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Another study reports excess calcium intake can be fatal

Robin Wulffson MD's picture
calcium supplement, cardiovascular disease, heart attack, osteoporosis

Many individuals, particularly seniors, take calcium supplements for bone health. Inasmuch as more women are susceptible to osteoporosis than men, the supplement is more popular among that gender. A new study set out to assess the rate of cardiovascular disease among women who took calcium supplements. Researchers affiliated with Uppsala University (Uppsala, Sweden) and the Karolinska Institutet (Stockholm, Sweden) published their findings on February 13 in the journal BMJ.

In Western nations, significant emphasis has been placed on calcium intake because of its proposed benefit for bone health. Calcium supplementation has become widely used, especially among the senior population. A recent study reported that more than 50% of older men and almost 70% of older women in the US take calcium supplements. The objective of the new study was to investigate the association between long term intake of dietary and supplemental calcium and death from all causes and cardiovascular disease. Tit was designed as a prospective, longitudinal, cohort study, meaning that it comprised a group of women with similar characteristics who were followed continuously for a period of time. The researchers accessed data from the Swedish mammography cohort, a population based cohort established in 1987-1990. The study group comprised 61,433 women (born between 1914 and 1948) who were followed-up for an average 19 years.

The main outcome measures, which were derived from registry data, were time to death from all causes (11,944 women) and cause specific cardiovascular disease (3,862 women), ischemic heart disease (decreased blood flow to the heart; 1,932 women), and stroke (1,100 women). For 88,984 women, diet was assessed by food frequency questionnaires at baseline and in 1997; calcium intake was estimated. Total calcium intake was the sum of dietary and supplemental calcium.

The researcher s found that the risk patterns with dietary calcium intake were non-linear (not increasing in a straight line); the higher risk rates were concentrated around the highest intakes (more than 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 (1.40-fold increased risk), cardiovascular disease (1 49-fold increased risk), and ischemic heart disease (2.14-fold increased risk but not from stroke (0.73). After further analysis, the higher death rate with low dietary calcium intake (less than 600 mg/day) or with low and high total calcium intake was no longer apparent. Use of calcium tablets (6% users; 500 mg calcium per tablet) was not on average associated with all cause or cause specific mortality; however, among calcium tablet users with a dietary calcium intake above 1,400 mg/day the hazard ratio for all cause mortality was 2.57.

The authors concluded that high calcium intake in women is associated with higher death rates from all causes and cardiovascular disease but not from stroke.

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Another study published online on January 4 in the journal JAMA Internal Medicine also reported an increased cardiovascular disease risk with excessive calcium intake; however, it found that the risk was increase only in men, not women. The objective of the study was to investigate whether intake of dietary and supplemental calcium is associated with mortality from total cardiovascular disease, heart disease, and cerebrovascular diseases.

The prospective study was conducted from 1995 through 1996 in California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania; in addition, it included the two metropolitan areas of Atlanta, Georgia, and Detroit, Michigan. The study group comprised 388,229 men and women aged 50 to 71 years from the National Institutes of Health–AARP Diet and Health Study.

Dietary and supplemental calcium intake was assessed at baseline (1995-1996). Supplemental calcium intake included calcium from multivitamins and individual calcium supplements. Cardiovascular disease deaths were determined using the National Death Index. Multivariate Cox proportional hazards regression models adjusted for demographic, lifestyle, and dietary variables were used to estimate relative risks (RRs).

The investigators found that during a mean of 12 years of follow-up, 7,904 cardiovascular disease deaths occurred in men and 3,874 cardiovascular disease deaths occurred in women. 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 cardiovascular death, more specifically with heart disease death but not significantly with cerebrovascular disease death. In women, supplemental calcium intake was not associated with cardiovascular disease death, heart disease death, or cerebrovascular disease death.

The researchers concluded that their findings suggest that high intake of supplemental calcium is associated with an excess risk of cardiovascular disease death in men but not in women. They recommended that additional studies are needed to investigate the effect of supplemental calcium use beyond bone health.

Take home message:
These studies suggest that too much calcium supplementation can impact one’s health. The January study suggests that the health impact from excess calcium has a greater impact on men. Thus, moderation is the key. Inadequate supplementation is not beneficial, adequate supplementation can be beneficial, and excess supplementation can be harmful. Older men are less susceptible to osteoporosis; however, many older men develop osteoporosis.

JAMA Internal Medicine