Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

If many so-called diseases of aging are preventable, it follows that a slow demise at the end of life is not inevitable. In a celebrated study, the Stanford medical professor James Fries showed that preventive medicine could help people stay healthier for longer through a compression of morbidity. Fries initially based his argument on a massive study that measured life span, disability, and three risk factors for disease (high body weight, smoking, and lack of exercise) among more than twenty-three hundred alumni from the University of Pennsylvania. Predictably, the alums with two or more risk factors died 3.6 to 3.9 years earlier than those with one or no risk factors; perhaps more impressively, they lengthened their period of disability prior to death by 5.8 to 8.3 years.59 Simply put, an unhealthy lifestyle affects morbidity twice as much as mortality.