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

Should Athletes Supplement with Antioxidants?

Athletes should NOT supplement with high-dose isolated antioxidant vitamins (particularly vitamins C and E) to protect against exercise-induced oxidative stress, as these supplements can blunt beneficial training adaptations and may increase mortality risk. Instead, athletes should obtain antioxidants through 5+ daily servings of fruits and vegetables. 1

The Critical Distinction: Food vs. Supplements

The evidence clearly separates dietary antioxidants from high-dose supplementation:

• Dietary sources are beneficial: Restricting fruit and vegetable intake to minimal levels (one fruit, two vegetable servings daily) in athletes resulted in decreased serum carotenoids, increased exercise-associated lipid peroxidation, higher ratings of perceived exertion, and increased inflammatory responses. 2

• High-dose supplements are harmful: The American College of Cardiology and American Heart Association explicitly recommend AGAINST prescribing antioxidant vitamin supplements like vitamin E and C, as they interfere with beneficial cellular signaling pathways (Class III recommendation). 1

• UEFA expert consensus: Large doses of individual antioxidant vitamins C and E should be avoided as they interfere with adaptive processes in muscle. 1

Why High-Dose Supplements Backfire

The mechanism explains the paradox:

• ROS are essential signaling molecules: Exercise-generated reactive oxygen species trigger critical adaptations including mitochondrial biogenesis, antioxidant enzyme upregulation, and improved insulin sensitivity. 1

• Supplements block adaptation: High-dose antioxidants competitively interfere with these redox-sensitive signaling pathways, preventing the very adaptations athletes seek. 1, 3

• Antioxidants become pro-oxidants: After exerting their antioxidant effect, compounds like vitamin E produce radicals (tocopheryl radical) that require other antioxidants for regeneration—a synergistic network lost when compounds are isolated. 2

Evidence of Harm from Supplementation

The mortality and morbidity data are concerning:

• Beta-carotene supplementation at 20-30 mg/day increased lung cancer mortality in two major trials (CARET and ATBC). 2

• Vitamin E supplementation at 400 IU/day increased prostate cancer risk (HR: 1.17; 99% CI: 1.004,1.36) and heart failure risk (RR: 1.13; 95% CI: 1.01,1.26). 2

• Systematic reviews conclude: Beta-carotene and vitamin E appear to increase mortality, and higher doses of vitamin A may as well, with no evidence supporting antioxidant supplements for primary or secondary prevention. 2

The Recommended Approach

Prioritize whole food sources:

• Athletes should consume 5+ servings of fruits and vegetables daily to support health, recovery, and performance. 1

• Regular consumption of fresh fruits, vegetables, whole grains, legumes, beans, sprouts, and seeds provides antioxidants in natural ratios that work synergistically. 4, 5

• Increasing phytonutrient intake (fruits, vegetables, nuts, seeds) substantially increases serum carotenoid concentrations and contributes to enhanced recovery and performance. 2

Avoid high-dose supplements during training:

• High-dose isolated vitamin C and E supplements should be avoided during training blocks focused on adaptation. 1

• The dose-response relationship matters—negative effects occur with high-dose supplementation, not physiological amounts from food. 1

Special Circumstances Requiring Caution

Documented deficiencies only:

• If vitamin insufficiencies are documented (e.g., vitamin C deficiency increases oxidative stress and decreases physical performance), correct through diet or targeted supplementation to restore normal levels, then discontinue high-dose supplementation once replete. 2, 1

Limited acute use scenarios:

• Acute ascorbic acid (1000 mg) may modestly reduce endotoxin translocation in exercise-associated gastrointestinal symptoms, but this does not justify routine use. 1

• For exercise-induced bronchoconstriction, dietary ascorbic acid supplementation showed only incomplete inhibition with weak recommendation strength. 1

N-acetyl cysteine exception:

• May provide benefit in the days prior to an endurance event, though this is distinct from chronic vitamin supplementation. 6

Common Pitfalls to Avoid

• Don't assume "more is better": The pharmacologic approach of using supranutritional doses contradicts how nutrition works—food compounds are not drugs. 2

• Don't supplement during heavy training: Chronic intake of combined 1000 mg vitamin C + vitamin E is specifically not recommended during periods of heavy training associated with skeletal muscle adaptations. 1

• Don't confuse oxidative stress markers with outcomes: While most studies show antioxidant supplementation attenuates exercise-induced oxidative stress biomarkers, this has not translated to consistent improvements in muscle damage, performance, or health outcomes. 6, 3

The Bottom Line Algorithm

1. Assess dietary intake: Ensure 5+ servings of fruits and vegetables daily through whole foods. 1, 4

2. Screen for deficiencies: Only if documented deficiency exists, correct to normal levels through diet first, targeted supplementation second. 2, 1

3. Avoid high-dose supplements: Do not use isolated vitamin C and E supplements, especially during training adaptation phases. 1

4. Monitor training response: Adequate fruit and vegetable intake should support recovery without blunting adaptations. 2

This approach maximizes the benefits of exercise-induced oxidative stress as a training stimulus while providing adequate antioxidant support through dietary sources, avoiding the documented harms of high-dose supplementation on both training adaptations and long-term health outcomes. 1, 3