The study – published in Heart – questions the safety of calcium supplement pills, suggesting that the mineral causes changes in blood vessels that could lead to twice the risk of heart attack.
"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," said the researchers, led by Professor Sabine Rohrmann, from Zurich University's institute of social and preventative medicine.
"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," they added.
Rohrmann and her team argued: "We should return to seeing calcium as an important component of a balanced diet, and not as a low cost panacea to the universal problem of postmenopausal bone loss."
However many others have been keen to point out the importance of calcium for bone health: “The bottom line is consumers need calcium, and particularly for theelderly, who are at such great risk of falls and fractures due to weak bones, removing calcium supplements from their diets could put them at even greater risk for those kinds of problems,” said Dr Taylor Wallace, senior director, scientific & regulatory affairs, for the US-based Council for Responsible Nutrition (CRN).
Wallace said the study itself “is not reason enough to discount the important benefits of calcium.”
"Calcium is an important mineral with proven benefits for bone health and a long history of safe use backed by an extensive body of observational and clinical studies that supports its use for reducing the risk for osteoporosis and hip, bone and other fractures.”
Meanwhile, Natasha Stewart, senior cardiac nurse at the British Heart Foundation (BHF), noted that whilst the research indicates there may be an increased risk of having a heart attack for people who take calcium supplements ... “this does not mean that these supplements cause heart attacks.”
“Further research is needed to shed light on the relationship between calcium supplements and heart health,” said Stewart. “We need to determine whether potential risks of the supplements outweigh the benefits calcium can give sufferers of conditions such as osteoporosis.”
Rohrmann aqnd her colleagues base their findings on data from almost 24,000 participants from one of the German arms of the European Prospective Investigation into Cancer and Nutrition (EPIC) study – in Heidelberg.
All the participants, aged between 35 and 64, were quizzed about whether they regularly took vitamin or mineral supplements before having their health tracked for an average of 11 years.
During this time 354 heart attacks, 260 strokes, and 267 associated deaths occurred, said the researchers.
After taking account of factors likely to influence the results, those whose diets included a moderate amount (820 mg daily) of calcium from all sources, including supplements, had a 31% lower risk of having a heart attack than those in the bottom 25% of calcium intake, said Rohrmann and her team.
However those with an intake of more than 1100 mg daily did not have a significantly lower risk. There was no evidence that any level of calcium intake either protected against or increased the risk of stroke, which backs up the findings of other research, say the authors.
But when the analysis looked at vitamin and mineral supplements, Rohrmann found that those who took calcium supplements regularly were 86% more likely to have a heart attack than those who didn't use any supplements.
This risk increased further among those who used only calcium supplements – with this group more than twice as likely to have a heart attack as those who didn't take any supplements.
"This study suggests that increasing calcium intake from diet might not confer significant cardiovascular benefits, while calcium supplements, which might raise [heart attack] risk, should be taken with caution,” said Rohrmann and her team.
Volume 98, Issue 12, Pages 920-925, doi:10.1136/heartjnl-2011-301345
"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)"
Authors:Kuanrong Li, Rudolf Kaaks, Jakob Linseisen, Sabine Rohrmann