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.

The Safest Way to Get Calcium

Doctors say further study is needed before firm conclusions can be drawn about the safety of calcium supplements. Still, they agree that getting calcium from diet is probably best.

"Calcium obtained from a meal is slowly absorbed," and does not negatively impact the arteries, Dr. Reid explains.

"The findings made me rethink what I tell my patients," says Susan V. Bukata, MD, associate professor of orthopedic surgery at the University of Rochester Medical Center in New York.

Since the Institute of Medicine recommends 1,200 milligrams (mg) of calcium a day for most women aged 50 and older, "my reflex has always been to prescribe a 1,200-mg supplement to these patients. Now I work with them to increase calcium in their diet. In many cases, I can cut the supplement to 600 mg, which presumably cuts heart risks," she says.

Dairy products, green leafy vegetables, and supplemented juices, breads and cereals are all good sources of calcium.

Supplements for Some

Scott J. Zashin, MD, clinical assistant professor in the rheumatology division at the University of Texas Southwestern Medical Center in Dallas, agrees calcium is best obtained from food but that supplements may be fine for certain populations.

"As with most things, one size does not fit all. Supplements are probably safe for a woman with few heart disease risk factors. But for a woman at high risk, it may be better to avoid supplements if possible," he says.

Kenneth G. Saag, MD, MSc, associate professor of medicine in the division of clinical immunology and rheumatology at the University of Alabama at Birmingham, agrees that supplementation needs to be individualized.

People who are taking corticosteroids, who have chronic inflammatory disorders such as inflammatory bowel disease or who are otherwise at high risk for losing extra calcium may need 1,500 mg of calcium daily, Dr. Saag says.

He thinks many people in his practice are "over-supplementing. They are getting calcium from supplements, from multivitamins, from [supplemented] foods and so on, and they end up taking more than the recommended amount. The onus is on the patient and the doctor to sit down and see how much calcium the patient is actually getting and avoid over-supplementation," he says.