Some calcium is good for the heart, but too much calcium through diet or a combination of diet and supplements can increase the risks of death from cardiovascular disease, according to a new study that looked at a large cohort of Swedish women.
This study found that high rates of calcium intake are associated with higher all-cause and cardiovascular death rates, but not deaths from stroke, reported Dr Karl Michaëlsson, a professor in the Department of Surgical Sciences, Section of Orthopedics, at Uppsala University in Uppsala, Sweden, and colleagues in an article published online February 13, 2013, in the British Medical Journal.1
The study is the latest in a series of analyses linking calcium intake and cardiovascular disease. Earlier this month, a National Institutes of Health–sponsored study2 found men who took 1000 mg or more of calcium per day were 20% more likely to die of heart-related causes than those who did not supplement with calcium. In that study, interestingly, the same risk was not found for women.
“In our observational cohort study,” said Dr Michaëlsson, “we found a higher risk of mortality, especially cardiovascular mortality associated with a high calcium intake.” He added, however, that the increase in risk was modest. After controlling for the dietary component of calcium intake, Dr Michaëlsson noted, there was on average no association with calcium supplement use and mortality.
The large study followed more than 61,000 women. During the median follow-up period of 19 years, there were nearly 12,000 deaths from all causes, of which about 3900 were from cardiovascular disease, 1900 from ischemic heart disease, and 1100 from stroke. The researchers estimated intakes of dietary and supplemental calcium from food frequency questionnaires that were available for nearly 39,000 women.
They found that women who consumed the largest daily amount of calcium (1400 mg or more) and who used supplement tablets had more than double the risk of death from heart disease, compared with those with intakes between 600 and 1000 mg, after controlling for physical activity, education, smoking, alcohol, and other dietary factors. On the other hand, they also found a higher risk of mortality associated with a low calcium intake (less than 600 mg), but this latter finding was not confirmed in a sensitivity analysis, said Dr Michaëlsson. There was no increased risk of mortality from strokes.
The authors noted that nearly two-thirds of middle-age and older American women take calcium supplements. But Dr Michaëlsson says “most American women don't need the supplements if they have a normal, varied diet that includes dairy and other sources of calcium. Supplements do not help prevent fractures.” In fact, he says a meta-analysis of randomized trials suggests that calcium supplements increase the risk of hip fracture.
So how does this affect how primary care physicians practice? “The use of calcium supplements is an ineffective way to prevent fractures if your patient has a normal diet,” says Dr Michaëlsson. “At worse, these supplements can do more harm than good. If your patient has a low calcium intake, however, you can recommend that she use calcium supplements.” Vitamin D supplements should be given to women with low serum levels of 25-hydroxyvitamin D (below 50 nmol/L), according to the recommendations from the Institute of Medicine.
1. Michaëlsson K, Melhus H, Warensjö Lemming E, et al. Long-term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study, BMJ. 2013;346:f228.
2. Xiao Q, Murphy RA, Houston DK, et al. Dietary and supplemental calcium intake and cardiovascular diseae mortality: the National Institutes of Health–AARP Diet and Health study. JAMA Intern Med. 2013:1-8. doi:10.1001/jamainternmed.2013.3283.