Vitamin D recommendations in nutritional guidelines: Protocol for a systematic review, quality evaluation using AGREE-2 and analysis of potential predictors.

BackgroundVitamin 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 and analysisWe searched PubMed, EMBASE and CINAHL databases for vitamin D guidelines for the last 10 years. We aim to perform descriptive analysis, a quality appraisal using AGREE II scores (Appraisal of Guidelines Research and Evaluation) and a bivariate analysis evaluating the association recommendations and AGREE II domains scores and pre-specified characteristics. Ethics and disseminationThis is a systematic review protocol and therefore formal ethical approval is not required, as no primary, identifiable, personal data will be collected. Patients or the public were not involved in the design of our research. However, the findings from this review will be shared with key stakeholders, including patient groups, clinicians and guideline developers. We intend to publish our results in a suitable, peer-reviewed journal.