April 20, 2011 -- A year after Marie Hoffmann began menopause, a bone density test revealed signs of osteoporosis. Her doctor started her on the bone-building drug Fosamax and a calcium supplement, which helped strengthen her brittle bones and downgrade her condition to osteopenia.
Hoffmann, a 62-year-old from Kansas City, Mo., said she's happy with the results of her treatment -- and understandably so. Her mom and aunt both died because of complications from osteoporosis, she said. And for someone who never liked milk, calcium supplements seem a logical addition.
But new research may cause worry among some like Hoffmann. In an analysis of past research that has already sparked debate among medical experts, researchers suggests calcium supplements might boost the risk of heart attacks.
Using data from the Women's Health Initiative Calcium/Vitamin D Supplementation Study -- a seven-year trial in 36,282 postmenopausal women -- Dr. Ian Reid from the University of Auckland in New Zealand and colleagues concluded that women who took calcium supplements had a 13-to-22 percent greater risk of having a heart attack than women who did not. The risk went up regardless of whether the women also took vitamin D, which promotes calcium absorption and bone mineralization. The researchers also found a milder increase in stroke risk among women taking the supplements.
"When these results are taken together with the results of other clinical trials of calcium supplements, with or without vitamin D, they strongly suggest that calcium supplements modestly increase the risk of cardiovascular events, particularly myocardial infarction," Reid and colleagues wrote in the report published today in BMJ. "These data justify a reassessment of the use of calcium supplements in older people."
But the findings, which stem from a review of old data rather than new observations, conflict with earlier reports from the Women's Health Initiative (WHI).
"In other WHI analyses, we found no association between [calcium and vitamin D] supplementation and [coronary heart disease] or stroke death and neither did these authors," said Andrea LaCroix, a professor of epidemiology at the Fred Hutchinson Cancer Research Center and a co-author of the earlier WHI studies.
LaCroix says "exploratory" reviews of past studies can often lead to findings that result from chance alone. But Reid and colleagues argue that the heart attack risk went unnoticed in earlier investigations because so many study subjects were taking calcium supplements outside of the study.
Calcium Supplements Linked to Heart Attack Risk
In a smaller study of post-menopausal women in New Zealand, Reid and colleagues previously showed that calcium supplements taken without vitamin D boost heart attack risk in post-menopausal women by 27-to-30 percent. The new data broaden the picture to include women who take calcium and vitamin D -- a supplement combo that's steadily gaining in popularity, according to an April 13 report from the Centers for Disease Control and Prevention's National Center for Health Statistics.
"Vitamin D and calcium [supplements] are the flavors of the month and it's the impulsive nature of our society to get that quick fix instead of getting back to eating whole foods," said Dr. Stephen Cook, an internist at the University of Rochester Medical Center in New York.
More than half of American adults take at least one dietary supplement, according to the CDC report.
Along with her calcium supplement, Hoffmann takes fish oil and a multivitamin.
But some experts argue that eating a well-balanced diet makes supplements, which escape regulation by the U.S. Food and Drug Administration, unnecessary. Dairy foods are a good source of calcium, as are dark, leafy greens like spinach. And some cereals, juices and soy milk brands are also enriched with calcium.
"Calcium intake through the diet did not apparently add to the risk, so it may be safer to take calcium through the diet," said Dr. Bart Clarke, associate professor of medicine at the Mayo Clinic in Rochester, Minn. "For now, [I] would recommend that patients discuss taking calcium supplementation with their doctor, and that they make sure their dietary calcium is adequate if they choose not to take calcium supplements."
Dietary Supplements: Is There a Risk?
Hoffman called the study findings "mildly scary," but said she'll continue taking calcium supplements anyway.
"I mean, there have been so many different studies that have proved to not make a darn bit of difference, and one more doesn't upset me that much," she said. "I think the thought of osteoporosis upsets me more than the heart attack risk does."
Dr. Harlan Krumholz, associate professor of medicine at Yale University School of Medicine in New Haven, Conn. said more research is needed to uncover the health risks, if any, tied to calcium supplements.
"The assumption should not be that they can't hurt and might help," Krumholz said. "We should all want strong evidence of benefit and assurance of safety before making choices to take supplements."