Hormesis
Why small doses of stress make the body stronger
Definition
Hormesis is the biological phenomenon in which low-intensity exposures to a stressor produce beneficial effects, while high doses of the same agent are harmful. The hormetic curve is an inverted U-shape. The fundamental principle: moderate stress activates cellular defence mechanisms that more than compensate for the initial damage, leaving the organism more resilient than before.
Detailed explanation
The most relevant examples in longevity are:
Extreme temperature: sauna at 80–100 °C activates heat shock proteins (HSPs), which are molecular 'chaperones' that repair damaged proteins. Cryotherapy at -130 °C activates the cold response (norepinephrine, adiponectin). Heat-cold contrast amplifies both responses.
Exercise: muscle damage induced by intense exercise activates repair and supercompensation, resulting in greater muscle mass and strength.
Intermittent fasting: caloric restriction activates autophagy, sirtuins, and AMPK — all key regulators of ageing.
Low-dose UV radiation: stimulates vitamin D and melanin production, defence mechanisms against oxidative damage.
The concept was formalised by toxicologist Edward Calabrese and is now central to the biology of ageing: it is not 'living protected' but rather 'living exposed to controlled doses of stress' that optimises longevity.
Related terms
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