BACKGROUND: The growing number of systematic reviews/meta-analyses (SR/MAs) on the role of vitamin D in fracture prevention has led to conflicting results and contradictory guidelines. METHODS: This umbrella review evaluated SR/MAs of randomized controlled trials that compare the effect of vitamin D (±calcium) to placebo/control on fracture risk in adults, as identified from 4 databases (2010-2020). We assessed the quality of SR/MAs using the latest quality tool, AMSTAR-2. We compared their results and investigated reasons for discordance using matrices and sub-group analyses (PROSPERO registration: CRD42019129540). FINDINGS: We included 25 SR/MAs, 21 were of critically low quality, one of low quality, and three were of moderate quality (2 were on fall-related fracture). Vitamin D combined with calcium (Ca/D) reduced the risk of hip fractures in 8/12 SR/MAs (relative risk (RR) 0.61-0.84), and the risk of any fracture in 7/11 SR/MAs (RR 0.74-0.95), on pooled analyses. Important sources of discordance in results between SR/MAs were identified. These stem from inclusion of different trials, search periods, eligibility criteria, and differences in methodology. There was a trend for sub-group effect by residency, age and vitamin D status, but none reached statistical significance. All 19 SR/MAs on vitamin D alone compared to placebo/control reported no benefit. INTERPRETATION: Ca/D reduces the risk of hip and any fractures, results that seem driven by findings in institutionalized subjects. Age and baseline vitamin D status may be important predictors. Individual participant data meta-analyses of older patients on Ca/D would best unravel determinants for a beneficial response to such supplementation. FUNDING STATEMENT: This study was in part supported by internal institutional funds from the Medical Practice Plan, at the American University of Beirut Medical Center. DECLARATION OF INTERESTS: Drs M. Chakhtoura, D. Bacha, C. Gharios, Y. Jabbour, F. Kahale, A. Bassatne, S. Antoun, E. Akl and G. El Hajj Fuleihan, and Ms S. Ajjour and M. Assaad have no conflict of interest Dr. P. Ebeling reports grants and other from Amgen, grants from Eli-Lilly, grants from Alexion, other from Sanofi, outside the submitted work. Dr. R. Bouillon reports receiving small lecture fees from FAES (Spain), Proctor &Gamble (Belgium), Abiogen (Italy), and support for attending meetings and/or travel from FAES (Spain), Abiogen (Italy). Dr P. Lips reports receiving travel cost for vitamin D workshop from Abiogen.