Controversial studies add to growing concern about calcium supplements and cardiovascular risk
For years, women and men at high risk for osteoporosis have been urged to take calcium supplements. Without sufficient calcium, your bones become brittle and prone to fracture. But some research suggests that the added protection calcium supplements offer your bones might come at the expense of your heart.
Why might excess calcium be risky? Experts don't know for sure, but calcium is a component of arterial plaquescholesterol-rich substances that can build up within the walls of your arteries, impairing artery function and raising blood pressure. If a plaque ruptures, a blood clot can form and lead to a heart attack or stroke.
For those individuals undergoing dialysis, calcium supplements may pose additional concern. Because your kidneys have trouble eliminating calcium, you're already at high risk for calcium deposits (calcifications). Calcium supplements may increase your risk of these calcifications and therefore increase your risk of cardiovascular disease.
Women and calcium
For women over age 50, a link between calcium supplements and cardiovascular disease is particularly troubling because many women start taking calcium supplements as they approach menopause. The calcium boost provided by supplements protects against osteoporosis.
However, as women go through menopause, their risk for heart disease also substantially increases. Researchers have therefore wondered whether taking calcium supplements could potentially put women at greater risk of developing arterial plaques at a time when they are most vulnerable to heart disease.
In a trial designed to analyze the cardiovascular effects of calcium supplements, researchers at the University of Auckland, New Zealand, assigned 1,471 postmenopausal women to take 1,000 mg of calcium or a placebo daily. The results, published in BMJ (British Medical Journal) in 2008, showed that after five years, women taking calcium were 47 percent more likely to die suddenly or suffer one or more heart attacks or strokes than women in the placebo group. At this rate, the researchers estimated that 50 women would need to take calcium supplements for five years to prevent one bone fracture, while just 44 women would need to take it for the same duration to cause one heart attack. Although the findings were troubling, the data were statistically insignificant and therefore weren't cause for alarm.
In a 2010 review of 11 clinical trials on calcium and bone loss involving nearly 12,000 women, the same researchers found a 27 percent increased risk of heart attack in women taking calcium supplements compared with those taking a placebo. Unlike the 2008 study, however, they found no increase in stroke or death among women taking calcium.
Given the somewhat contradictory results, the medical community was left with more questions than answers. For example, if calcium were to blame for a higher rate of heart attack, why wasn't there a higher mortality rate in the calcium group?
Would the results have been different if the researchers had looked at studies involving people taking both vitamin D and calcium? Vitamin D supplements have been linked to a lower risk of heart attack and stroke, and it's very uncommon for someone with or at risk for bone loss to take only calcium.
Source: Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50