The Women's Health Initiative has followed more than 150,000 post-menopausal women for more than to a decade. The continuing study has yielded results about estrogen replacement therapy, hip fracture risk, and now, the effect of calcium and vitamin D supplements on heart disease.

Dr. Judy Hsia leads the Initiative for George Washington University hospital in Washington, DC. She says many women take calcium and vitamin D to strengthen their bones, and researchers wondered if the supplements might have other effects. "Because we were tracking all these women for this prolonged period of time, we also looked at other outcomes," she explains, "one of which was whether calcium and Vitamin D prevented heart disease or maybe made heart disease worse."

There have been arguments on both sides of that question. Past research has indicated that calcium can contribute to the buildup of coronary artery blockages. But other research shows that women taking calcium and vitamin D have better weight control and lower blood pressure, reducing those risk factors for heart disease.

Hsia says there were 36,000 women in this part of the study, ranging in age from 50 to 79 years old. For seven years, half took supplements of 1,000 milligrams of calcium with 400 international units of vitamin D. The other half took a placebo pill that looked the same. "And we counted up the number of heart attacks and coronary deaths and strokes in each treatment group and it turned out there was a balance." She says the numbers were essentially the same in the active treatment group and the placebo group.

So, she concludes, the many women around the world who take calcium and vitamin D to protect their bones shouldn't stop taking the supplements. "They don't need to worry that they may be making heart disease worse. On the other hand," she adds with a rueful laugh, "they cannot expect that these will improve their cardiovascular health either!"

But Hsia also says the supplements may not have much impact on bone strength. Researchers found that while taking calcium and vitamin D increased bone density in women, it really didn't reduce the incidence of hip fracture. She suggests that the recommended amount of vitamin D may be too low, and should be studied further. The results appear in Circulation, the Journal of the American Heart Association.