More evidence supports restraint with calcium supplementation

An extensive study just published in BMJ (British Medical Journal) offers more evidence* that higher levels of calcium intake can increase the risk of death from cardiovascular disease, ischemic heart disease and all causes. This is a particularly important public health issue because 60% of middle-age and older women in the U.S. regularly take calcium supplements despite earlier studies that suggest caution. The authors state:

"We hypothesised that long term intake of low or high calcium increases the risk of cardiovascular mortality. We investigated associations between long term dietary and supplemental intake of calcium with all cause mortality as well as with cardiovascular mortality in a large population based prospective study of Swedish women."

They examined 19 years' worth of data on 61,433 women included in the Swedish mammography cohort, using time to death from all causes and as well as cardiovascular disease, ischaemic heart disease, and stroke as their main outcome measures. Total calcium intake included both dietary and supplemental calcium. Their data revealed a definite association:

"The risk patterns with dietary calcium intake were non-linear, with higher rates concentrated around the highest intakes (≥1400 mg/day). Compared with intakes between 600 and 1000 mg/day, intakes above 1400 mg/day were associated with higher death rates from all causes (hazard ratio 1.40), cardiovascular disease (1 49), and ischaemic heart disease (2.14) but not from stroke (0.73). After sensitivity analysis including marginal structural models, the higher death rate with low dietary calcium intake (<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 but among calcium tablet users with a dietary calcium intake above 1400 mg/day the hazard ratio for all cause mortality was 2.57."

That's a 257% increase in the risk of death when calcium supplements were combined with a high dietary intake.

"Women who had a high dietary intake of calcium exceeding 1400 mg/day and additionally used calcium supplements had a higher mortality rate than women with a similarly high intake of calcium but without taking supplements...Thus, among women with a high dietary intake of calcium, the addition of calcium supplements increased the risk of death in a dose dependent fashion."

One size does not fit all for calcium or anything else. Factors including total dietary intake of calcium plus magnesium status and biomarkers of inflammation should be examined by clinicians before recommending calcium supplements. How might calcium supplementation result in the up-regulation of inflammatory pathways? One mechanism for which there is evidence is by opposing the assimilation and activity of magnesium which has anti-inflammatory properties*. In conclusion:

"In this study of women in the Swedish mammography cohort, a high calcium intake (>1400 mg/day) was associated with an increased rate of mortality, including death from cardiovascular disease. The increase was moderate with a high dietary calcium intake without supplement use, but the combination of a high dietary calcium intake and calcium tablet use resulted in a more pronounced increase in mortality. For most women with lower intakes we observed only modest differences in risk."

* See earlier posts on this topic by searching 'calcium' and 'magnesium' in the search box above.