Taking calcium supplements increases the risk of having a heart attack, Swiss and German researchers reported Wednesday. The finding adds to the growing body of evidence that such supplements increase the risk to those who take them while providing only minimal benefits. The study is considered important because large numbers of people, especially elderly women, continue to take the supplements in hopes of minimizing loss of bone density. The body of evidence now seems to suggest that calcium consumed as part of a normal diet can, indeed, increase bone density and perhaps help lower blood pressure, but that supplements may be too risky for most people to take.
A team headed by epidemiologist Sabine Rohrmann of the University of Zurich studied almost 24,000 participants in a German arm of the European Prospective Investigation into Cancer and Nutrition. All participants were between the ages of 35 and 64 when they enrolled in the study between 1994 and 1998. Normal diets were assessed for the preceding 12 months and they were quizzed about whether they regularly took vitamin and mineral supplements.
Participants were then tracked for 11 years, during which the researchers recorded 354 heart attacks, 260 strokes and 267 deaths related to either heart attacks or strokes.
The team reported in the journal Heart that those who had a moderate amount of calcium in their diet (820 milligrams daily) had a 31% lower risk of having a heart attack than those in the bottom 25% of calcium consumption, but those with a daily intake of more than 1100 mg did not have a lower risk. There was no evidence that any level of calcium intake in the diet affected stroke risk.
But when the team considered supplements, they found that those who took calcium supplements regularly were 86% more likely to have a heart attack than those who used no supplements. For those who took only calcium supplements, and no others, the risk doubled.
In an editorial accompanying the report, Dr. Ian R. Reid and Dr. Mark J. Bolland of the University of Auckland in New Zealand note that earlier studies have shown similar, albeit smaller effects. Those studies were smaller, however, and researchers did not put tremendous amounts of faith in them. Other studies, they note, have also shown that calcium supplements increase the risk of kidney stones by about 20%, cause gastrointestinal symptoms (particularly constipation) and double the risk of being hospitalized with an acute abdominal condition.
They speculate that the different effects of calcium in food and in supplements is caused by how they are absorbed. Calcium in food is absorbed in relatively low doses over a period of time, while calcium supplements produce a spike of calcium in the blood that may be the source of problems.
“Calcium supplements have been widely embraced by doctors and the public, on the grounds that they are a natural and therefore safe way of preventing osteoporotic fractures,” they wrote. “It is now becoming clear that taking this micronutrient in one or two daily [doses] is not natural, in that it does not reproduce the same metabolic effects as calcium in food.”