The Role of Calcium Supplementation on Bone Mineral Density and Fracture Risk in Adults: An Umbrella Review.

We aimed to evaluate the impact of calcium supplementation on bone mineral density (BMD), osteoporosis, and site-specific fracture risk in adults. We conducted a systematic search of MEDLINE, EMBASE, Web of Science, the Cochrane Database of Systematic Reviews (CDSR), and CINAHL from inception to February 13, 2025, to identify systematic reviews with meta-analyses assessing calcium supplementation and fracture or osteoporosis outcomes in adults (≥18 years). Primary-study data from eligible meta-analyses were extracted to assess pooled estimates. Certainty of evidence was assessed using the GRADE framework. Twenty-two meta-analyses were included, comprising 69 unique primary studies and 286,584 participants. Calcium supplementation, with or without vitamin D, was associated with small but statistically significant increases in BMD at the total body, hip, lumbar spine, and femoral neck, although heterogeneity was substantial. Calcium supplementation was associated with reduced risk of total, vertebral, and non-vertebral fractures, but not hip or wrist fractures. Subgroup analyses by intervention type, sex, and age showed no consistent differential effects. Certainty of evidence ranged from moderate for vertebral and non-vertebral fractures to low or very low for other outcomes. Overall, calcium supplementation confers modest skeletal benefits. Further high-quality long-term trials are still needed. (PROSPERO Registration Number: CRD420251082510).