Free radicals
Unstable, highly reactive molecules with an unpaired electron, produced naturally by metabolism and able to damage cells when in excess (oxidative stress).
Free radicals (reactive oxygen species, ROS) are unavoidable by-products of cellular respiration in the mitochondria. In seeking to recover their missing electron, they « steal » electrons from other molecules (DNA, proteins, membrane lipids), creating chain-reaction damage.
External sources that increase their production: tobacco, pollution, UV, alcohol, fried food, stress, intense exercise.
An original angle (hormesis): free radicals are not purely harmful. In moderate amounts, they are essential signalling molecules
- They trigger immune defences (white blood cells use them to kill pathogens)
- They signal adaptations to exercise (muscle strengthening, mitochondrial biogenesis)
- They take part in autophagy (cellular clean-up)
This principle is called hormesis: a low dose of stress (here oxidative) strengthens the body, while a high dose destroys it. This is why exercise (which temporarily generates free radicals) is beneficial.
A counter-intuitive corollary: taking antioxidants straight after exercise can cancel its benefits, by neutralising the hormetic signal needed for adaptation.
The optimal balance is therefore not « zero free radicals » but a dynamic balance between production and defence systems (enzymes such as superoxide dismutase, glutathione, plus dietary antioxidants).