Life expectancy jumped at the end of the last century as medical advances and changes in sanitation made many diseases less common and more curable. Now, we've come to expect that longevity will rise as steadily and inevitably as the cost of living. But, researchers from all over the United States say that this trend may not last forever and that obesity could for the first time ever cause life expectancy to fall.

What the researchers wanted to know: How will trends in obesity affect life expectancy in the United States?

What they did: The researchers used statistics on the life expectancies of people who were obese and those who had an optimum weight to estimate what the life expectancy would be if nobody in the U.S. population were obese. Then they compared that to actual life expectancy of the population as a whole. They extrapolated from that what might happen if obesity rates rose.

What they found: Obesity reduced the life expectancy of Americans by four to nine months. That reduction is greater, the researchers say, than the negative impact on life expectancy of all types of accidental deaths, including accidents and homicides. What's more, the researchers say, because obesity among youth is increasing at a fast clip, its impact on life expectancy is likely to become more pronounced. The researchers speculate that life expectancy will stagnate in five to 10 years, and then begin to decrease as obesity begins picking off the younger generation.

What it means to you: This paper concerns longevity in the population as a whole, so, has little bearing on your daily life. However, the paper does highlight the growing urgency of the obesity epidemic in this country, which, as the researchers point out, could be brought under control if Americans began leading healthier lives.

Caveats: The study does not take into account factors that could have a positive influence on life expectancy, such as advances in medical technology or increased levels of education. In addition, the authors' idea that obesity will reduce life expectancy for future generations is a speculation; it is not proven with any statistical or scientific methods.

Find out more: Look at recent research by The International Longevity Center.

Check out the National Institute on Aging which also conducts studies—they have information on issues that affect the elderly population.

Read the article: Olshansky, S. J. et al. "A Potential Decline in Life Expectancy in the United States in the 21st Century." New England Journal of Medicine. March 17, 2005, Vol. 352, No. 11, pp. 1138-1145.

Abstract online: http://content.nejm.org