Antioxidants prevent health-promoting effects of physical exercise in humans

Abstract

Exercise promotes longevity and ameliorates type 2 diabetes mellitus and insulin resistance. However, exercise also increases mitochondrial formation of presumably harmful reactive oxygen species (ROS). Antioxidants are widely used as supplements but whether they affect the health-promoting effects of exercise is unknown. We evaluated the effects of a combination of vitamin C (1000 mg/day) and vitamin E (400 IU/day) on insulin sensitivity as measured by glucose infusion rates (GIR) during a hyperinsulinemic, euglycemic clamp in previously untrained (n = 19) and pretrained (n = 20) healthy young men. Before and after a 4 week intervention of physical exercise, GIR was determined, and muscle biopsies for gene expression analyses as well as plasma samples were obtained to compare changes over baseline and potential influences of vitamins on exercise effects. Exercise increased parameters of insulin sensitivity (GIR and plasma adiponectin) only in the absence of antioxidants in both previously untrained (P < 0.001) and pretrained (P < 0.001) individuals. This was paralleled by increased expression of ROS-sensitive transcriptional regulators of insulin sensitivity and ROS defense capacity, peroxisome-proliferator-activated receptor gamma (PPARgamma), and PPARgamma coactivators PGC1alpha and PGC1beta only in the absence of antioxidants (P < 0.001 for all). Molecular mediators of endogenous ROS defense (superoxide dismutases 1 and 2; glutathione peroxidase) were also induced by exercise, and this effect too was blocked by antioxidant supplementation. Consistent with the concept of mitohormesis, exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.

Trial registration: ClinicalTrials.gov NCT00638560.

Fig. 1.

Antioxidants prevent exercise-dependent induction of insulin sensitivity. (A) Glucose infusion rates (GIR) during euglycemic hyperinsulinemic clamps in previously untrained individuals before (white bars) and after (shaded bars) physical exercise over 4 weeks. (Left pair of bars) Individuals not taking any medication or placebo; (Right pair of bars) individuals taking both vitamin C (1000 mg/day) as well as vitamin E (400 IU/day). Bars depict means, error bars show standard error means (applies to all subsequent panels and figures). Significances (applies to all subsequent panels and Fig. 3): * indicates 0.01 < P < 0.05 comparing data before and after 4 weeks of exercise, # indicates 0.01 < P < 0.05 comparing “no suppl.” with “Vit.C/Vit.E” groups after intervention, ** indicates 0.001 ≤ P ≤ 0.01 comparing data before and after 4 weeks of exercise, ## indicates 0.001 ≤ P ≤ 0.01 comparing “no suppl.” with “Vit.C/Vit.E” groups after intervention, *** indicates P < 0.001 comparing data before and after 4 weeks of exercise, ### indicates P < 0.001 comparing “no suppl.” with “Vit.C/Vit.E” groups after intervention. (B) The same set of data derived from a physically pretrained group of individuals. (C) Plasma adiponectin levels in the previously untrained and previously trained (D) state.

Fig. 2.

Antioxidants prevent induction of molecular mediators of insulin sensitivity and antioxidant defense in exercised skeletal muscle. (A) depicts expression levels of PGC1α RNA transcripts in skeletal muscle biopsies derived from previously untrained individuals before (white bars) and after (shaded bars) physical exercise over 4 weeks as described in the Methods section. (Left pair of bars) Individuals not taking any medication or placebo; (Right pair of bars) individuals taking both vitamin C (1000 mg/day) as well as vitamin E (400 IU/day). Bars depict means, error bars show standard error means, “AU” abbreviates normalized arbitrary units. (B) depicts expression levels of PGC1α RNA transcripts in skeletal muscle biopsies derived from pretrained individuals before (white bars) and after (shaded bars) physical exercise over 4 weeks. (C and D) expression levels of PGC1β RNA transcripts in a similar fashion; (E and F) expression levels of PPARγ RNA; (G and H) levels of superoxide dismutase 1 (SOD1) RNA expression; (I and J) RNA levels of superoxide dismutase 2 (SOD2); (K and L) glutathione peroxidase 1 (GPx1) RNA expression levels.

Fig. 3.

Mitohormesis links physical exercise and subsequent formation of reactive oxygen species to insulin sensitivity and antioxidant defense. Physical exercise exerts ameliorating effects on insulin resistance by increasing mitochondrial formation of reactive oxygen species in skeletal muscle to induce expression of PGC1α, PGC1β, and PPARγ as inducers of insulin sensitivity, as well as superoxide dismutases 1 and 2 and glutathione peroxidase 1, key enzymes of ROS defense. Notably, by blocking exercise-dependent formation of reactive oxygen species due to ingestion of antioxidant supplements, health promoting effects of physical exercise are abolished, and physical exercise fails to promote insulin sensitivity and antioxidant defense in the presence of vitamin C and vitamin E.