Aims/hypothesis  

Type 2 diabetes is associated with reduced antioxidant defence. Only a few human studies have investigated the role of antioxidants in the pathogenesis of diabetes. This study aimed to examine whether α-tocopherol or β-carotene affected the occurrence of type 2 diabetes.

Methods  

In the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, a double-blind, controlled trial, 29,133 male smokers aged 50–69 years were randomised to receive either α-tocopherol (50 mg/day) or β-carotene (20 mg/day) or both agents or placebo daily for 5–8 years (median 6.1 years). Baseline serum samples were analysed for α-tocopherol and β-carotene using HPLC. Cases of diabetes were identified from a nationwide Finnish registry of patients receiving drug reimbursement for diabetes. Of 27,379 men without diabetes at baseline, 705 men were diagnosed with diabetes during the follow-up of up to 12.5 years.

Results  

Baseline serum levels of α-tocopherol and β-carotene were not associated with the risk of diabetes in the placebo group: the relative risk (RR) between the highest and lowest quintiles of α-tocopherol was 1.59 (95% CI 0.89–2.84) and that for β-carotene was 0.66 (95% CI 0.40–1.10). Neither supplementation significantly affected the incidence of diabetes: the RR was 0.92 (95% CI 0.79–1.07) for participants receiving α-tocopherol compared with non-recipients and 0.99 (95% CI 0.85–1.15) for participants receiving β-carotene compared with non-recipients.

Conclusions/interpretation  

Neither α-tocopherol nor β-carotene supplementation prevented type 2 diabetes in male smokers. Serum levels of α-tocopherol and β-carotene were not associated with the risk of type 2 diabetes.