Vitamin B12 deficiency and the lack of its consequences in type 2 diabetes patients using metformin

Objectives: To study vitamin B-12 concentrations in patients with type 2 diabetes with and without metformin use and to identify risk factors and consequences of low vitamin B-12 concentrations. Research design and methods: This study had a cross-sectional design. During eight weeks all patients with type 2 diabetes visiting the diabetic outpatient clinic of the Isala Clinics in Zwolle were approached for participation. Participation included measurement of haemoglobin, mean corpuscular volume and vitamin B-12 levels. Data on neuropathy were retrospectively searched for in the patient records. Vitamin B-12 deficiency was defined as serum B-12 concentrations <150 pmol/l. Results: In the total cohort (n=298), the overall prevalence of vitamin B-12 concentrations <150 pml/l was 9.7% (95% CI 6.6-13.7%). In type 2 diabetes patients not taking metformin (n=134), the prevalence was 4.4% (95% CI 1.6-9.4%) compared with 14.1% in metformin users (n=164) (95% CI 9.2-20.4%; p=0.006). Each 100 mg step in metformin dose increased (OR=1.081, p=0.014), whereas PPI use lowered (OR=0.322, p=0.037) the odds of having a vitamin B-12 deficiency in logistic regression. Nevertheless, metformin use did not predict the chance on having anaemia or neuropathy. Conclusion: Among patients with type 2 diabetes using metformin, the prevalence of vitamin B-12 deficiency is higher than compared with patients not using metformin. However, metformin use did not predict the chance of having anaemia or neuropathy.