Long-Term Metformin Raises Risk for B₁₂ Deficiency

Metformin — the most commonly prescribed oral drug for patients with type 2 diabetes — induces vitamin B₁₂ malabsorption and therefore can raise risk for vitamin B₁₂ deficiency. In this multicenter randomized trial, Dutch investigators assessed risk for B₁₂ deficiency (blood level, <150 pmol/L), low vitamin B₁₂ level (blood level, 150–220 pmol/L), and elevated blood homocysteine levels in patients with type 2 diabetes who were treated with metformin.

Overall, 390 patients received metformin (850 mg) or placebo three times daily for 4.3 years. Compared with placebo, metformin was associated with a significant 19% decrease in baseline vitamin B₁₂ concentration. The absolute risks for vitamin B₁₂ deficiency and low vitamin B₁₂ level were signif…