A Potential Decline in Life Expectancy in the United States in the 21st Century

Abstract

Estimates of future life expectancy strongly influence public policy on age-based entitlement programs such as Social Security and Medicare. Although recent estimates of how long Americans will live in this century have predicted an increase, the authors believe that current trends in obesity in the United States may end the slow but steady increase in life expectancy that has taken place in the past 2 centuries. In the past 3 decades, the rise in life expectancy at birth has decelerated in the context of historical trends. Recent exploration by experts, including mathematical demographers, predicts a more rapid rate of increase in life expectancy for the U.S. population than has been anticipated. At present, however, there is no life-extending technology that might lead to much higher estimates of life expectancy and, even if such technology is developed, it would have to be widely implemented before influencing statistics on population levels. Potential technology does not warrant revising forecasts of life expectancy. Since the 1970s, obesity has become approximately 50% more prevalent per decade. Fully two thirds of U.S. adults now are obese or overweight. Extreme obesity has increased at a particularly rapid rate. Obesity is associated with an increased risk of type 2 diabetes, coronary heart disease, cancer, and other conditions. Being overweight in childhood increases the risk of death from any cause and also death from cardiovascular disease in men and cardiovascular morbidity increases in both men and women. Unless measures are taken to halt the rising prevalence of obesity, an increased risk of many fatal and nonfatal conditions can be expected as people become older. The authors have estimated the effect of obesity on life expectancy in the United States by determining the reduction in death rates that would occur should every person who currently is obese were to lose enough weight to achieve an “optimal” body mass index of 24 kg/m2. A conservative estimate is that life expectancy at birth in the United States would, if there was no obesity, be higher by 0.33 to 0.93 year for white males, 0.30 to 0.8 year for white females, 0.30 to 1.08 year for black males, and 0.21 to 0.73 year for black females. If current rates of death associated with obesity remain the same in this century, life expectancy would decline from one third to three fourths of a year. This is greater than the negative effect of all accidental deaths combined, and in time it probably would rapidly approach—or exceed—the negative effects on life expectancy of ischemic heart disease or cancer. Young people today may live less healthy and possibly shorter lives than their parents. The authors believe that the life-shortening effect of obesity could increase to 2 to 5 years or even more in the coming decades as younger obese individuals carry their increased mortality risk into middle age and old age.