Calcium pills that are widely used to help prevent osteoporosis have been associated with a significantly increased risk of heart attack, researchers report.
Many people, especially postmenopausal women, take calcium supplements to help ward off osteoporosis. But a new study by researchers at the German Cancer Research Center in Heidelberg has turned up disturbing evidence that these supplements may significantly increase the risk of heart attack, potentially outweighing their beneficial effect on bone health.
The authors of the study, which was published online on May 23, 2012, in Heart, set out to prospectively test for associations between calcium intake and the risk of a number of adverse cardiovascular effects. To do so, they looked at data from 23,890 participants in a German cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Participants were between the ages of 35 and 64 and free of major cardiovascular disease events at the time of recruitment, which took place between 1994 and 1998. When they enrolled in the study, participants provided a range of health information as well as a description of their diet over the previous 12 months, including use of supplements.
The average follow-up time for participants was 11 years. Compared with those who used no supplements, risk of heart attack was increased 86% for regular users of calcium supplements and 139% for those who used only calcium supplements. However, there was no statistically significant association between use of calcium supplements and risk of stroke or mortality due to cardiovascular disease. The researchers note that the association between increased heart attack risk and use of calcium supplements could be due to the acute increase in serum calcium that occurs after taking calcium supplement pills but not after eating foods rich in calcium.
The results also gave some indication that increased dietary intake of calcium was associated with a decreased risk of heart attack. Compared with those in the lowest quartile of intake, those in the third quartile of dietary calcium intake (an average of 820 mg per day) had a risk of heart attack reduced by 31%. When participants were broken down by sex, this reduction in risk was non-significant for men, but even more significant for women, at 57%. The researchers propose that the reduced risk could be due to uncontrolled confounders for women but not men or to the beneficial effect of other nutrients contained in dairy products.
The researchers note that 2 recent meta-analyses have also indicated that using calcium supplements may lead to increased risk of heart attack. The authors of an accompanying editorial, Ian Reid, MD, and Mark Bolland, PhD, of the University of Auckland in New Zealand, point out that other studies have found a link between use of calcium supplements and kidney stones as well as gut and abdominal symptoms. Given that those who take calcium supplements are healthier than average and that the supplements offer only a modest benefit in terms of protecting against osteoporosis, the editorial authors question whether patients should take them.
"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 write. “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.”