Vitamin B12 deficiency in long-term metformin use and clinician awareness: a scoping review protocol

A relationship between long-term metformin use and vitamin B12 deficiency has been long discussed in the literature. Nonetheless, prior to 2022, there was no official guidance. In June 2022, the Medicines and Healthcare products Regulatory Agency (MHRA) published advice, stating that low vitamin B12 is now considered to be a common side effect. It advises checking levels in patients with symptoms of B12 deficiency, as well as monitoring those at risk of B12 deficiency.Despite efforts to promote evidence-based practice, there is still a gap in the translation of research findings into policies and clinical practice. The above research has been shared widely in the academic and specialist diabetes literature over a prolonged period. The purpose of the scoping review is to explore what evidence is available regarding clinicians' awareness of the association between metformin use and vitamin B12 deficiency in patients with type 2 diabetes mellitus, how this evidence is implemented into frontline clinical practice and what screening processes are recommended or exist.

This is a protocol for a scoping review to be guided by the Joanna Briggs Institute (JBI) methodology for scoping reviews 20. The databases to be searched will include MEDLINE (accessed via PubMed), British Nursing Index, Google Scholar, Cochrane, Embase, Web of Science and Cumulative Index to Nursing and Allied Health Literature (CINAHL) (accessed via EBSCO), alongside searching for grey literature such as Electronic Theses Online Service (EThOS), DART European and Kings College London Research Portal. Titles and abstracts of articles will be reviewed by the authors. If articles are representative of the inclusion criteria, the articles will go through a full-text review by the authors. The results of the search and study inclusion/exclusion process will be reported and presented in a Preferred Reporting Items for Systematic Reviews and Meta-analyses flow diagram. Data will be extracted from papers, using the recommended JBI data extraction tool. The search will commence in August 2025, and the review is expected to be completed by November 2025.The search will commence in August 2025, and the review is expected to be completed by November 2025.

As this is a scoping review protocol that did not involve any human participants, human data or human tissue, no ethical approval was required. Our dissemination strategy includes peer review publication, presentation at conferences and with relevant stakeholders.