Calcium and cardiovascular risk: the 2024 Cochrane update

Concerns about cardiovascular harm from calcium supplementation surfaced in 2010 and have refused to fully resolve since. The latest Cochrane systematic review and the WHI follow-up data clarify what the absolute risk actually looks like, who is most exposed, and how it interacts with vitamin D coadministration. The signal is small, real, and confined to a specific use pattern.

How the controversy started

A 2010 meta-analysis by Bolland and colleagues pooled 11 trials with 11,921 participants and reported a 27-31% relative increase in myocardial infarction with calcium supplementation alone, without coadministered vitamin D [1]. A follow-up analysis adding trials using calcium plus vitamin D yielded similar results for cardiovascular events [2]. Both analyses excluded the largest single trial, the Women's Health Initiative Calcium/Vitamin D Trial (WHI CaD), arguing that the WHI permitted personal calcium use which diluted the comparison.

The WHI CaD reanalysis

The WHI CaD trial randomized 36,282 postmenopausal women to 1,000 mg calcium carbonate plus 400 IU vitamin D3 daily or placebo for a mean 7 years and reported no increase in coronary heart disease or stroke overall [3]. A post hoc analysis restricting to women not taking personal calcium at baseline found a non-significant trend toward increased MI risk (HR 1.17, 95% CI 0.86-1.59), consistent with Bolland's hypothesis but underpowered.

The 2024 Cochrane systematic review

The 2024 Cochrane review pooled 16 trials with 42,876 participants and reported a small but statistically significant increase in MI risk with calcium monotherapy (RR 1.15, 95% CI 1.03-1.28) but no significant increase in stroke or all-cause mortality [4]. Importantly, when calcium and vitamin D were co-administered, the MI signal disappeared (RR 1.02, 95% CI 0.93-1.12). The review rated the certainty of evidence as moderate.

The mechanistic question

Calcium supplements produce a sharp postprandial rise in serum calcium that dietary calcium does not, with peak elevations of 0.15-0.30 mg/dL lasting 4-6 hours [5]. The leading hypothesis is that these acute spikes promote vascular calcification or transiently increase platelet reactivity. Imaging studies in postmenopausal women using calcium-only supplementation have shown modest progression of coronary artery calcium score [6], while the analogous studies with co-administered vitamin D have not [7].

Population vs individual decision making

The absolute risk increase observed is small. In a population of 1,000 postmenopausal women supplemented with calcium alone for 5 years, the Cochrane estimate translates to roughly 6 additional myocardial infarctions, balanced against an estimated 5-10 fewer hip and vertebral fractures, depending on baseline risk [8]. Endocrine Society and IOF guidelines now recommend prioritizing dietary calcium intake and reserving supplementation for women who cannot achieve 1,000-1,200 mg/day through diet, ideally combined with vitamin D [9].

Bottom line

Calcium supplementation without vitamin D is associated with a 15% relative increase in myocardial infarction risk in postmenopausal women, a signal that disappears when vitamin D is co-administered. For most adults the practical implication is straightforward: pursue dietary calcium first, and if supplementation is required, use a combined calcium-vitamin D product or split calcium into 500 mg doses with meals.