Previous studies have revealed that diabetic patients have a decline in immunity and an increased risk of infections, and this may be associated with poor micronutrient status. The aim of this study was to measure the effect of dietary supplements on risk of infection in patients with type 2 diabetes mellitus. One hundred patients with type 2 diabetes mellitus were randomly assigned to receive an oral dose of daily B-group vitamins and antioxidant vitamins (n = 50) or an identical placebo (n = 50) daily for 90 days. Patients had baseline, three and 12 month assessment for nutritional status, fruits and vegetables intake, physical activity and self-reported infections. Supplementation with antioxidants and B-group vitamins significantly increased the plasma concentration of vitamin E and folate and reduced homocysteine in the intervention group (p-values were 0.006, 0.001 and 0.657, respectively). The number of infections reported by the treatment group after three months of supplements was less than that reported by the placebo group, 9 (27%) vs. 15 (36%) (p = 0.623). Corresponding numbers of infections at 12 months were 25 (67.5%) and 27 (56.3%), respectively (p = 0.488). Up to 90% of the diabetic patients were either overweight or obese with a sedentary life style, and their body weight increased further during three months of follow up. The study showed that multivitamin supplements improved vitamin blood concentrations; however, this did not reduce the number of infections in diabetic patients.