Vitamin B12 deficiency in long-term metformin use and clinician awareness: a scoping review
Abstract
Background: Metformin is the first-line treatment for type 2 diabetes mellitus (T2DM). Long-term use of metformin has been associated with vitamin B12 deficiency, which may lead to serious complications such as anaemia and neuropathy. Although international bodies have recommended screening for vitamin B12 deficiency in patients on long-term metformin, it is unclear how aware clinicians are of this adverse effect and to what extent such guidance is being followed in practice.
Methods: A scoping review was conducted using Joanna Briggs Institute (JBI) methodology. Databases searched included MEDLINE, Medical Literature Analysis and Retrieval System Online (PubMed), British Nursing Index (BNI), Google Scholar, Cochrane, Embase, Web of Science and CINAHL, Cumulative Index to Nursing and Allied Health Literature (EBSCO) alongside searching for grey literature such as EThOS (Electronic Theses Online Service), DART (Digital Access to Research Theses) European and Kings College London Research Portal. Studies published in English from 1990 onwards were included if they addressed clinician awareness or screening practices. Data were extracted and summarised using a structured tool, with themes mapped visually. The literature search was conducted between 1 August 2025 and 1 November 2025 and included studies published from January 1990 onwards.
Results: 23 sources were included in the review. 7 studies directly assessed clinician awareness of metformin-associated vitamin B12…
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