In the multiple linear regression analyses, participants with diabetes taking both metformin and multivitamins showed a significant increase in log serum B12 concentrations (β = 0.407; standard error (SE) = 0.068; P<0.01), compared to those not taking multivitamins, controlling for age, race, sex, geographic region, BMI, smoking, alcohol use and insulin use. This evidence concerns the gene INS and diabetes mellitus.