WEDNESDAY, March 16, 2005 (HealthDay News) -- America's obesity epidemic could abruptly end the pattern of steady gains in life expectancy seen in modern times, scientists warn in a new report.

Life expectancy at birth is already one-third to three-quarters of a year shorter than it would be if people were to maintain their ideal body weight, the analysis finds. Unless drastic measures are taken to reverse obesity's prevalence, researchers say the life span of the average American could be reduced by two to five years in the coming decades.

"This is not based on speculation about some impending disaster or unforeseen event," said study author S. Jay Olshansky, a professor of epidemiology and biostatistics at the University of Illinois at Chicago. "It is based on the future of American health that we can observe today among the very people who will express the health and life expectancy of the future: today's children."

His team's study, funded in part by the National Institute on Aging (NIA), appears in the March 17 issue of the New England Journal of Medicine.

Because of obesity's toll on human health, researchers also said the number of Americans who will live long enough to cash in on age-entitlement programs in the United States is overstated.

"This is not the way we want to save Social Security and Medicare," added Olshansky, whose collaborators included noted longevity researchers Leonard Hayflick of the University of California, San Francisco, and Dr. Robert N. Butler of the International Longevity Center in New York.

Their sobering outlook stands in sharp contrast to a rosier forecast issued last November by a consortium of 12 federal agencies, including the NIA. In that analysis, researchers predicted a continuation of the historic trend of increasing life expectancy.

Some experts still believe there's reason for optimism.

While an obesity-related reduction in life expectancy is plausible, it is unlikely given offsetting forces that include increased public health education and continuing medical advances, explained Richard M. Suzman, the NIA's associate director for Behavioral and Social Research.

What's more, obesity's effect may already be reflected in life expectancy, he suggested. It may be one reason why gains in U.S. life expectancy at older ages have been less than those of other developed countries in recent years.

"I think there's plenty of head room for life expectancy to continue increasing," Suzman reasoned. He is more concerned about the effects of obesity on disability rates and wishes the authors had spent more time examining this aspect.

Samuel H. Preston, a professor of demography at the Population Studies Center of the University of Pennsylvania in Philadelphia, also questioned the authors' gloomy forecast for longevity. "Hundreds of factors affect a population's rate of death in any particular period, and it is their combined effect that establishes the trend," he wrote in an editorial appearing in the same issue.

Still, he conceded, obesity's rising prevalence and severity could offset positive influences on longevity. "A failure to address the problem could impede the improvements in longevity that are otherwise in store."

The prevalence of obesity among U.S. adults has risen by about 50 percent per decade since 1980, the authors note. Today, two-thirds of adults are overweight or obese. As a result, a growing percentage of the population is at risk for type 2 diabetes, heart disease, cancer and other diseases.

To estimate the overall effect on life expectancy, Olshansky and his colleagues calculated the reduction in death rates that would occur if everyone who is currently obese would shed enough weight to achieve an ideal body mass index.

Based on that analysis, the authors estimated that life expectancy at birth would be 0.33 to 0.93 of a year higher for white men and 0.30 to 0.81 of a year higher for white women. Black men would live 0.30 to 1.08 years longer, and black women would gain 0.21 to 0.73 of a year. Overall, life expectancy would rise one-third to three-fourths of a year if obesity didn't exist, they said.

In other words, that is only the current negative effect of obesity. But if policymakers and public health officials respond to the impending danger that obesity poses, it is not an inevitable consequence, the authors noted.

"In the final analysis, we hope our forecast is wrong because we begin to recognize the significance of the health crisis and act now," Olshansky said. "If we fail, then today's younger generation could live shorter and less healthy lives than that of their parents' generation."

More information

The Federal Interagency Forum on Aging-Related Statistics has more information on life expectancy.

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