Assessment of the quality and content of clinical practice guidelines for vitamin D and for immigrants using the AGREE II instrument: global systematic review

Background Worldwide, more immigrants experience vitamin D (vitD) deficiency than non-immigrants. Recommendations in current clinical practice guidelines (CPGs) concerning vitD are inadequate to address vitD deficiency among immigrants, and there are concerns regarding the quality of guidance in these CPGs.Objectives This study aimed to identify and evaluate the quality of published CPGs addressing vitD and immigrants' health using the Appraisal of Guidelines for Research and Evaluation-II (AGREE II) tool and clarify the recommendations pertaining to vitD and immigrant populations in these CPGs.Methods We performed a systematic search to identify the most recent CPGs across various databases (Ovid MEDLINE ALL, Embase and Turning Research Into Practice), guideline repositories and grey literature. Two reviewers independently conducted study selection and data abstraction and evaluated the quality of the included guidelines using the AGREE II tool.Results We identified 25 relevant CPGs; 21 focused on vitD and 4 covered immigrants' health. Around one-quarter of the included CPGs were high quality (>= 60% in at least four of the six domains, including 'rigour of development'). The highest mean scores among the six AGREE II domains were for 'clarity of presentation' and 'scope and purpose'. About 4.8% (1/21) of the CPGs on vitD had immigrant-related recommendations. VitD recommendations were emphasised in one out of the four immigrant health CPGs (25%). CPGs covering immigrants' health and vitD were inadequately systematically appraised. Moreover, recommendations regarding vitD were insufficient to address the growing epidemic of vitD deficiency among immigrant populations.Conclusion The insufficient recommendations for vitD fail to address the rising vitD deficiency among immigrants, highlighting a critical gap in healthcare provisions. Urgent national and international efforts are needed to develop comprehensive CPGs, bridging research, policy and practice disparities. Future guidelines must prioritise routine vitD screening, supplementation protocols for vulnerable immigrant groups, and culturally appropriate interventions to improve health outcomes for immigrants globally.PROSPERO registration number CRD42021240562.