Interrelations between metformin administration and vitamin B12 concentrations in a black South African diabetic cohort: a retrospective cohort analysis
Keywords:
metformin, vitamin B12, peripheral neuropathyAbstract
Background: Metformin, widely used in diabetes treatment, is linked to reduced cobalamin (vitamin B12) levels, potentially exacerbating diabetic peripheral neuropathy (PN) and increasing the risk of lower limb amputations. Studies suggest that black individuals might be less prone to vitamin B12 deficiency, but the impact of metformin on vitamin B12 levels in this group is unclear.
Objective: This study investigated the prevalence of vitamin B12 deficiency in diabetics on metformin and examined the relationship between metformin use and PN.
Methods: A retrospective review of patient records from Edendale Hospital’s diabetes clinic in Pietermaritzburg (January 1, 2017, to December 31, 2018) was conducted. Patients over 18 years of black descent with documented vitamin B12 levels were included. The study extracted data on diabetes treatment, vitamin B12 levels, and PN indicators.
Results: Of 668 patients, 558 met the criteria. Metformin was used by 341 patients (61.1%), alone or with other treatments, while 217 (38.9%) did not use metformin. Glycaemic control was similar in both groups (median HbA1C 9.4% (IQR 7.8–11.0) in metformin users vs. 9.46% (IQR 7.1–11.0) in non-users, p = 0.80). Absolute vitamin B12 deficiency was equally rare in both groups (6 [1.8%] in metformin users vs. 4 [1.8%] in non-users, p = 1.0), but metformin users had significantly lower median vitamin B12 levels (299.0 pmol/l vs. 340.0 pmol/l in non-users, p < 0.05). PN prevalence was similar in both groups (31.7% in metformin users vs. 25.1% in non-users, p = 0.12). However, those with borderline-low vitamin B12 levels (≤ 269 pmol/l) had a higher risk of PN (OR 1.6; 95% CI: 1.1–2.3, p = 0.015).
Conclusion: Metformin users showed lower median serum vitamin B12 levels than non-users, with an association between metformin use and borderline-low vitamin B12 levels. Higher metformin doses correlated with lower vitamin B12 levels, yet a direct link between metformin use and PN was not established.
