Couch potato: The antithesis of hormesis

The impact of hormesis on health can be further appreciated by consideration of the couch potato lifestyle. When cells in the body and brain are not challenged, they become complacent and are therefore vulnerable to injury and disease. Lack of physical and mental exercise, in combination with excessive food intake, results in a condition called insulin resistance that is a harbinger of diabetes and cardiovascular disease. On the other hand, when fewer calories are consumed and when more energy is expended (exercise), cells are subjected to a mild metabolic stress. They respond to this mild stress adaptively by increasing their ability to take up glucose in respond to insulin. This hormesis response is, in part, responsible for the ability of dietary energy restriction and exercise to ward off diabetes and cardiovascular disease. However, obesity and diabetes are not the only adverse physiological consequences of being a couch potato. Exercise and dietary energy restriction improve the functional efficiency of the heart and gut through a hormetic mechanism that involves increased activity of the parasympathetic component of the autonomic nervous system. As a consequence, heart rate and blood pressure are decreased and gut motility is increased, thereby reducing the risk of heart disease, stroke, and colon cancer. Relatively underappreciated is the contribution of the lack of mental challenges to the poor health associated with the couch potato lifestyle. Individuals who engage in intellectually challenging occupations or hobbies may be at reduced risk for Alzheimer's disease because of the beneficial stress imposed on the neurons when they are challenged. Studies have shown that neurons respond to mental and physical activity by increasing their production of neurotrophic factors that may help them to resist disorders such as Alzheimer's disease and Parkinson's disease.