According to a new study people with diabetes on metformin should take vitamin B12 more than the recommended daily allowance.

The research, which was published in Diabetes Care, assessed data from the National Health and Nutritional Examination Survey (NHANES) in the United States between 1999 and 2006. The study results showed that the prevalence of biochemical B12 deficiency was greatest for people with type 2 diabetes taking metformin compared with those with type 2 diabetes but not taking metformin and those without diabetes.

B12 deficiency was revealed in 5.8 per cent of patients with diabetes that took metformin as compared to 2.4 per cent of those who did not take metformin and 3.3 per cent of people that did not have diabetes. The study concluded that the amount of B12 recommended by the Institute of Medicine (IOM) (2.4 μg/day) and the amount available in general multivitamins (6 μg) may not be enough to correct this deficiency among those with diabetes.

Researcher Godfrey Oakley commented "It is important to conduct further research to learn how much B12 is needed to correct the deficiency and to determine whether or not raising serum B12 levels improves the clinical picture for persons taking metformin who have low serum B12 concentrations".