Antioxidant supplementation does not affect fasting plasma glucose in the Supplementation with Antioxidant Vitamins and Minerals (SU.VI.MAX) study in France: association with dietary intake and plasma concentrations.

Background: Observational data suggest a protective effect of several antioxidants on fasting plasma glucose (FPG) and type 2 diabetes. However, randomized trials have yielded inconsistent results.

Objectives: The first objective was to assess the effect of 7.5 y of antioxidant supplementation on FPG at 7.5 y. The second objective was to examine the epidemiologic association of baseline dietary intakes or plasma antioxidants and FPG (at baseline and at 7.5 y).

Design: Subjects (n = 3146) from the Supplementation en Vitamines et Minéraux Antioxydants (SU.VI.MAX) primary prevention trial in France were randomly assigned to receive a daily capsule containing 120 mg vitamin C, 30 mg vitamin E, 6 mg beta-carotene, 100 mug Se, and 20 mg Zn or a placebo.

Results: After 7.5 y, no significant difference was observed between age-adjusted mean FPG in men (P = 0.78) and women (P = 0.89) in either group. Baseline beta-carotene dietary intakes and plasma concentrations were inversely associated with FPG in multivariate mixed models (P = 0.0045 and P < 0.0001, respectively). Baseline plasma vitamin C and selenium were negatively (P = 0.0455) and positively (P < 0.0001) associated, respectively, with FPG.

Conclusions: Supplementation with antioxidants at nutritional doses for 7.5 y had no effect on FPG in men or women who followed a balanced diet. An inverse association of baseline beta-carotene dietary intake and plasma concentrations with FPG was found, probably because beta-carotene is an indirect marker of fruit and vegetable intakes.