Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 21325105 · doi:10.1152/ajpendo.00207.2010
What was done
Twenty-one young healthy men (mean age 29 ± 1 years, BMI 25 ± 3 kg/m²) were randomized to receive either daily antioxidant supplementation (500 mg vitamin C and 400 IU vitamin E [α-tocopherol]) or placebo while undergoing a 12-week supervised intense endurance-training program (5 times/week). A 3-hour euglycemic-hyperinsulinemic clamp, maximal oxygen consumption (VO2max) and maximal power output (Pmax) testing, body composition assessments, and muscle biopsies were performed before and after the intervention.
What was found
Plasma levels of vitamin C (P < 0.05) and α-tocopherol (P < 0.05) increased markedly in the antioxidant group. Insulin-stimulated glucose uptake increased similarly after training in both the antioxidant group (17.2%, P < 0.05) and the placebo group (18.9%, P < 0.05). VO2max and Pmax also increased similarly in both groups (time effect, P < 0.0001 for both), as did protein content of GLUT4, hexokinase II, and total Akt (time effect, P ≤ 0.05 for all).
Why it matters
These findings demonstrate that combined vitamin C and E supplementation does not impair endurance exercise-induced improvements in insulin sensitivity or muscular glucose-handling proteins in healthy young men.
Limits
The sample size was small (n = 21) and limited strictly to young, healthy men, precluding conclusions about females, older populations, or individuals with impaired glucose tolerance. Only a single combination and dose of antioxidants was tested.
Cited by
- context High-dose alpha-tocopherol and vitamin C supplementation suppress the insulin sensitivity benefits of exercise.