Calcium Supplements Can Spell Heart Trouble for Women

A long-term study of Swedish women suggests that consuming more than 1400 mg of calcium per day increases one’s risk of dying, particularly of cardiovascular disease.

Women who take calcium supplements and consume a diet with very high levels of calcium appear to have an increased risk of dying from all causes and particularly from cardiovascular disease and ischemic heart disease, according to the results of a study published on February 13, 2013, in BMJ.

The researchers carried out a longitudinal cohort study on a Swedish mammography cohort established between 1987 and 1990. The study included 61,433 women born between 1914 and 1948 and followed up with them for a median of 19 years. During follow-up, 11,944 (17%) of the participants died, 3862 of cardiovascular disease, 1932 of ischemic heart disease, and 1100 of stroke. The diet of the participants was determined from questionnaires administered at baseline and in 1997 for 38,984 women.

The results found that, compared with those with a calcium intake of 600-1000 mg/day, those with an overall calcium intake of at least 1400 mg/day had significantly higher death rates from all causes (hazard ratio of 1.40), from cardiovascular disease (hazard ratio of 1.49), and of ischemic heart disease (hazard ratio of 2.14). There was, however, no significant difference in rate of death from stroke.

As of 1997, 10,055 (25.8%) of the study population was using some sort of calcium supplementation. The largest source of calcium supplementation was from multivitamins with minerals, which contain 120 mg calcium per tablet and were used by 74% of supplement users. Those who took supplementary calcium had similar levels of overall calcium intake to those who did not use supplementary calcium, and did not have an overall increased risk of death from cardiovascular disease or ischemic heart disease.

However, those who had a high dietary intake of calcium (greater than 1400 mg/day) and took supplementary calcium as well had a higher mortality rate than women with a similarly high intake of calcium but no supplementation. Among calcium tablet users (500 mg calcium per tablet), those with high dietary calcium intake (greater than 1400 mg/day) had a multivariable adjusted hazard ratio of 2.57 for all-cause mortality compared with those who had a dietary calcium intake of 600-999 mg/day. Similar comparisons for those who used any type of calcium supplement and for non-users of calcium supplementation suggested that among women with a high dietary intake of calcium, addition of calcium supplements increased one’s risk of death in a dose-dependent fashion.

The researchers conclude that high intake of calcium in women is associated with increased death rates from all causes and cardiovascular disease, but not from stroke.

“Our present data together with previous observations suggest that for the prevention of fractures in elderly people and simultaneous avoidance of possible serious adverse events related to a high calcium intake (such as higher risk of hip fracture, cardiovascular disease, renal stones, and, as observed in the current study, mortality) emphasis should be placed on people with a low intake of calcium rather than increasing the intake of those already consuming satisfactory amounts,” the researchers write.