Antioxidant Supplementation and Endurance Performance
High-dose antioxidant supplementation (particularly vitamins C and E) should not be used by endurance athletes, as it may impair training adaptations without improving performance, and whole food sources of antioxidants through fruits and vegetables should be prioritized instead. 1
Key Guideline Recommendations
The most authoritative guidance comes from major sports medicine organizations:
The American College of Cardiology and American Heart Association explicitly recommend against antioxidant vitamin supplements (Class III recommendation), as they interfere with beneficial cellular signaling pathways 1
The UEFA expert statement on elite football nutrition specifically advises against large doses of individual antioxidant vitamins C and E, as they interfere with adaptive processes in muscle 1
The Critical Distinction: Food vs. Supplements
Athletes should consume 5+ servings of fruits and vegetables daily to support health, recovery, and performance through whole food antioxidant sources 2, 1:
Short-term restriction of fruit and vegetable intake in athletes resulted in increased exercise-associated lipid peroxidation, higher ratings of perceived exertion (RPE), and increased inflammatory responses 2
Increasing phytonutrient intake from whole foods (fruits, vegetables, nuts, seeds) substantially increased serum carotenoid concentrations and contributed to enhanced recovery and performance in world-class endurance athletes 2
This dietary approach is fundamentally different from high-dose antioxidant supplementation, which carries well-established risks of blunting adaptation 2
Why Supplements Impair Performance
Exercise-generated reactive oxygen species (ROS) serve as essential signaling molecules for training adaptations, including mitochondrial biogenesis, antioxidant enzyme upregulation, and insulin sensitivity improvements 1:
High-dose antioxidants block these beneficial signaling pathways, leading to impaired exercise adaptations 1, 3
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, 4
Antioxidant supplementation can attenuate endurance training-induced enhancements in antioxidant capacity, mitochondrial biogenesis, cellular defense mechanisms, and insulin sensitivity 3
Evidence Quality and Consistency
The research evidence consistently shows no performance benefit:
A 2020 comprehensive review concluded there is a lack of supportive evidence for most antioxidant compounds to recommend to athletes 4
A 2015 meta-analysis found that chronic intakes of most antioxidants have a harmful effect on performance 5
A 2011 review stated there is limited scientific evidence to recommend antioxidant supplements to athletes or physically active individuals 6
Importantly, there is no convincing evidence that antioxidant supplementation enhances exercise-training adaptations 3
Special Circumstances
For individuals with documented vitamin deficiencies, correcting insufficiencies through diet or targeted supplementation to restore normal levels is appropriate, but high-dose supplementation should be discontinued once replete 1:
Vitamin insufficiencies (e.g., vitamin C) increase oxidative stress and decrease physical performance 2
The negative effects are primarily seen with high-dose supplementation, not physiological amounts from food 1
Common Pitfalls to Avoid
Do not use high-dose isolated vitamin C and E supplements during training blocks focused on adaptation 1
Avoid the misconception that reducing exercise-induced inflammation is beneficial—some inflammation is necessary for adaptation 1
Do not confuse the benefits of whole food antioxidants with the risks of high-dose supplementation 2, 1
Recognize that acute administration immediately before exercise may have different effects than chronic supplementation, but this does not justify routine use 1, 7