Are calcium supplements bad for the heart?

Based on a new study, calcium supplements may increase the risk of having a heart attack. Experts criticize that the study’s design is not sound enough to draw such conclusions.

The observational study analyzed data from 23,980 people, aged 35–64 years, in the German cohort of the European Prospective Investigation into Cancer and Nutrition Study (1). The participants’ calcium intake was assessed using food frequency questionnaires and their cardiovascular health was tracked for an average of 11 years. The study results showed that those whose diets included a moderate amount (820 mg daily) of calcium from all sources, including supplements, had a 31% lower risk of heart attack than those with the lowest calcium intake. Participants with an intake of more than 1,100 mg daily did not have a significantly lower risk. There was no observation that any level of calcium intake either protected against or increased the risk of stroke. When the analysis looked at vitamin/mineral supplements, it found that those who took calcium supplements regularly were 86% more likely to have a heart attack than those who did not use any supplements.

The researchers concluded that increasing calcium intake in the diet might not confer significant cardiovas-cular benefits, while calcium supplements might raise heart attack risk, and thus, should be taken with caution. They speculate that supplements may cause calcium levels in the blood to soar above the normal range, and this flooding effect might be harmful.

Experts criticized that calcium intakes were only measured once at the start of the study: It would be inconceivable that people had remained on identical diets for 11 years. Therefore, a strong possibility exists that diets evolved – and calcium intakes fluctuated – during the follow-up period. While the study excluded people with a history of heart attack and stroke, other cardiovascular risks, e.g., blood pressure, cholesterol, were not evaluated at the start of the study. It is possible that people with existing health problems changed their diets or supplement use over the course of the study. In addition, the study identifies users of calcium supplements but does not reveal the doses of calcium used. It is not known, for example, whether people were taking doses above, at, or below recommended intakes. Another issue, not mentioned by the authors, is the potential negative effect of low vitamin D intakes. Average daily intakes were 3.4 micrograms, much lower than the recommended daily allowance of 5 micrograms. The experts noted that mineral and vitamin supplements were never intended to treat chronic health conditions. Instead, their role is to help people meet recommended nutrient intakes. Calcium is important for good bone health. Unfortunately certain groups fall short of their daily calcium needs as well as other nutrients. As a result, taking a supplement with calcium can bridge this gap.

1. Li, K. et al. Associations of dietary calcium intake and calcium supplementation with myocardial infarction and stroke risk and overall cardiovascular mortality in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition Study (EPIC-Heidelberg). Heart. Published online May 2012.