Antioxidants after training: why extra vitamin C and E don't always help

Antioxidants after training: why extra vitamin C and E don't always help

Muscle soreness, oxidative stress, "free radicals" — it sounds logical to counter that with a generous dose of vitamin C and E. Many endurance athletes take antioxidant supplements around their training, believing it speeds up recovery and protects the body. Research in sports physiology tells a different story: the very oxidative stress that training causes is part of the signal your body uses to adapt. A high dose of antioxidants can dampen that signal.

The study: 11 weeks of training, with and without supplements

Paulsen et al. (2014, The Journal of Physiology, DOI 10.1113/jphysiol.2013.267419) followed 54 healthy young men and women in a double-blind, placebo-controlled RCT. All participants trained 3 to 4 times a week for 11 weeks, mostly endurance running. Half received 1000 mg of vitamin C plus 235 mg of vitamin E daily, the other half a placebo.

The result had two sides:

1. No difference at the performance level. VO2max and the 20m shuttle test improved comparably in both groups — the supplements showed no measurable performance downside at this level.
2. A difference at the cellular level. The usual rise in markers of mitochondrial biogenesis — the production of new energy-generating structures in the muscle cell, a core mechanism of endurance adaptation — occurred only in the placebo group. In the supplement group, that rise was largely absent.

In other words: the training still worked, but part of the biological adaptation that normally comes with it was blunted.

Why would that happen?

Training temporarily increases reactive oxygen species (ROS) in muscle. For a long time these were seen purely as harmful byproducts. It's now clear they also act as signalling molecules: they trigger the cell to build stronger antioxidant defences and more mitochondria — precisely the adaptation that makes endurance exercise so healthy. Flood that cell with a high dose of external antioxidants, and you remove part of that signal before it can do its job. In sports physiology this mechanism is called "mitohormesis": a small, temporary stress that is exactly what's needed to get stronger.

What does this mean in practice?

• Food is not the issue. The study used supplement-level doses (1000 mg vitamin C, 235 mg vitamin E per day) — well above what you get from fruit and vegetables. A varied diet rich in fruit, vegetables and whole grains remains fully recommended; no study has linked those amounts, or that nutrient matrix, to blunted training adaptation.
• Be cautious with high-dose supplements around training. If you train structurally to get fitter (rather than, say, to correct an acute deficiency), there's no strong evidence base for taking megadoses of vitamin C/E around your sessions.
• Context still matters. With a confirmed deficiency, a medical indication, or a period of extremely high training load and infection risk, the balance may look different — that's an individual judgment call, not a blanket rule.
• One study is never the whole story. This is one of the best-known studies in the field, but sports nutrition keeps evolving. The cautious, evidence-based line is: supplement with purpose, not preventively at high dose.

In conclusion

It's a counter-intuitive lesson: not every "healthy" addition around your training amplifies its effect. Sometimes the body does better when you let its own recovery process finish, without stepping in with high doses of isolated supplements.

Wondering whether your nutrition plan is supporting your training goals or quietly working against them? HealthyDNA looks at your full nutrition and training profile, not at isolated supplements.

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