Association of Biochemical B12 Deficiency With Metformin Therapy and Vitamin B12 Supplements.

OBJECTIVE--To describe the prevalence of biochemical B₁₂ deficiency in adults with type 2 diabetes taking metformin compared with those not taking metformin and those without diabetes, and explore whether this relationship is modified by vitamin B₁₂ supplements. RESEARCH DESIGN AND METHODS--Analysis of data on U.S. adults ≥50 years of age with (n = 1,621) or without type 2 diabetes (n = 6,867) from the National Health and Nutrition Examination Survey (NHANES), 1999-2006. Type 2 diabetes was defined as clinical diagnosis after age 30 without initiation of insulin therapy within 1 year. Those with diabetes were classified according to their current metformin use. Biochemical B₁₂ deficiency was defined as serum B₁₂ concentrations ≤148 pmol/L and borderline deficiency was defined as >148 to ≤221 pmol/L. RESULTS--Biochemical B₁₂ deficiency was present in 5.8% of those with diabetes using metformin compared with 2.4% of those not using metformin (P = 0.0026) and 3.3% of those without diabetes (P = 0.0002). Among those with diabetes, metformin use was associated with biochemical B₁₂ deficiency (adjusted odds ratio 2.92; 95% CI 1.26-6.78). Consumption of any supplement containing B₁₂ was not associated with a reduction in the prevalence of biochemical B₁₂ deficiency among those with diabetes, whereas consumption of any supplement containing B₁₂ was associated with a two-thirds reduction among those without diabetes. CONCLUSIONS--Metformin therapy is associated with a higher prevalence of biochemical B₁₂ deficiency. 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. [ABSTRACT FROM AUTHOR]