Vitamin B12 deficiency in diabetic subjects taking metformin: A cross sectional study in a Lebanese cohort

Metformin is the only biguanide derivative used to treat type 2 diabetes mellitus (T2D). Several studies documented that its use contributes to vitamin B12 deficiency in 10–30% of diabetics. The incidence of deficiency varies among populations and studies reported. There has been no reports documenting this incidence in the Middle East and Lebanon.

The objectives of this study were to establish the incidence of vitamin B12 in our population, to investigate and characterize any specific associations between taking metformin and vitamin B12 deficiency to establish clear recommendations based on this data.

During the first 6 months of 2015, we conducted a cross sectional study on 200 Lebanese individuals. The cohort consisted of subjects with an established diagnosis of T2D and who have been on metformin for at least three months. The patients were subjected to a questionnaire, medical record review, and vitamin B12 level measurement.

Thirty three percent of the subjects were found to have borderline values of the serum vitamin B12 (148–220 pg/dl) while 22.5% had a clear, deficiency (levels less than 148 pg/dl). We found a highly significant inverse correlation between the dose and duration of metformin treatment and the serum levels of vitamin B12. Furthermore, both borderline and low levels of vitamin B12 were associated with the presence of different neuropathies and macrocytic anemia in a dose dependent manner.

Based on our results, we strongly recommend the routine screening of subjects with T2D on metformin for vitamin B12 deficiency due to its high prevalence and the significant clinical effects it may result in. Furthermore, we recommend, based on our data, to start treating those subjects once a borderline or low level is detected.