WEDNESDAY, May 23, 2012 (HealthDay News) -- Many older Americans take calcium supplements to prevent bone loss, but they may be significantly increasing their risk for a heart attack, a new study suggests.
These supplements do not help prevent heart attacks or stroke as some previous research has suggested, the study authors say. But dietary calcium might reduce the risk, they noted.
"While a moderately high intake of calcium from diet may go along with a lower risk of heart attack, this is not true for supplementary calcium intake," said lead researcher Sabine Rohrmann, from the division of cancer epidemiology and prevention at the Institute of Social and Preventive Medicine at the University of Zurich in Switzerland.
"Instead of taking calcium supplements, men and women who want to increase their calcium intake should rely on foods, such as low-fat dairy products or mineral water, [that are] rich in calcium," she said.
The report was published online May 23 in the journal Heart.
For the study, Rohrmann's group collected data on nearly 24,000 people from Heidelberg, Germany, who took part in the European Prospective Investigation into Cancer and Nutrition study.
All of the participants were between the ages of 35 and 64 when they joined the study between 1994 and 1998.
Researchers asked them about their diet and whether they took vitamin and/or mineral supplements.
Over an average 11 years of follow-up, there were 354 heart attacks, 260 strokes and 267 deaths from cardiovascular causes among all participants, the researchers noted.
Participants whose calcium intake from all sources was moderate -- 820 milligrams (mg) a day -- had a lower risk of heart attack than those whose intake was less, the investigators found.
However, those whose intake was more than 1,100 mg did not have a substantially lower risk. In addition, there was no amount at which calcium was tied to a decreased risk of stroke.
When Rohrmann's team looked specifically at calcium supplements, they found an 86 percent increase in heart attacks among people who took them regularly compared to those who didn't take any supplements.
However, Dr. Robert Recker, director of the Osteoporosis Research Center at Creighton University and president of the National Osteoporosis Foundation, disagreed with the results.
"I am doubtful of these findings," he said. "It's hard to understand why calcium in the diet can reduce the risk of heart attack, but supplements increase the risk."
Recker said he thinks the findings could reflect a bias where those already at risk for heart attacks took supplements in hopes of reducing the risk, but some had heart attacks nonetheless.
Because the mechanism can't be described, the findings may be flawed, he noted.
Recker added that calcium supplements do prevent a significant number of fractures. "In the United States, the incidence of fractures from osteoporosis is greater than the combined incidence of heart disease, heart attack and stroke," he said.
He recommended taking a calcium supplement only if you aren't getting enough calcium from your diet. If you don't eat a lot of dairy products, Recker advised taking two separate doses of 500 mg of calcium a day.
But Dr. Ian Reid, a professor of medicine and endocrinology at the University of Auckland in New Zealand and author of an accompanying journal editorial, said the findings are similar to his own study.
"This study provides confirmatory evidence that calcium taken as supplements appears to increase the risk of heart attacks; whereas having a diet that has some calcium-rich foods doesn't seem to confer the same risk," he said.
Reid suggested that high doses of calcium might damage the walls of blood vessels, which leads to heart attacks.
"Most people should not be taking calcium supplements," he said. "You should get the calcium you need from your diet rather than taking supplements."
In terms of reducing fractures, Reid said that based on his study, which appeared online in the journal BMJ in July 2010, calcium supplements may reduce fractures 10 percent, but can increase the risk of heart attacks 25 percent.
He said his study showed that if 1,000 people are given calcium for five years, there will be 26 fractures prevented but there will also be 14 heart attacks, 10 strokes and 13 deaths.
Commenting on the new study, Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, added that "it has been hypothesized that abrupt changes in concentrations of calcium in the blood with calcium supplementation might be contributing to adverse cardiovascular effects."
So, he stated, "while further studies are needed, calcium supplements should be used only in those where the potential benefits outweigh the potential risks."
While the study found an association between calcium intake and heart attacks, it did not prove a cause-and-effect relationship.
For more about calcium supplements, visit the U.S. National Institutes of Health.