Metformin increases risk of vitamin B-12 deficiency

As many as 22% of people with type 2 diabetes could have vitamin B-12 deficiency.

This BMJ study evaluated the effects of metformin on the incidence of vitamin B-12 deficiency (lower than 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.

Compared with placebo, metformin treatment was associated with a decrease in vitamin B-12 concentration of -19%.

The absolute risk of vitamin B-12 deficiency (lower than 150 pmol/l) at study end was 7.2 percentage points higher in the metformin group than in the placebo group with a number needed to harm of 13.8 per 4.3 years.

Long term treatment with metformin may increase the risk of vitamin B-12 deficiency, which results in raised homocysteine concentrations. Vitamin B-12 deficiency is preventable; therefore, regular measurement of vitamin B-12 concentrations during long term metformin treatment should be considered.

Image source: Metformin. Wikipedia, public domain.


  1. Hi!

    This is fairly well known, see

    Best wishes


  2. Yes, but restating this type of information via
    Social Media helps to keep the word out there for those who may or may not be aware..

  3. Right. Jon's info is very helpful but the idea is to increase the awareness.

    The info is out there but few practicing physicians and patients are aware of it.