The use of supplemental calcium may have an adverse effect on the cardiovascular health of men but not women, according to a prospective cohort study that was published online Feb. 4 in the Journal of the American Medical Association: Internal Medicine.
The National Institutes of Health (NIH) estimates that about 43 percent of the population in the U.S. consumes dietary supplements that contain calcium, and almost three of every four older women take calcium supplements. While calcium supplements are considered beneficial for preventing and treating osteoporosis, their effect on cardiovascular health is less clear. For instance, one randomized, placebo-controlled trial that enrolled postmenopausal women found that MI was more commonly reported in the group who took calcium supplements (BMJ 2008;336:262-266) while a meta-analysis also found an association between calcium supplements and an increased risk of MI.
Given the inconsistencies in research and the ubiquitous use of supplements, Qian Xiao, PhD, of the cancer epidemiology and genetics division of the National Cancer Institute, and colleagues set out to better understand the relationship between the intake of dietary and supplemental calcium and mortality. They focused their research on total cardiovascular disease (CVD), heart disease and cerebrovascular disease using data from the NIH-AARP Diet and Health Study.
The study population included adults 50 to 71 years old in six states and two metropolitan areas who completed a baseline questionnaire on dietary intake, frequency and dosage of calcium supplements and frequency and dosage of multivitamins in 1995 and 1996. Xiao et al’s study excluded participants with chronic disease whose use of supplements might have been influenced by their conditions, for a final sample of 219,059 men and 169,170 women. The researchers used the Social Security Administration Death Master File and Death Index Plus to tracks deaths.
At a mean 12-year follow-up, they ascertained 7,904 CVD deaths in men and 3,874 CVD deaths in women. They found that overall 23 percent of men and 56 percent of women reported using calcium supplements and 56 percent of men and 58 percent of women took multivitamins containing calcium. The use of calcium intake from supplements or multivitamins was associated with a 20 percent increased risk of CVD death in men as well as an increased risk for heart disease death and cerebrovascular disease death.
The results were null for women, though, and dietary calcium was not associated with an increased mortality risk in either men or women.
The authors called the differences in results for men and women “intriguing.” They cited previous hypotheses that suggested that women are more regular users of calcium supplements and that sudden change in calcium uptake may be a factor in adverse events.
“Although no information on duration of supplement use was collected at baseline in our study, it may be reasonable to assume that, on average, male users started taking calcium supplements at an older age,” they wrote. “Therefore, women were more likely to have achieved calcium balance and stable calcium levels long before the study, and the effect of calcium supplement became less profound.”
They explored the possible mechanistic pathways to adverse events, including vascular calcification, increased blood coagulation and arterial stiffness. Xiao and colleagues emphasized that calcium also may have beneficial effects such as lower blood pressure.
The researchers cautioned that the study lacked data on duration of the use of supplements, change in dietary or supplement usage and family health histories; the data was self-reported; and behaviors related to taking supplements may affect results.
“Given the extensive use of calcium supplement in the population, it is of great importance to assess the effect of supplemental calcium use beyond bone health,” the authors concluded.
In an accompanying editorial, Susanna C. Larsson, PhD, of the Institute of Environmental Medicine at Karolinska Institute in Stockholm, agreed that more large studies are warranted to assess health risks. She advocated eating calcium-rich foods as a safe alternative to supplements.