Metabolism Open · Nov 2026
Vitamin B12 Deficiency in Metformin-Treated Adults with Type 2 Diabetes Mellitus in Africa: A Systematic Review and Meta-analysis
By Amare KA, Kahsay NS, Abraha BH et al.
Background Vitamin B12 deficiency is a clinically important complication of long-term metformin therapy and may contribute to hematological and neurological complications in patients with type 2 diabetes mellitus. Although metformin is widely used in Africa, comprehensive evidence on the prevalence and associated factors of vitamin B12 deficiency among metformin-treated patients remains limited and fragmented. This systematic review and meta-analysis aimed to estimate the pooled prevalence of vitamin B12 deficiency and identify factors associated with its occurrence among adults with type 2 diabetes mellitus receiving metformin in Africa. Methods Following PRISMA 2020 guidelines, we searched PubMed, Cochrane Library, AJOL, AIM, DOAJ, ScienceDirect, Google Scholar, and reference lists from January 1, 2000, to October 18, 2026. Eligible studies reported the prevalence of vitamin B12 deficiency in metformin-treated adults with type 2 diabetes mellitus. Methodological quality was assessed using JBI tools, and pooled prevalence was estimated using a random-effects REML model in Stata 17.0. Results Nineteen studies involving 3,108 adults with type 2 diabetes mellitus from 10 African countries were included. The pooled prevalence of vitamin B12 deficiency was 14.7% (95% CI: 9.7–21.6%), with substantial between-study heterogeneity (I² = 94.69%) and a 95% prediction interval of 2.0–59.7%, indicating considerable variation in the expected prevalence across different clinical and population settings. The included studies used heterogeneous study-defined diagnostic criteria and laboratory methods for vitamin B12 deficiency. Therefore, the pooled estimate should be interpreted as a summary of the available African studies rather than as a continent-wide prevalence estimate. Narrative synthesis suggested that older age, longer metformin exposure, and higher metformin doses were the most consistently reported factors associated with vitamin B12 deficiency. Conclusion The available African studies yielded a pooled prevalence of approximately 14.7%, based on study-specific definitions of vitamin B12 deficiency. Vitamin B12 assessment may be particularly relevant in patients receiving long-term or high-dose metformin, especially when neurological or hematological manifestations are present. Systematic review registrations PROSPERO (CRD420261463974).