NMA: Nonprescription Medicines Academy

Calcium Supplements: Too Much of a Good Thing?

April 17th, 2013

Recently reported results from two studies link high intake of supplemental calcium with an increased risk of cardiovascular (CVD) death.

National Institutes of Health–AARP Diet and Health Study
Among participants in the National Institutes of Health (NIH)–AARP Diet and Health Study, high intake of supplemental calcium was associated with an excess risk of cardiovascular (CVD) death in men but not in women.

The prospective NIH–AARP Diet and Health Study included 388,229 men and women 50 to 71 years of age from California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania, as well as the two metropolitan areas of Atlanta, Georgia, and Detroit, Michigan. Dietary and supplemental calcium intake was assessed at baseline (1995-1996); supplemental calcium intake reflected calcium from multivitamins as well as individual calcium supplements. Cardiovascular disease deaths were verified using the National Death Index.

During a mean of 12 years of follow-up, there were 7,904 deaths in men and 3,874 deaths in women attributed to CVD. Supplements containing calcium were used by 51% of men and 70% of women. In men, supplemental calcium intake was associated with an elevated risk of CVD death (RR>1000 vs 0 mg/day, 1.20; 95% CI, 1.05–1.36) and heart disease death (RR, 1.19; 95% CI, 1.03–1.37) but not cerebrovascular disease death (RR, 1.14; 95% CI, 0.81–1.61). In women, supplemental calcium intake was not associated with CVD death (RR, 1.06; 95% CI, 0.96–1.18), heart disease death (1.05; 0.93–1.18), or cerebrovascular disease death (1.08; 0.87–1.33). Dietary calcium intake was unrelated to CVD death in either men or women.

The authors concluded that additional studies are needed to investigate the effect of supplemental calcium use beyond bone health. (JAMA Intern Med. 2013 Feb 4:1-8. [Epub ahead of print])

Swedish Mammography Cohort
In the Swedish mammography cohort—a population-based cohort of 61,433 women in two Swedish counties (Uppsala and Västmanland) born between 1914 and 1948—high intakes of calcium were associated with higher death rates from all causes and cardiovascular disease, but not from stroke.

The Swedish mammography cohort was established in 1987-90. Participants completed a questionnaire at baseline covering diet (food frequency questionnaire) and lifestyle; a second, expanded questionnaire was distributed in 1997 to women still living in the study area (responses received from 38,984 women). Intakes of calcium were estimated from these questionnaires, with total calcium intake reflecting the sum of dietary and supplemental calcium. Primary outcome measures, identified from the Swedish cause of death registry, were time to death from all causes (n = 11,944) and cause-specific cardiovascular disease (n = 3,862), ischemic heart disease (n = 1,932), and stroke (n = 1,100).

Over a median follow-up period of 19 years (the study concluded in December 2008), the risk patterns with dietary calcium intake were nonlinear, with higher rates concentrated around the highest intakes (≥1,400 mg/day). Compared with intakes between 600 and 1,000 mg/day, intakes above 1,400 mg/day were associated with higher death rates from all causes (hazard ratio [HR], 1.40; 95% CI, 1.17–1.67), cardiovascular disease (HR 1.49; 95% CI, 1.09–2.02), and ischemic heart disease (HR 2.14; 95% CI, 1.48–3.09) but not from stroke (HR 0.73; 95% CI, 0.3–1.65).

Use of calcium supplements (500 mg calcium per tablet; used by 6% of cohort) was not on average associated with all-cause or cause-specific mortality. However, the combination of a high dietary calcium intake and use of calcium supplements resulted in a more pronounced increase in mortality. Among supplement users with a dietary calcium intake >1,400 mg/day, the HR for all-cause mortality was 2.57 (95% CI, 1.19–5.55). (BMJ. 2013 Feb 12;346:f228.)