In 2010, I wrote about a meta-analysis on calcium supplements and cardiovascular disease, Calcium Supplements: Are They Safe? The association with heart disease was limited to people who started out with a dietary calcium intake of 700 mg/day or more (not including the supplements). Then in 2011, I noted a study on supplement use in older women that found a link between calcium supplements and a lower risk of mortality (Supplement Safety).
Since I recommend that vegans get their calcium levels up to at least 700 mg and preferably the DRI (1,000 mg for adults under 50; 1,200 mg for adults over 50) by whatever means necessary (greens, fortified foods, or supplements), I try to keep track of this research as closely as I can. In February, results from two different studies looking at calcium supplements and cardiovascular disease were reported.
One study was from the USA and followed people aged 50 to 71 at baseline for 12 years (1). No association between cardiovascular disease deaths and calcium intake was found for women. For men, calcium supplements of 400 to 1,000 mg/day was associated with an increased risk of cardiovascular death, but was just barely statistically significant. But supplements of more than 1,000 mg/day were associated with a highly significant increase in cardiovascular mortality:
|< 400||.99 (.94-1.04)|
|> 1,000||1.20 (1.05-1.36)|
When the numbers were stratified for smoking, there was a strong trend towards the risk being mainly in current smokers. The average user of supplements for men had a dietary calcium intake (not including supplements) of 815 mg. So once you figure in another 400 to 1,000+ mg of supplemental calcium, their intakes were anywhere from the DRI to about 50% higher than the DRI.
The second study was from Sweden, on older women (2). All-cause mortality for dietary calcium (not including supplements) was a U-shaped curve, with both low calcium and high calcium associated with an increase in mortality:
|< 600||1.38 (1.27, 1.51)|
|≥ 1,400||1.40 (1.17-1.67)|
The findings were similar, but even stronger for cardiovascular disease, and were also very similar for dietary plus supplemental calcium.
One thing to consider for this Swedish study is that 1,400 mg of non-supplemental calcium would indicate a pretty high dairy intake. If you assume 300 mg per serving of dairy, that’s at least 3 servings of dairy per day (on top of the calcium they might be getting from other foods). The results did not adjust for dairy product intake so it’s possible that dairy of 3 servings (or more) per day could have caused the increase in cardiovascular deaths.
While it’s not yet clear what is going on here, my conclusion remains that vegans should aim for at least 700 to 1,000 mg/d (or 700 to 1,200 mg/d if over 50) from foods or supplements, but that you should not go much above that.
1. Xiao Q, Murphy RA, Houston DK, Harris TB, Chow W, Park Y. Dietary and Supplemental Calcium Intake and Cardiovascular Disease Mortality: The National Institutes of Health–AARP Diet and Health Study. JAMA Intern Med. 2013;():1-8. | link
2. Michaëlsson K, Melhus H, Warensjö Lemming E, Wolk A, Byberg L. Long term
calcium intake and rates of all cause and cardiovascular mortality: community
based prospective longitudinal cohort study. BMJ. 2013 Feb 12;346:f228. | link