TUESDAY, Jan. 15, 2008 (HealthDay News) -- The calcium tablets taken by millions of postmenopausal women to reduce their risk of osteoporosis may be contributing to an increase in heart attack and other cardiovascular problems.
The findings might mean doctors shouldn't prescribe the supplement so freely.
"There are data from other recent studies showing an upward trend in heart attacks with calcium use, so we think this is likely to be a real finding," said study senior author Dr. Ian Reid, of the faculty of medical and health sciences at the University of Auckland in New Zealand. "It is likely that this is primarily a problem for elderly women, because they are more likely than younger subjects to have prevalent coronary heart disease. Therefore, it seems wise to advise against calcium supplementation in those over the age of 70 years and in those known to have coronary heart disease."
"This is the most upsetting study. Osteoporosis is a major issue that we're trying to deal with as we get older, and we've been talking about calcium supplementation to prevent osteoporosis," added Dr. Susan Steinbaum, director of Women and Heart Disease at the Heart and Vascular Institute at Lenox Hill Hospital in New York City. "There's a huge group of women trying to stay healthy [by taking calcium], and now we're being told that, in fact, this is something that can hurt you... It's very, very frustrating."
Steinbaum added, however, that while the results can't be ignored, the study may not be large enough to justify taking women off calcium supplements just yet. "Preventive medicine is not something that can be standardized per person," she said. "It needs to be individualized."
The pharmaceutical industry does not necessarily agree with these points.
In a statement, Pamela Mason, a nutritionist and spokeswoman for the Health Supplements Information Service, which is funded by several pharmaceutical companies, said, "Calcium is an essential mineral, vital for bone health and nerve and muscle function. The results of this study certainly do not suggest that people should lower their calcium intakes below the RDA (Recommended Daily Amount). Indeed, because of the importance of calcium, it remains imperative for people to achieve the RDA."
Still another expert weighed in on the study's importance.
"This suggests very weakly that these other effects of calcium supplementation need to be paid attention to. It's a very good study in that sense," said Dr. Bernard Roos, director of geriatrics research at the University of Miami Miller School of Medicine and the Miami VA. "The effect they're reporting is very small. I don't believe that it should change people's behavior. I believe the conclusion that they drew is fair: This should just alert you to the possibility that it's a potentially detrimental effect."
Roos also pointed out that healthy postmenopausal women, such as those participating in this analysis, would not be expected to be taking calcium anyway. "Healthy postmenopausal women, by definition, don't have osteoporosis, so if you don't have osteoporosis, why are you so worried about taking anything if you're healthy?" he said.
Prior evidence had indicated that calcium supplementation might protect against vascular disease, because it increases the ratio of HDL or "good" cholesterol to LDL or "bad" cholesterol by almost 20 percent. There is also evidence that calcium reduces blood pressure (albeit only briefly). And people who live in areas with calcium-rich water seem to have a lower risk of cardiovascular problems.
But the overall evidence, especially in older women, is inconsistent, stated the study authors.
And any negative heart effect would have to be taken seriously given that postmenopausal women have a higher incidence of vascular disease anyway.
This analysis looked at 1,471 postmenopausal women with a mean age of 74 who had previously participated in a study looking at the effects of calcium on bone density and fracture rates. The findings were expected to be published online Jan. 16 in the BMJ.
All women had been randomly assigned to receive either calcium or a placebo.
Women in the calcium group had slightly more than twice the risk of having a heart attack compared with women taking the placebo.
Women taking calcium had a 47 percent higher risk of having any one of three "events" (heart attack, stroke or sudden death) than women in the placebo group.
The authors then took the unusual step of checking hospital admissions and reviewing death certificates to find any previously unreported events.
When these were added to the mix, the relative risk of having a heart attack or one of the composite events decreased somewhat, though women taking calcium were still at a higher risk. Now women taking calcium had a 49 percent greater risk of having a heart attack and a 21 percent higher risk of having one of the three composite events.
The findings seem odd in light of calcium's beneficial effect on cholesterol. Yet the supplement has also been found to elevate blood calcium levels, which could speed up calcification of the blood vessels. Previous research has found that calcium build-up in the arteries can foreshadow coronary artery disease.
"There is a point here that is even more subtle, which is that lipids are not the only factors that are giving you cardiac risk," Roos said.
The picture is even further complicated by the fact that calcium is often taking in conjunction with a class of drugs known as bisphosphonates. Earlier this month, the U.S. Food and Drug Administration issued an alert regarding the possibility of severe and sometimes even incapacitating bone, joint and/or muscle pain in patients taking these drugs.
What's a woman to do? Probably nothing right just yet, although physicians might start weighing the risks of calcium supplementation more carefully.
Having the equivalent of four servings of dairy products "seems sensible in these subjects," Reid said. "There is no reason, on the basis of [this study], to be advising reduced calcium intakes in children, adolescents, or young and middle-aged adults."
Visit the National Osteoporosis Foundation for more on calcium and bone health.