Harvard Heart Letter

Another yellow light for calcium supplements

Millions of women and men take calcium pills to strengthen their bones and ward off osteoporosis. Whether taking calcium is good, neutral, or bad for the heart is a matter of conflicting studies and lively debate. Australian researchers have sounded another note of caution in a controversial paper they published in the medical journal BMJ.

The Australian team took a fresh look at data from the Women's Health Initiative Calcium–Vitamin D Supplementation Study. It randomized 36,282 women to a calcium–vitamin D supplement or to a placebo. The results of the trial, published in 2006, showed a small improvement in hip bone density but no effect on hip fracture. The researchers reported that the numbers of heart attacks and other cardiovascular problems were the same in both groups.

A big flaw in the trial was that half of the women, including half of those taking the placebo, were taking calcium supplements on their own. To account for this extra calcium, the Australian researchers re-analyzed the data, looking mainly at the 16,718 women who were not taking a personal calcium supplement. In this group, women randomized to the calcium–vitamin D pill had a 20% higher risk of having a heart attack during the study and a 17% higher risk of having a stroke, compared with women taking the placebo (BMJ, published online April 19, 2011).

To continue reading this article, you must login.
  • Research health conditions
  • Check your symptoms
  • Prepare for a doctor's visit or test
  • Find the best treatments and procedures for you
  • Explore options for better nutrition and exercise
Learn more about the many benefits and features of joining Harvard Health Online »