Calcium

Calcium is the supplement world’s most persistent paradox: it is universally recommended for bone health, yet the largest meta-analysis of its cardiovascular effects found it increases heart attack risk, and the US Preventive Services Task Force concluded there is insufficient evidence to recommend it for routine fracture prevention. Understanding when calcium helps, when it harms, and when it is simply unnecessary requires separating dietary calcium from supplemental calcium — a distinction the marketing almost never makes.

The mechanism is dual. In bone, calcium is the mineral matrix of hydroxyapatite, essential for bone strength and remodeling. In the vasculature, calcium participates in smooth muscle contraction and coagulation activation. Bolland et al. (2010) proposed that acute calcium loading from supplements raises serum calcium transiently, accelerating vascular calcification and increasing coagulability. Dietary calcium, absorbed more slowly and in smaller increments throughout the day, does not produce this acute spike.

The cardiovascular signal is the most contested and important finding. Bolland’s meta-analysis of 15 randomized trials (12,000+ participants) found calcium supplements ≥500mg/day increased myocardial infarction risk by 31% (HR 1.31, 95% CI 1.02-1.67). The number needed to harm was striking: treating 1,000 people for 5 years would prevent 26 fractures but cause 14 additional heart attacks, 10 strokes, and 13 deaths. Critics noted that cardiovascular outcomes were not primary endpoints in the original trials, but the signal has persisted across sensitivity analyses and was biologically plausible.

The fracture-prevention evidence is weaker than commonly assumed. The USPSTF (2018) reviewed the evidence and concluded there is insufficient evidence to recommend routine calcium + vitamin D for primary fracture prevention in community-dwelling postmenopausal women. The 2007 Lancet meta-analysis by Tang et al. found calcium + vitamin D reduced fracture risk only in institutionalized elderly with high adherence; the effect in community-dwelling adults was not significant. Vitamin D alone, weight-bearing exercise, and adequate dietary protein may matter more for bone health than calcium supplements.

The honest framing: prioritize dietary calcium. Dairy, fortified plant milks, leafy greens (kale, collards, bok choy), canned salmon with bones, and tofu made with calcium sulfate all provide calcium in a matrix that does not produce acute serum spikes. If dietary intake is inadequate (<600 mg/day), supplement with the minimum effective dose — 500mg elemental calcium, divided, taken with vitamin D3. Calcium citrate is preferable to carbonate for those with low stomach acid (PPI users, older adults). Consider vitamin K2 (MK-7) to direct calcium toward bone and away from arteries.

Practical guidance: assess dietary intake first. If you consume 2-3 servings of dairy or fortified alternatives daily, you likely do not need supplements. If supplementing, 500mg elemental calcium daily, divided, with meals (carbonate) or anytime (citrate). Recheck need periodically — calcium is not a “take forever” supplement. Those with kidney stones, hyperparathyroidism, or sarcoidosis should avoid supplements entirely.