Should athletes supplement with antioxidants to protect against exercise-induced oxidative stress?

Should Athletes Supplement with Antioxidants?

No, athletes should not supplement with high-dose antioxidant vitamins (particularly vitamins C and E) to protect against exercise-induced oxidative stress, as these supplements interfere with beneficial training adaptations and may increase mortality risk. 1

Primary Recommendation

The American College of Cardiology and American Heart Association explicitly recommend against prescribing antioxidant vitamins such as vitamin E and/or vitamin C supplements, as they interfere with beneficial cellular signaling pathways (Class III recommendation). 1 Similarly, the UEFA expert statement on elite football nutrition specifically advises against using large doses of individual antioxidant vitamins C and E to reduce exercise-induced inflammation, as this interferes with adaptive processes in muscle. 1

Why High-Dose Antioxidants Are Harmful

Interference with Training Adaptations

• Exercise-generated reactive oxygen species (ROS) serve as essential signaling molecules that drive critical training adaptations, including mitochondrial biogenesis, antioxidant enzyme upregulation, and improved insulin sensitivity. 1
• High-dose antioxidants block these beneficial redox-sensitive signaling pathways, leading to impaired exercise adaptations and blunted training responses. 1, 2
• Athletes taking combined 1000 mg vitamin C plus vitamin E during heavy training periods should discontinue these supplements, as they competitively interfere with skeletal muscle adaptations. 1, 3

Increased Mortality and Disease Risk

• Beta-carotene supplementation at 20-30 mg/day increased lung cancer mortality in two major trials. 1
• Vitamin E supplementation at 400 IU/day increased both prostate cancer risk and heart failure risk. 1
• Systematic reviews conclude that beta-carotene and vitamin E appear to increase mortality, with no evidence supporting their use for primary or secondary prevention. 1
• High-dose antioxidants can paradoxically become pro-oxidants after exerting their antioxidant effect, producing radicals that require other antioxidants for regeneration. 1

The Correct Approach: Food-Based Antioxidants

Athletes should consume 5+ servings of fruits and vegetables daily to obtain antioxidants through whole food sources, which support health, recovery, and performance without interfering with training adaptations. 1

Evidence Supporting Dietary Antioxidants

• Restricting fruit and vegetable intake in athletes resulted in decreased serum carotenoids, increased exercise-associated lipid peroxidation, higher ratings of perceived exertion, and increased inflammatory responses. 1
• Increasing phytonutrient intake substantially increases serum carotenoid concentrations and contributes to enhanced recovery and performance. 1
• Whole foods contain antioxidants in natural ratios and proportions that act synergistically to optimize antioxidant effects without the harmful interference seen with isolated supplements. 4
• Regular consumption of fresh fruits, vegetables, whole grains, legumes, beans, sprouts, and seeds effectively and safely meets all antioxidant requirements in physically active persons. 5

Special Circumstances Requiring Targeted Supplementation

Documented Deficiencies Only

• If vitamin insufficiencies are documented through laboratory testing, correction through diet or targeted supplementation to restore normal physiological levels is appropriate. 1
• Once vitamin levels are replete, high-dose supplementation must be discontinued. 1
• The dose-response relationship is critical: negative effects occur primarily with high-dose supplementation, not physiological amounts from food. 1

Limited Acute Use Scenarios

• Acute administration of 1000 mg ascorbic acid may modestly reduce endotoxin translocation in exercise-associated gastrointestinal symptoms, but this does not justify routine use. 1
• N-acetyl cysteine may provide benefit in the days immediately prior to an endurance event, though this is not a routine recommendation. 3

Common Pitfalls to Avoid

• Do not recommend antioxidant supplements during training blocks focused on adaptation, as this is precisely when ROS signaling is most critical for physiological improvements. 1
• Avoid the misconception that "more is better" with antioxidants—while oxidative stress markers may decrease with supplementation, this does not translate to improved performance and may harm long-term adaptations. 3, 2
• Do not confuse the attenuation of oxidative stress biomarkers with clinical benefit—over 150 studies show supplements reduce oxidative stress markers, but most report no effects on muscle damage or performance, with growing evidence of detrimental effects. 2
• Recognize that ROS are not purely harmful—they are essential signaling molecules for optimal cellular function, vasodilation, and insulin signaling. 2