What is hormesis (what doesn't kill you makes you stronger)?
Hormesis is a well-described biological principle: a low dose of stress can make your cells more resilient, provided the dose and recovery are right. Exercise is the best-supported example; for other stressors in people, the evidence is still limited.
Hormesis is the phenomenon in which a low dose of something that is harmful in larger amounts actually produces a beneficial effect. The response curve takes an inverted-U shape: a little stress helps, too much is damaging. Many studies combined, covering thousands of papers, found this pattern in around 350 cases examined, across a wide range of organisms and substances. The maximum stimulating effect at a low dose was, on average, about 50% higher than at zero exposure.
The mechanism: cells respond to mild stress by switching on systems that produce protective proteins, including enzymes that neutralise harmful substances and proteins that repair other damaged proteins. This 'tune-up' leaves the cell better equipped to handle the next challenge. Timing is key: periodic stress gives that tune-up room to work, while continuous stress overwhelms the system.
The best-known example is physical exercise. Training causes temporary muscle damage and stress in your body's cells, but your body adapts and grows stronger. This improves heart function, muscle mass and your immune defences. Overtraining reverses the benefit: exercising too much and too often leads to greater damage and a higher risk of infections. The hormesis zone sits somewhere between complete inactivity and overtraining.
In animal studies, exposure to mild stressors such as temperature fluctuations, low doses of reactive substances or calorie restriction sometimes extends lifespan. This is linked to greater resilience in the organism. The effects are modest, however, and depend on the right dose at the right time. Calorie restriction and intermittent fasting work through similar routes, but whether this leads to the same extension of lifespan in people has not been proven.
Plant compounds such as sulforaphane (found in broccoli), curcumin and resveratrol activate similar protective processes in cells at low doses. At high doses, those same substances can be harmful. Whether you actually benefit from them in practice, through food or supplements, has not been sufficiently demonstrated in people, so do not overclaim.
All sources are reviews; there are no trials where people were randomly assigned to groups, or combined analyses of multiple studies, in the reference list. The mechanistic findings come largely from experiments with cells and animal studies. The evidence for exercise as a hormetic stressor is the most solidly supported. That hormesis influences ageing and lifespan in people has not been demonstrated.
Does rapamycin help people live longer in good health?
Rapamycin works in mice, but whether it also leads to a longer and healthier life in humans has not yet been demonstrated. Side effects are real, long-term data in healthy people are absent, and use outside a clinical context cannot currently be justified.
Can heat, such as a sauna, damage your cells or actually make them stronger?
Moderate heat briefly damages cells, but simultaneously triggers a repair response that makes the cell more resilient. Repeated sauna use appears beneficial for inflammation levels, immune function, and possibly blood sugar as well, but large randomised studies are still lacking.
Does metformin help you stay healthy for longer?
Metformin can largely prevent diabetes in people with prediabetes or metabolic syndrome, and that brings real health benefits. Whether it also slows ageing in healthy people has not yet been demonstrated.
Does turmeric help against inflammation?
Curcumin demonstrably lowers inflammation markers in the blood, with the strongest evidence for CRP. For joint complaints the results are positive but preliminary; doses of a few hundred milligrams per day appear to be safe.
Is curcumin well absorbed by your body?
Ordinary curcumin without any addition is barely absorbed by the body; choose a product with piperine (black pepper extract) or a specialised formulation to notice any effect.
Which health interventions have the greatest impact on living longer?
Exercise, a Mediterranean diet, adequate sleep, social contact and quitting smoking each have a measurable influence on how long you live in good health. Combining several healthy habits brings the greatest benefit.