Prevalence of vitamin B 12 deficiency among metformin-treated type 2 diabetic patients in a tertiary institution, South-South Nigeria

Background: The risk of chronic metformin pharmacotherapy to cause vitamin B 12 deficiency and its associated medical complications has been of immense concern among diabetic patients. Some studies have postulated that vitamin B 12 deficiency is highly prevalent among chronic metformin-treated adult diabetic patients.Aim: This study aimed to determine the prevalence of vitamin B 12 deficiency among metformin-treated and metformin-naïve type 2 diabetes mellitus patients.Materials and methods: This was a case-control, prospective, analytical, observational study of 200 adult participants (100 per group) attending the Endocrinology, Medical Out-patients Clinic of Irrua Specialist Teaching Hospital, Irrua, Edo State, Nigeria. The participants’ serum vitamin B 12 levels were determined using an immunoassay technique. Data were presented using tables and charts. Chi-square test was used to compare non-continuous proportional variables.Results: The prevalence of vitamin B 12 deficiency was 41% and 20% among metformin-treated and metformin-naïve type 2 diabetes mellitus groups, respectively (p = 0.001). Borderline vitamin B 12 status was present among 59% of metformin-treated group and 80% of metformin-naïve group (p = 0.001). Neither metformin-treated nor metformin-naïve groups had normal serum vitamin B 12 levels.Conclusion: The prevalence of vitamin B 12 deficiency was significantly high in diabetics, especially the metformin-treated patients. We advocate for vitamin B 12 supplementation among this group of patients in order to prevent the occurrence of vitamin B 12 deficiency complications such as macro-ovalocytic anemia, impaired immunity with hypersegmented neutrophils, peripheral neuropathy and subacute degeneration of the spinal cord.