Hormesis is the phenomenon in which low doses of stressors that are normally toxic instead strengthen the organism, and make it more resistant to higher doses of toxins or stressors. Low doses of ‘toxin’ may make you healthier.
Exercise and calorie restriction are examples of hormesis. Exercise, for example puts stress on muscles causing the body to react by increasing strength. Weight bearing exercise puts stress on bones, which causes the body to react by increasing the strength of those bones. Being bed ridden or going into zero gravity, as with astronauts causes rapid weakening of the bones.
Calorie restriction can be considered a stressor and causes a rise in cortisol, commonly known as the stress hormone. This lowers inflammation and increases the production of heat shock proteins. Low levels of stress increases resistance to subsequent stressors. So, calorie restriction satisfies the requirements of hormesis. Because both exercise and calorie restriction are forms of stress, they involve the production of free radicals.
Hormesis is not a rare phenomenon. Alcohol, for example, acts via hormesis. Moderate alcohol use is consistently associated with better health than complete abstention.
Some of the beneficial effects of certain foods may be due to hormesis. Polyphenols are compounds in fruits and vegetables, as well as coffee, chocolate, and red wine, and they improve health, possibly in part by acting as low-dose toxins.
Why is hormesis important for aging?
Other theories of aging presuppose that all damage is bad, and accumulates over time. But the phenomenon of hormesis shows the body has potent damage-repair capabilities that can be beneficial when activated. Take exercise as an example. Weight lifting causes microscopic tears in our muscles. That sounds pretty bad. But in the process of repair, our muscles become stronger. Gravity puts stress on our bones. Weight bearing exercise, such as running causes micro-fractures of our bones. In the process of repair, our bones become stronger. The opposite situation exists in the zero gravity of outer space.
Without the stress of gravity, our bones become osteoporotic and weak. Not all damage is bad — small doses of damage are in fact good. What we are describing is a cycle of renewal. Hormesis allows breakdown of tissue like muscles or bones that are then rebuilt to better withstand the stress placed upon them. Muscles and bones grow stronger. But without breakdown and repair, you cannot get stronger.
