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CALCIUM SUPPLEMENTS AND MORTALITY

When the National Institutes of Health – AARP Diet and Health Study reported that men who took calcium supplements had a higher risk of dying from cardiovascular disease compared those who didn't (ref 1) it was the 3rd large cohort in 6 months with alarming findings regarding calcium supplements. The Swedish Mammography cohort that said women who take calcium supplements have a higher risk of mortality from (ref 2) and the Heidelberg cohort (ref 3) found calcium supplements increased the risk of CVD in both sexes.

The National Institutes of Health-AARP Diet and Health Study
The National Institutes of Health-AARP Diet and Health Study followed almost 220,000 men and 170,000 women aged 50 - 70 from 1995/1996 until 2007/2008. The study was set up to investigate cancer as it relates to diet and other factors. Calcium supplements were used by half of the men and over 2/3 of the women. In men, supplemental calcium (from multi's and/or calcium) intake over 1000 mg/d was associated with an elevated risk of death from cardiovascular disease, specifically myocardial infarction. What didn't make headlines was that all-source calcium up to 1200 mg/d actually reduced mortality rates.

Swedish Mammography Cohort
Swedish Mammography Cohort was done between 1987 & 1990.
90,000 women (ages 39-73) were offered a free mammography screening if they filled out questionnaires on diet and lifestyle. 74% responded and 92% (61,433) met the inclusion requirements. In 1997 ~56,000 still living locally were contacted and ~70% replied. 99% (38,894) were included (they had previously met inclusion requirements) and answered a longer questionnaire. The headlines that made the news were:

-- High calcium intake (>1400 mg/day) was associated with an increased rate of mortality, including death from cardiovascular disease & heart disease.
--The increase was moderate when high calcium intake was from food only.
--The risk became significant when high calcium was from a combination of dietary calcium and supplemental calcium.
--Women who got less than 1400 mg/d of calcium from diet and supplements had “modest differences in risk” compared to women who got the same amount of calcium from diet only.
-- Dietary calcium below 600 mg/d had a mortality rate that was similar to subjects who consumed over 1400 mg/d.
What didn't make the headlines was the actual conclusion:
" 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."
In other words, only the women who got more than enough calcium from their diet and then took calcium supplements elevated their risk of mortality.

The Heidelberg Cohort of the European Prospective Investigation into Cancer and Nutrition

The Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition study was the first of 3 large anti-calcium supplement papers published. 23980 subjects aged 35–64 years and free of major CVD events at recruitment, were followed for an average of 11 years. The investigators found that calcium from supplements - but not dietary calcium (either dairy or non-dairy) - increased the risk for MI. When other supplements were taken with the calcium, the risk was less pronounced. The authors did not get any information on what “other supplements” were. There were other problems with the study that the popular press overlooked. They are best described by the authors themselves (ref 3):
"...we therefore only identified a limited number of calcium supplement users, who accounted for 3.6% of all cohort participants..."
"...this model was based on a hypothetical linear relationship between times of self-reported calcium supplementation and MI risk."
"...one single measure of dietary nutrient intakes at baseline apparently could not capture the long-term variation, as we know that individuals might modify their diet.."

COMMENT
Analyzing or re-analyzing complex statistical data from large observational studies is no easy task. Trust me, my eyes became blurry pouring over the statistics from these 3 studies. Often, a headline or sound bite can often be misleading or even incorrect. That is not to say we should ignore the results of these cohorts, because we shouldn't. And if supplemental calcium is actually unhealthy, we want to know it. But, we must also take the time to understand what was actually observed and analyzed and how the numbers were calculated before coming to a conclusion. All 3 of these studies generated news that made a confused public even more confused about what’s good and what’s bad.

In my previous article on the most common mistakes people make when taking dietary supplements (see DC _________) taking any dietary supplement when there is no dietary deficiency is unnecessary,* a waste of money, could be unhealthy and is a very common error many people make because they ‘take them without knowing if they need them.’ It appears that this is exactly what the authors of these studies observed. Unfortunately, it was not presented this way to the public.

*Unless prescribed by a healthcare professional to treat a specific problem or condition.
1. Xiao Q, Murphy RA, Houston DK, et al. Dietary and Supplemental Calcium Intake and Cardiovascular Disease Mortality: The National Institutes of Health-AARP Diet and Health Study.JAMA 2013; Feb 4:1-8.

2. Michaëlsson, K Melhus, H et al. Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study BMJ 2013;346:f228

3 Li,K Kaaks, R Linseisen, J Rohrmann S. Associations of Dietary Calcium Intake and Calcium Supplementation With Myocardial Infarction and Stroke Risk and Overall Cardiovascular Mortality in the Heidelberg Cohort of the European Prospective Investigation Into Cancer and Nutrition Study Heart. 2012;98(12):920-925.

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