Americans are facing the first sustained drop in life expectancy in modern history because of the rapid rise in obesity, according to a provocative new analysis.
Average life spans in the United States, which have been steadily increasing over the past century, could be shortened by two to five years in coming decades unless aggressive efforts are taken to slow the obesity epidemic, a diverse group of 10 scientists contends in an article published today in the New England Journal of Medicine.
“The youth of today may, on average, live less healthy and possibly even shorter lives than their parents,” writes the group of scientists, led by University of Illinois demographer S. Jay Olshansky.
Already, they calculate, illnesses caused by obesity have reduced life expectancy in the United States by four to nine months. That is more than the combined effect of car crashes, homicides and suicides, and it approaches the effects of heart disease and cancer on life expectancy.
Currently, the life expectancy for someone born in the United States is 77.6 years. Except for disease outbreaks and wars, that statistic has been steadily rising since the mid-1800s.
The new report — part scientific analysis, part call to action — says that the easy gains in longevity, such as curing childhood illness, have been made. Current methods for calculating life expectancy, it argues, need to be reassessed in light of the oncoming obesity epidemic.
“Forecasting life expectancy by extrapolating from the past is like forecasting the weather on the basis of its history,” the scientists write. “Looking out the window, we see a threatening storm — obesity — that will, if unchecked, have a negative effect on life expectancy.”
Estimates of U.S. life spans, they noted, have important implications for government policy. Federal tax rates as well as benefits from social-entitlement programs, such as Social Security and Medicare, are all based in part on life expectancy projections for the nation’s population.
The authors of the new analysis are respected scientists in a variety of fields, including Leonard Hayflick, a cell biologist and longevity specialist at UCSF, and Dr. Robert Butler, a former director of the National Institute on Aging.
But their analysis drew criticism from some longevity experts, who said that while obesity was a major public health concern, the report’s projections were overly pessimistic.
“The claim that obesity will bring a halt to gains in life expectancy is entirely speculative and not based on any sound methodology,” said Samuel Preston, a University of Pennsylvania demographer who wrote an editorial that disagrees in part with the article in the same issue of the journal.
Preston said the authors didn’t give enough weight to factors such as medical research and rising education levels that can increase life expectancy.
Still, few disputed the significance of obesity as a public health problem. Today, two-thirds of U.S. adults are overweight, including one-third who are obese, as measured by the body mass index, a standard measurement of height and weight. Current trends indicate that the prevalence of obesity will continue to rise and affect ever younger age groups.
Minority groups have seen especially sharp increases in childhood and adult obesity.
Obesity significantly increases the risk of death from a variety of health problems, including diabetes, cancer and heart disease. Among the severely obese, life expectancy is reduced by an estimated five to 20 years, according to one study.
Using data from a large federal assessment of obesity rates, the researchers calculated how much longer life expectancy would be if everyone who is currently obese were to lose enough weight to obtain an optimal body mass index of 24.
If obesity did not exist, the authors “conservatively estimated” that life expectancy would be four to 11 months longer for white men, four to 10 months longer for white women, four to 13 months longer for black men and three to nine months longer for black women.
The authors said the estimate was conservative in part because it focused only on adults. As obese children age, “the life-shortening effect of obesity could rise from its current level of about one-third to three-fourths of a year to two to five years, or more, in the coming decades,” they wrote.
Richard Suzman, associate director of the National Institute on Aging, which provided funding for the study, said the analysis broke new ground. “This work paints a disturbing portrait of the potential effect that lifestyles of Baby Boomers and the next generation could have on life expectancy,” he said.
The sharp increase in obesity among Americans in their 60s may help explain why the gains in U.S. life expectancy at older ages have been less than those of other developed nations, Suzman said. More than 20 countries, including France, Japan, Germany, Sweden and Britain, have a higher life expectancy. Women in Japan, for example, live about five years longer than women in the United States.
But Suzman and others said the reduction in life expectancy was not inevitable.
“There is room for optimism,” he said. “The National Institutes of Health and other parts of the Public Health Service have recognized that this is a serious health problem and begun to take action. It’s theoretically reversible.”
