Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial.

Objectives: To study the effects of metformin on the incidence of vitamin B-12 deficiency (<150 pmol/l), low concentrations of vitamin B-12 (150-220 pmol/l), and folate and homocysteine concentrations in patients with type 2 diabetes receiving treatment with insulin.

Design: Multicentre randomised placebo controlled trial.

Setting: Outpatient clinics of three non-academic hospitals in the Netherlands.