Antioxidant supplements
Evidence: moderate
High-dose vitamin C and E may blunt the training adaptations you are trying to build. Get antioxidants from food, not from chronic megadoses.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Keep it in proportion
The basics are where the real gains are: consistent volume, sleep and adequate fuelling. Weigh anything below honestly, and do not let a marginal or over-marketed aid pull attention from the things that actually move the needle.
High-dose antioxidant supplements are a case where the evidence points to potential harm to adaptation, not benefit. This makes them more than merely useless: routine megadosing around training may work against the runner taking them.
The key study gave 1000 mg of vitamin C and 235 mg of vitamin E daily for 11 weeks and found it blunted the molecular signals of mitochondrial adaptation, with markers rising in the placebo group but not the supplemented one (Paulsen et al. 2014). The mechanism is that exercise-induced reactive oxygen species are not just damage, they are required signals that tell the muscle to adapt, and swamping them with antioxidants suppresses the message.
The honest nuance: in that study VO₂max and performance improved equally in both groups over 11 weeks, so the blunting was molecular and not a demonstrated whole-body performance loss. But the authors still advised caution, and the direction is consistent with the redox-signalling literature. The reasonable position is to get antioxidants from a diet rich in fruit, vegetables and polyphenols, and to avoid chronic high-dose supplementation during adaptation-focused training. The same caution applies to taking tart cherry and similar polyphenol products daily rather than reserving them for acute recovery.
What to do instead
Food, not pills
Eat a varied diet rich in fruit, vegetables and other whole plant foods. These deliver antioxidants in the modest amounts and mixed forms the body evolved with, alongside fibre and other nutrients, and at those doses there is no evidence they blunt adaptation. The problem is specifically the isolated high-dose supplement, not the antioxidants in food.
When a short course might be reasonable
The blunting concern applies to chronic high-dose use during adaptation-focused training. There are narrow situations where a brief course could be justified despite this, for example prioritising rapid recovery during a dense competition block when adaptation is not the goal, the same logic as cold water immersion. Even then the evidence of benefit is weak, so the default for a healthy runner is to skip the supplement and get antioxidants from the plate. This also covers the popular polyphenol products such as tart cherry: useful at most for acute recovery, not as a daily training-block habit.