Vitamin B₁₂ levels in patients with type 2 diabetes mellitus on metformin

Abstract

Background: Due to the clinical benefits of metformin, its associated side effects such as vitamin B₁₂ deficiency are usually overlooked and rarely investigated.

Objective: This study was carried out to determine the serum level of vitamin B₁₂ in Nigerian patients with type 2 diabetes mellitus (T2DM) on metformin.

Methods: Serum vitamin B₁₂ level was determined using high performance liquid chromatography (HPLC) in 81 T2DM patients who have been on metformin for 5 years or more. Vitamin B₁₂ deficiency was defined as serum concentration of <200 pg/dl, borderline deficiency as 200 – 300 pg/dl and >300 pg/dl as normal. Differences in vitamin B₁₂ levels between different groups were assessed using Mann Whitney U test and P<0.05 was considered as statistically significant.

Results: Vitamin B₁₂ deficiency and borderline deficiency were recorded in 8.6% and 26.0% of the patients respectively. Vitamin B₁₂ level was significantly lower in patients who have been on metformin for  ≥10 years compared with patients with <10 years history of metformin use. Similarly, patients who were on metformin at a dose of >1000 mg/day had significantly lower vitamin B₁₂ level when compared with patients on ≤1000 mg/day.

Conclusion: Low serum vitamin B₁₂ level is associated with longer duration and higher dose of metformin use. Therefore, routine determination of vitamin B₁₂ level in patients with T2DM on high dose of metformin and those with prolonged use of metformin might help in identifying patients that would benefit from vitamin B₁₂ supplements.

Keywords: Metformin, Type 2 diabetes mellitus, Vitamin B₁₂ deficiency