"The increase [in risk] is, I would say, moderate," says Sabine Rohrmann, PhD, assistant professor of chronic disease epidemiology at the University of Zurich.
However, the actual number of heart attacks during the follow-up period was small, with 354 recorded.
The researchers found a link, or association, between calcium supplements and heart attack, but the study cannot show cause and effect.
The dietary supplement industry takes issue with the findings. "The study is not consistent with the total body of science," says Taylor Wallace, PhD, senior director of scientific and regulatory affairs for the Council for Responsible Nutrition.
The study is published in the journal Heart.
Calcium Supplements & Heart Attack Risk: Context
Over the years, research on calcium and heart health has produced mixed findings.
Some previous research has suggested calcium from the diet may lower the risk of high blood pressure, obesity, type 2 diabetes, stroke, and heart disease. Other studies have not found these effects.
Two other recent analyses, published in 2010 and 2011, have triggered warnings that calcium supplements might boost the risk of heart attack.
Calcium & Heart Attack Risk: Swiss Findings
For the new study, the researchers asked the men and women to complete food surveys. They interviewed them to ask about vitamin or mineral supplements.
When the men and women entered the study beginning in 1994 through 1998, they were on average in their early 50s.
During the follow up, the researchers also recorded 260 strokes and 267 heart disease deaths.
They found that a higher intake of dietary calcium reduced the risk of heart attack.
They divided the participants into four groups. Those in the third group, with the next-to-highest intake of calcium from the diet, had a 31% reduced risk of heart attack compared to those who ate the least.
However, they found different results when looking at calcium supplements. Those who took calcium supplements had an 86% higher risk of heart attack compared to those who never took them.
The new findings are at odds with those of many other studies, says Wallace of the Council for Responsible Nutrition.
He also points out the relatively small number of heart attacks found in the study.
For calcium, he says, "We always recommend food first and then fill the gap with supplements," Wallace says. "The reality is, Americans don't get enough calcium."
Women past menopause are especially vulnerable to a low intake of calcium, he says. If someone is unable to get enough calcium from food, he says, "they should absolutely be taking a calcium supplement or they are at risk of developing osteoporosis or a fracture."
He points out some study limitations. "The original study wasn't designed to measure cardiovascular events," he says in a statement. As a result, risk factors for heart disease varied among groups. For instance, those in the calcium supplement group had a higher percentage of people with high cholesterol at the start of the study than other groups did.
Calcium & Heart Disease Risks: What to Do?
Pick calcium-rich foods over a pill, suggests Ian R.Reid, MD, distinguished professor of medicine at the University of Auckland. He wrote an editorial to accompany the study.
Taking a calcium supplement once or twice a day, he writes, "is not natural, in that it does not reproduce the same metabolic effects as calcium in food."
"The most important message to women who have been self-prescribing calcium," he tells WebMD, "is that they should cease this practice, and look to a modified diet to obtain adequate calcium."
In his own research, Reid has found a 25% increased risk of heart attack linked with calcium supplements.
''Everyone needs to discuss the calcium question with their own doctor," says Suzanne Steinbaum, DO, director of Women and Heart Disease at the Heart and Vascular Institute at Lenox Hill Hospital in New York. She reviewed the study findings for WebMD.
However, she says the new study findings suggest that taking a calcium supplement may not be the safest thing to do.
Understanding your individual risk for osteoporosis is important, she says. Calcium supplements are not the only way to boost bone health, she says. "We know a diet that has a moderate amount of calcium is safe and that weight-bearing exercise is protective."
The amount of daily calcium recommended by the Institute of Medicine varies by age and gender.
Women ages 19-50 and men ages 19-70 should get 1,000 milligrams daily. Women ages 51 and older and men over 70 should get 1,200 milligrams daily. A glass of milk has 300 milligrams of calcium.