Everybody knows calcium is important. To boost their intake, more than 43 percent of Americans take calcium supplements, according to The Journal of Nutrition. But a study published in the journal Heart suggested that relying on calcium supplements—rather than getting enough of the mineral in one’s diet—might come with a cost, resulting in many stories linking the supplements with a higher risk of heart attack, stroke and overall cardiovascular mortality.
The National Institutes of Health Office of Dietary Supplements recommends that healthy adults between 19 and 50 consume 1,000 mg of calcium daily, and that women over 50 and men over 71 consume 1,200 mg daily. So how will the recent research impact the ways people get their calcium? We asked study author Sabine Rohrmann, PhD, MPH.
Natural Foods Merchandiser: Why do this study?
Sabine Rohrmann: We knew about the results of some clinical trials that observed an increased heart attack risk among those taking calcium supplements. We wanted to examine whether we also would see this effect in an observational study [in contrast to a clinical trial in which participants are assigned to taking a supplement or a placebo].
NFM: How did you do the research?
SR: We used data of a German cohort study (EPIC-Heidelberg with more than 25,000 participants). Participants were asked at baseline (1994 to 1998) about their diet and supplement use and were followed until 2010. Supplement information was assessed at regular intervals.
NFM: What did you find?
SR: Interestingly, we observed that those participants with a moderate intake of calcium from diet had a lower risk of heart attack than those with a low dietary intake. In contrast, those participants who regularly used calcium supplements had an increased risk of heart attack compared with non-users.
NFM: The study excluded people who already had a diagnosed heart attack or stroke. Why?
SR: We know that participants who have had a heart attack or stroke have a different health behavior than healthy people. They also have a different risk of having an additional stroke or heart attack. We were primarily interested in whether healthy participants who regularly take calcium supplements have a higher risk of heart attack or stroke.
NFM: What’s different about the way the body processes calcium found in food compared with calcium supplements?
SR: Previous studies have shown that high serum levels of calcium are related to an increased risk of myocardial infarction (heart attack). It is plausible that taking a high dose of calcium (instead of small amounts distributed over the day) may lead to an acute increase in the serum level of calcium. Instead, taking only small amounts does not cause a quick increase in calcium levels. There is more time for the body to absorb the mineral. This may, for example, have effects on vascular calcification.
NFM: Does this differ for men and women?
SR: The results are the same for men and for women. However, the question is probably more of interest for women as they use calcium supplements more frequently than men.
NFM: What happens as a person ages?
SR: We have no indication of an age effect. However, our study is too small to look at this in detail.
NFM: Is there a certain amount of supplemental calcium that seems to be safer?
SR: This is another question we cannot answer. Clinical trials, which have also shown an increase in risk, usually used 1,000 mg per day. So, further studies should study the effect of supplements with 250 or 500 mg.
NFM: What should consumers and retailers learn from this?
SR: Calcium supplements have long been recommended for bone health, for example, to prevent osteoporosis. However, it turned out that we probably do not need mega-doses of calcium. The current recommendation—about 1,000 to 1,200 mg per day—can be met by eating a balanced diet that includes (low-fat) milk and dairy products. However, some older people do not tolerate milk and dairy products well and thus take calcium supplements. In this case, it might be good to use a mineral water that is rich in calcium and eat calcium-rich plant foods, such as some kinds of cabbage. As a nutritionist, I would have given the same advice before I knew about our study results. I believe we recommend too quickly that people take supplements instead of having a closer look at a person’s diet. More and more, we realize that mega doses of supplements—minerals and vitamins—can cause harm.
Supplementation important for some
Heather Bainbridge, a registered dietitian at Columbia University Medical Center, said that the Heart study will cause her to more carefully consider recommending calcium supplements. “I always first look to see how a patient’s overall dietary calcium intake is,” she says. “Now I’m going to take more time.”
The study won’t stop her from telling people to take supplemental calcium if they have a hard time getting it into their diets, though. “Observational studies are helpful but they don’t show causation,” she says.
Bainbridge points out that people who get their calcium from supplements rather than from whole foods might be missing nutrients elsewhere in their diets—and that this could have been a misleading factor in the study.
“It might be that they’re not only missing the calcium but not meeting their needs for overall nutrients, too,” she says. When we consume an apple, she said, we benefit from the whole apple’s systemic effects. But when we extract one nutrient and consume it out of context, “we might not be getting all of the benefits we get when we take in the whole food source.”
Rohrmann, meanwhile, said that the study didn’t look at the effects of different amounts of supplemental calcium. “Clinical trials, which have also shown an increase in risk, usually used 1,000 mg per day,” she said. “So, further studies should study the effect of supplements with 250 or 500 mg.”