Strongest evidence: The most researched area is bone mineral density, with 4 studies on increased total hip bone mineral density in postmenopausal women, but the evidence strength is low overall. Two of those studies reported beneficial small-to-moderate effects, but only when calcium was combined with other interventions (exercise or collagen), making it difficult to isolate calcium's role.
Mixed or weaker evidence: For reduced stillbirth in pregnant women (3 studies), the evidence is also low, with 2 studies reporting neutral effects and 1 finding a small benefit that did not reach statistical significance. Similarly, for improved bone mineral density in other populations (3 studies), 1 showed a small benefit in postmenopausal women with osteoporosis, while 2 found neutral effects in kidney transplant recipients and women with type 2 diabetes.
Effective dose patterns: The only specific effective dose reported is 1000 mg/day or greater (calcium carbonate in one study) for stillbirth reduction. No consistent effective dose emerged for bone density outcomes across studies.
Population insights: Postmenopausal women (including those with osteopenia) are the most studied population for bone density outcomes. For stillbirth, research focuses on pregnant women, including those with prior pre-eclampsia/eclampsia. The beneficial effect for bone mineral density was observed only in postmenopausal women with osteoporosis, suggesting the benefit may not generalize to other groups.
Notable caveats: Across all three syntheses, the evidence base is small (3-4 studies each) and generally low in strength. Many individual studies did not reach statistical significance, and beneficial effects were often seen only in combined interventions, not calcium alone. Certainty of evidence ranged from very low to moderate, and outcome measures (e.g., hip vs. femoral neck BMD) were not consistent across studies.