To help determine if the results of a study designed to analyze the cardiovascular effects of calcium supplements would have been different if it involved people taking both vitamin D and calcium, researchers analyzed data from a Women's Health Initiative (WHI) study that included women who took both calcium and vitamin D.

The WHI researchers' 2007 analysis of the data found no association between cardiovascular events, such as heart attack, and supplement use. That investigation, however, didn't distinguish between women taking calcium and vitamin D prior to the study—54 percent of the participants—and those who began taking supplements at the start of the study.

In the new look at the data, the New Zealand research team found that women taking calcium supplements for the first time, with or without vitamin D, raised their risk of heart attack and stroke by 16 percent. Paradoxically, those who took calcium and vitamin D on top of the calcium supplements they were already taking did not face a greater risk of heart attack or stroke. In fact, their chances of dying during the WHI study dropped by 16 percent.

But if calcium really does increase the risk of heart attack and stroke, why didn't the group that took the most suffer the most? There are other questions as well. For example, in the 2010 study, the increased risk of heart attack began at a median dose of only 805 mg—about 400 mg short of the total daily amount of calcium most major health organizations recommend for older adults.

Does this mean that short-term supplement use at moderate doses might be enough to increase women's risk of heart attack—particularly if they have extensive plaque build-up, as many older women do?

What to do?

Clearly, the need for more studies to definitively answer these questions makes it unlikely that these findings will be the final word. In the meantime, keep these points in mind:

First, it's important to note that the potential cardiovascular risks of calcium apply to supplements alone, not the calcium you consume naturally through diet. In fact, studies have linked high-calcium diets to low rates of heart disease. And the National Osteoporosis Foundation notes that food—not supplements—is your best source of calcium. This may be because calcium supplements acutely raise the amount of calcium in your blood—more so than the ingestion of calcium from food sources, which are absorbed from the GI tract more slowly.

Getting sufficient calcium without taking a supplement is not as hard as it might sound. Unlike vitamin D, for which supplements are generally needed by older adults who do not receive adequate sunlight exposure, it's much easier to meet your daily calcium requirements—1,200 mg if you’re 50 or over—from food sources such as salmon, broccoli, dairy products (such as milk or yogurt) and calcium-fortified foods.

Second, your bones won't accrue any additional benefit if you exceed the recommended daily dosage of calcium. Plus, potential cardiovascular risks aside, consuming that additional calcium via a supplement may increase your risk of other problems, such as kidney stones.

Third, if you have osteoporosis or osteopoenia (pre-osteoporosis), if you are severely calcium deficient or if you can't consume a sufficient amount of calcium through diet, the benefits of taking a daily calcium supplement may outweigh the potential risk of cardiovascular disease. Still, it's reasonable to talk to your doctor, particularly if you have heart disease or are at high risk for developing it.

Doctor's Viewpoint

Erin Donnelly Michos, M.D. Assistant Professor of Medicine Division of Cardiology Johns Hopkins Hospital

We need more studies to clarify the potential risk of calcium supplements. If you have osteoporosis or a calcium-deficient diet, you may need calcium supplements along with vitamin D to strengthen your bones. However, you shouldn't rely on calcium supplements as your sole preventive treatment.

Bisphosphonate drugs are more powerful bone builders for those at high risk of fracture. If your fracture risk is low, engage in weight-bearing exercise and get calcium through your food.

Source: Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 07 Jul 2013

Last Modified: 15 Jan 2015