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In an article recently published in the New England Journal of Medicine (Olshansky et al., 2005), we predicted that the steady rise in life expectancy in the United States in this century may soon come to an end because younger people today are far less healthy than previous cohorts of younger people.
We estimated that if obesity did not exist in the U.S. today, life expectancy at birth would be higher by approximately 4–9 months. We further estimated that if the observed relationship between obesity and mortality remains constant, then the rise of childhood obesity in the past two decades will, by the middle of this century, lead to a reduction of 2–5 years in life expectancy.
Our calculations were based not on estimates of the number of deaths attributable to obesity (which remains the subject of great debate), but rather on the observed relationship between body mass index (BMI) and the risk of death among people in the U.S. between the ages of 20 and 85, based on health survey data. One of the most important points we make is that the negative health and life expectancy consequences of the rise of childhood obesity have yet to be realized.
When such problems do arise, we anticipate that it will occur in three phases. The first phase, which we can already measure because it is here today, is the rising prevalence of obesity among young children. The second phase, which we are just beginning to observe, is the manifestation of obesity-induced health conditions that were rarely or never before seen in young people. The rise of type II diabetes in children is an example of a condition that was unheard of in children just 30 years ago—it is now occurring among obese children with an alarming frequency. The third phase will be obesity-induced mortality over the next 50 years as these children begin living into their third through sixth decades of life, which is when obesity begins to kill. It is during this third phase in the coming decades when life expectancy in the U.S. could begin to decline.
The rise of childhood obesity in the U.S. is roughly equivalent in scope to the introduction of a behavioral habit that has a harmful but delayed effect on morbidity and mortality. For example, if we were a nation of mostly nonsmokers and within two decades discovered that the prevalence of smoking among children increased from negligible levels to 20–30%, the short-term health effects would be minimal, but the long-term effects would be devastating. This is the prospect we face with today’s childhood obesity epidemic: the most detrimental health and longevity effects will not be seen for decades. This is a phenomenon that cannot be detected by current methods used to forecast life expectancy or estimate the number of deaths currently attributable to obesity. The reduction in life expectancy due to obesity is not trivial—it is larger than the negative impact of all accidental deaths combined, and there is reason to believe that it will rapidly approach and could exceed the negative impact that ischemic heart disease or cancer has on life expectancy.
Can the problem be fixed? Genetic factors clearly affect body weight and risk of obesity. Since in the past three decades our genes have not changed but obesity prevalence in the U.S. tripled, the obesity epidemic can be attributed to adverse influences in the environment affecting food intake and activity level.
Advanced training in nutrition is not required to understand the nature of these influences: pervasion of our diet by high-calorie, low-quality foods and beverages, driven by massive marketing campaigns; placement of junk food in school vending machines; deterioration of the school lunch program; cut-backs or elimination of physical education classes and after-school sports programs; land-use policies that favor development over preservation of open spaces for recreation; increasing sedentary activities, especially television viewing; stress on families, leaving little time for busy parents to supervise their children’s diet and physical activities; and limited funding for obesity prevention and treatment.
Ultimately, the solution to the obesity epidemic is simple, but it will require fundamental change on many levels of society. Of course, consumers and parents bear some responsibility for their choices and the behavior of their children. However, the food industry can become part of the solution, not part of the problem, with action that is ultimately in its own long-term self-interest. After all, since Americans aren’t going back to the farm any time soon, we need the food industry to feed us. There are profits aplenty for companies willing to market, in a socially responsible manner, products that are both healthful and appealing.
by S. Jay Olshansky,
School of Public Health,
University of Illinois at Chicago, 1603 W. Taylor St., Chicago, IL 60612
by David S. Ludwig,
Obesity Program, Children’s Hospital Boston, 300 Longwood Ave, Boston, MA 02115
Olshansky, S.J., Passaro, D., Hershow, R., Layden, J., Carnes, B.A., Brody, J., Hayfl ick, L., Butler, R.N., Allison, D.B., and Ludwig, D.S. 2005. A potential decline in life expectancy in the United States in the 21st century. New Eng. J. Med. 352: 1103-1110.