Vitamin D has been widely promoted for bone health through supplementation and fortification of the general population. However, there is growing evidence that does not support these strategies. Our aim is to review the quality and recommendations on vitamin D nutritional and clinical practice guidelines and explore predictive factors for their direction and strength. Methods We searched Medline, TRIP, G-I-N and guidelines.gov databases for guidelines from January 2010 to January 2018. We

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... med a descriptive analysis, a quality appraisal using AGREE II scores (Appraisal of Guidelines Research and Evaluation) and a bivariate analysis evaluating the association between direction and strength of recommendations, three AGREE II domains' scores (Rigor of development, Applicability and Editorial Independence) and pre-specified characteristics. Results We included 24 guidelines in our review. Nine recommended supplementation, eight suggested its use, and seven did not recommend it. The mean score for "Rigor of development" domain was 40.1%. For the "Applicability" domain 34.5% and 39.6% for "Editorial independence" domain. The majority of guidelines did not reach and overall of 60% on these independent scores to be considered high quality. Guidelines with higher scores in these domains were less likely to recommend or suggest vitamin D supplementation (64% recommending against vs 29% suggesting for, and 27% recommending for; p=0.002, 52% vs 26% and 25%; p=0.003, 61% vs 35% and 24%; p=0.001, respectively). Guidelines with potential conflicts of interest were more likely to recommend or suggest vitamin D supplementation (likelihood ratio: p=0.018). Conclusions Policymakers, clinicians and patients should be aware that lower quality guidelines, and those reporting conflicts of interest are more likely to promote vitamin D supplementation. Guideline organizations should improve the quality of their recommendations' development and the management of conflicts of interest. Users and