What is considered a high dose of vitamin C (Vitamin C) that interferes with resistance training adaptations?

High-Dose Vitamin C and Resistance Training

High doses of vitamin C (1000 mg/day) combined with vitamin E (235 mg/day) are not recommended during resistance training, as this combination may blunt training adaptations and reduce skeletal benefits in athletes. 1

Defining "High Dose" in the Training Context

The specific threshold identified in sports medicine research is 1000 mg/day of vitamin C, particularly when combined with vitamin E supplementation. 2, 3

• This dosage has been consistently studied across multiple randomized controlled trials examining resistance training adaptations 2, 4, 5
• The UEFA expert group statement explicitly warns against "large doses of individual antioxidant vitamins C and E" interfering with adaptive processes in muscle 1
• This is substantially higher than the recommended daily intake of 50-100 mg/day for healthy individuals 1

Mechanisms of Interference with Training Adaptations

Reducing exercise-induced muscle inflammation and free radical production with large doses of antioxidants may interfere with adaptive processes in muscle and is therefore discouraged. 1

• High-dose vitamin C (1000 mg/day) prevents exercise-induced expression of key transcription factors involved in mitochondrial biogenesis, including peroxisome proliferator-activated receptor co-activator 1, nuclear respiratory factor 1, and mitochondrial transcription factor A 6
• Antioxidant supplementation may shut down redox-sensitive signaling pathways in exercised muscle fibers that are essential for training adaptations 2
• The combination of vitamin C (1000 mg) and vitamin E (235 mg) reduced strength training-induced improvements in areal bone mineral density by approximately 1% at the total hip and 0.9% at the lumbar spine in elderly men 5

Evidence Quality and Consistency

The evidence against high-dose supplementation during resistance training is robust:

• A 2023 systematic review of 14 randomized controlled trials found that 11 studies showed either neutral or negative effects of high-dose vitamin C supplementation on muscle damage, physical performance, perceived muscle soreness, and/or adaptations to training 3
• Only 3 studies showed positive outcomes related to decreased markers of muscle damage, but these benefits did not translate to improved performance 3
• A double-blind randomized study specifically testing 1000 mg/day vitamin C plus 235 mg/day vitamin E found no beneficial effects on heat shock proteins or endogenous antioxidant adaptations during 12 weeks of strength training 4

Practical Recommendations for Athletes

Athletes should obtain antioxidants through a nutrient-rich diet instead of through supplement use, avoiding long-term high-dosage supplementation with vitamin C. 3

• The recommended intake for chronic disease prevention is 200-500 mg/day, which is well below the threshold that interferes with training 1
• Food sources and dietary supplements have comparable bioavailability, but dietary intake through fruits and vegetables provides additional beneficial nutrients 7
• Occasional intake of vitamin C at physiologic doses (200-500 mg/day) for general health is acceptable and does not interfere with training adaptations 1

Critical Caveats

• The interference with training adaptations appears most pronounced when vitamin C is combined with vitamin E supplementation 2, 4, 5
• Age may potentially modulate the response, though studies in elderly men still showed negative skeletal effects from high-dose supplementation during resistance training 5
• Short-term use (less than 4 weeks) has not been as extensively studied, but the negative effects on mitochondrial biogenesis can occur within weeks of supplementation 6

Clinical Algorithm for Vitamin C Use in Athletes

1. Avoid supplementation above 1000 mg/day during active resistance training periods 1, 2, 3
2. Prioritize dietary sources of vitamin C to meet basic requirements (50-100 mg/day) 1
3. If supplementation is desired for general health, limit to 200-500 mg/day 1, 7
4. Never combine high-dose vitamin C with vitamin E during training cycles 1, 5
5. Reserve higher doses (2-3 g/day IV) exclusively for acute critical illness, not athletic performance 1