Many people who take corticosteroids for inflammatory forms of arthritis also take calcium supplements to prevent bone loss and fracture. But there is evidence the supplements can increase risk of heart attack and stroke, according to a study released online in 2011 in the BMJ.

“The study suggests that calcium supplements do more harm in the form of heart attacks and strokes than they do good in the form of fractures prevented,” says lead author Ian Reid, MD, professor of medicine and endocrinology at the University of Auckland in New Zealand.

"We should get calcium from food, as dietary calcium does not appear to increase the risk of heart disease," he adds.

The evidence raises questions for millions of older women who take calcium supplements to keep bones strong and help ward off osteoporosis. And it may be of particular concern for those on corticosteroids, which decrease absorption of calcium by the intestines while increasing excretion of calcium through the kidneys.

Dr. Reid and other medical experts agree it’s important to talk to your doctor about your specific calcium needs, what supplements you take – for instance, if you take a multivitamin and a calcium supplement – and what your diet generally includes. These factors can impact your doctor’s recommendation.

What the Studies Show

In 2007, researchers from the Women's Health Initiative Calcium/Vitamin D Supplementation trial reported no increase in heart risks associated with calcium supplements among more than 36,000 women followed for seven years. But more than half of the women in the study were taking calcium supplements on their own before the trial began, which might have masked the findings.

So Dr. Reid and colleagues looked only at the subset of 16,718 women who had not been taking supplements at the start of the trial. Results showed that among this group, those assigned to take calcium and vitamin D had a 13 to 22 percent higher risk of heart attack and stroke. Women taking placebo had no increase in risk.

Further analyses that incorporated data from 13 other trials involving a total of about 29,000 women showed consistent findings. Overall, women taking supplements were at about 25 to 30 percent increased risk for heart attack and 15 to 20 percent increased risk for stroke.

"In our analysis, treating 1,000 patients with calcium or calcium and vitamin D for five years would cause an additional six [heart attacks] or strokes and prevent only three fractures," Dr. Reid says.

The researchers hypothesize that the sudden spike in blood calcium levels when starting a supplement causes a lying down of calcium in the artery walls that leads to hardening of the arteries, a major cause of heart attack and stroke.