“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
The bone mineral. Large trials have nuanced its promise: it slows bone loss after menopause, but its effect on fractures is much less clear-cut than claimed.
The warning sign to know is cardiac: a meta-analysis of 15 trials (over 8,000 participants) associates calcium taken without vitamin D with an increased risk of myocardial infarction, and a five-year trial in 1,471 healthy postmenopausal women recorded more myocardial infarctions and cardiovascular events on calcium. A systematic review instead judges the cardiovascular effect of calcium alone to be minimal: studies disagree, and if you have a history of heart conditions, speak to your doctor before taking any. Taken with vitamin D, it is accompanied by an increased risk of kidney stones. Constipation is the most frequent adverse effect in the five-year trial. During pregnancy, a small increase in absolute numbers of HELLP syndrome was observed. Finally, the limitations: the evidence that calcium prevents fractures is judged weak and inconsistent, with no effect in the least biased trials; bone density gains are small, do not progress over time, and are unlikely to reduce fractures; and in the five-year trial of 1,460 women over 70, 1,200 mg per day did not reduce fractures in intention-to-treat analysis. It also changes nothing for blood sugar in adults at high risk of diabetes.
Trials test 500 to 1,200 mg of calcium per day; in an older trial, 2,000 mg per day did not prevent bone loss in early menopause. Combined with vitamin D, the 2007 meta-analysis retains at least 1,200 mg of calcium and 800 IU of vitamin D per day. During pregnancy, benefits appear starting from 1 g per day.
Calcium supplements (without associated vitamin D) are associated with an increased risk of myocardial infarction.
This meta-analysis studied the effect of increased calcium intake (dietary or via supplements) on bone mineral density (BMD) in people over 50. Increasing calcium, regardless of its source, produced small, non-progressive increases in BMD. These increases are considered unlikely to clinically reduce fracture risk.
Tai V, Leung W, Grey A, Reid IR, Bolland MJ. — BMJ (Clinical research ed.) (2015) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more