Oxidative stress

Oxidative stress is an imbalance between reactive oxygen species, often loosely called free radicals, and the body's capacity to neutralise them. Those molecules are produced continuously as a by-product of aerobic metabolism, so this is a normal state to manage rather than a contamination to eliminate.

They are not purely destructive, which is the part the supplement aisle omits. Reactive oxygen species act as signalling molecules, and they are part of how the immune system kills pathogens and how muscle senses that it has been trained.

That signalling role is why blanket antioxidant supplementation has disappointed so consistently. High dose vitamin C and E around training can blunt some of the adaptations that training is meant to produce, and large trials of antioxidant supplements have generally failed to show the benefits the mechanistic story predicted.

Chronic excess is still worth avoiding, and it is associated with ageing, cardiovascular disease and neurodegeneration. The sensible target is the inputs that generate it: smoking, excess alcohol, poor sleep, obesity and chronic overreaching in training.

Exercise is the interesting case. A session generates a burst of oxidative stress, and regular training raises the body's own antioxidant defences, so the net effect of consistent exercise is a more capable system. This is hormesis: a small stress that provokes an adaptation larger than the insult.

Food beats pills here, as it usually does. Fruit, vegetables, herbs and whole grains supply a wide range of compounds alongside fibre and micronutrients, and the outcome evidence for eating them is far stronger than for any isolated antioxidant.

In practice, do not take high dose antioxidants around training expecting a benefit, and treat oxidative stress as a reason to fix sleep and smoking rather than a reason to buy a supplement.