The Associated Press

A study of more than 1 million Americans provides the most convincing evidence yet that simply being overweight can cut your life short.

The study, the largest ever done on obesity and mortality, found that overweight people run a higher rate of premature death. And this was true even among people who didn't smoke and were otherwise healthy during their middle years.

The study was conducted by the American Cancer Society and published in Thursday's New England Journal of Medicine.

It settles once and for all any lingering questions about whether weight alone increases the risk of death and disease, said Dr. JoAnn Manson, a Harvard University endocrinologist and preventive-health specialist.

"The evidence is now compelling and irrefutable," Manson said. "Obesity is probably the second-leading preventable cause of death in the United States after cigarette smoking, so it is a very serious problem."

The study found an especially clear association between excess weight and a higher risk of dying from heart disease or cancer.

And unlike a similar study last year that suggested being overweight is less of a problem as people grow older, this study found many more deaths among overweight people of all ages, especially those over 75.

More adults and children are overweight than ever before, with 55 percent of American adults weighing more than they should.

"The message is we're too fat and it's killing us. We need to come up with ways as a society to eat less and exercise more," said American Cancer Society epidemiologist Eugenia Calle, lead author of the study.

Manson said: "It's going to take a coordinated campaign to turn this around, at the community level, at the environmental level, with changes in the food industry and marketing industry, having more bike paths and sidewalks."

Black women were found to be the only exceptions to the rule. The study found the most obese black women did not have a significantly higher risk of premature death than slender black women.

That poses a fascinating scientific riddle, said June Stevens, a University of North Carolina professor of nutrition. "Although I had seen this in several other studies, I wasn't ready to believe it was true," she said. "Now I'm thinking maybe this is true, and we need to figure out why."

Still, Stevens and Manson said the study probably understates the risks of obesity for black women.

They pointed out that slender, non-smoking black women have a higher risk of death to begin with than their white counterparts, probably because they have less access to health care than white women and more undetected disease. That makes it appear that weight alone doesn't play a big role in death rates among black women.

"It would be really unfortunate if we became more complacent about obesity in blacks than in whites," Manson said.

The researchers studied participants in the national Cancer Prevention Study II from 1982 through 1996. The average age at enrollment was 57.

The researchers calculated each subject's body mass index, or BMI, a ratio of weight to height, and tracked them for age and cause of death. The results were adjusted for age, education, physical activity, alcohol use, marital status, use of aspirin as a blood-thinner, consumption of fats and vegetables, and use of estrogen supplements.

Among healthy, non-smoking white men and women and black men, the researchers found a gradually increasing risk of death beginning with a BMI of 25, which is 150 pounds for a 5-foot-5 woman and 174 pounds for a 5-foot-10 man.

The fattest white men, with a BMI of 40 or more — 278 pounds on a 5-foot-10 frame — were 2.58 times more likely to die than their healthiest peers, men of the same height weighing 153 to 170 pounds. White women with a BMI of 40 or greater — 240 pounds for a 5-foot-5 woman — were twice as likely to die as their counterparts who weighed 132 to 148 pounds.

Thin men and women also had higher death rates, but it was not clear whether their low weight was a cause or an effect of disease.

Copyright 1999 The Associated Press. All rights reserved.