of hip fractures was about half of what was expected, which may have decreased the power of the study to detect a significant effect.

How Does This Affect You?

Although this study does not provide a definitive answer as to whether calcium and vitamin D supplementation reduces fracture in women, its findings indicate that supplementation may be beneficial in older postmenopausal women. Women should aim to consume the recommended levels of calcium and vitamin D, especially after menopause. It is recommended that women over age 50 consume at least 400 IU of vitamin D (600 IU for women over age 70) and 1,200 milligrams of calcium daily. If your diet does not provide this, supplements may help.

In a related study, published in the same issue of the Journal , researchers found that the calcium and vitamin D supplementation had no effect on the risk of colorectal cancer in the same group of women. It is important to get enough calcium and vitamin D from diet, supplements, or both, but contrary to what supplement manufacturers would like you to believe, supplements are not terribly protective against osteoporosis and other diseases, particularly in women who are not deficient in these nutrients.