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Modestly overweight baby boomers will live shorter lives, two studies will report tomorrow in The New England Journal of Medicine.

That fits with the conventional wisdom of many public health experts who cite the increased risk of heart disease and cancer. But it runs counter to a study last year by researchers at the Centers for Disease Control and Prevention and the National Cancer Institute that found slightly overweight people had a somewhat lower risk of death.

One of the two new studies looked at more than 500,000 members of AARP, an organization for people 50 and older. Over 10 years, more than 61,000 of them died. 

Among women, the risk of death increased for any amount of weight above the normal range. For men, the risk was not higher for those merely overweight.

The researchers said the more telling analysis arose when they focused on 186,000 healthy men and women who had never smoked. Among men and women, being overweight raised the risk of death 20 percent to 40 percent compared with normal-weight people, the researchers said.

Obese people had a risk two to three times that of normal-weight people.

“We found that people who are overweight had a modestly increased risk of premature death,” said Dr. Michael F. Leitzmann, an investigator at the National Cancer Institute and the senior author of the article.

Because all the participants were recruited from AARP, they are not exactly representative of the population as a whole, and the participants reported their weight themselves, which contributes to some uncertainty in the results. 

Dr. Leitzmann said neither factor would probably skew the results considerably because “it’s a very large sample of people.” 

Errors in reporting weights — people sometimes say they weigh less than they actually do — would also not produce a large effect, he added. 

Researchers have almost universally found that obese people have considerable health risks. But there has been debate over whether someone who is less severely overweight is at a greater risk of illness. Other factors, especially smoking, can complicate analysis of the data. Smoking greatly increases the chances of deadly lung diseases, but smokers tend to weigh less.

“No single study is able to solve a controversy of this magnitude,” Dr. Leitzmann said, but he recommended that anyone overweight “should be looking to lose weight.”

As with most such studies, the fatness and thinness of the participants was specified by their body mass index, defined as their weight in kilograms divided by the square of their height, measured in meters.

A second study by researchers at Yonsei University in Seoul, South Korea, and Johns Hopkins University looked at 1.2 million Koreans ages 30 to 95 and followed them for 12 years. The researchers looked at 82,372 deaths and correlated them with the body mass index. They found, too, that risk of death and cancer increased in people who were overweight, but not obese.

“It’s the first time an Asian population this large has been studied,” said Dr. Eliseo Guallar, a professor of epidemiology at the Johns Hopkins School of Public Health and an author of the paper.

The diet and lifestyle of Asians differ considerably from those of Americans, as does physiology. An Asian with the same body mass index as a white typically has a higher percentage of fat, so doctors recommend that Asians maintain a lower weight. 

The Koreans in the study were much thinner than typical Americans, with an average body mass index of 23.2 compared with 28 for Americans. The overweight category runs from 25.0 to 29.9.

Dr. Guallar said the findings suggested to him that keeping weight in what is regarded as a normal range was a good idea. “That will help control a whole bunch of other big problems,” he said.

As an example, according to the body mass index, someone who is 5 foot 9 would be considered overweight at 169 pounds; he would be considered obese at 203 pounds. 

Dr. Meir Stampfer, chairman of the epidemiology department at the Harvard School of Public Health who was not involved in either study, called both articles fine. 

“They show quite convincingly, yet again, that overweight and, in particular, obesity, raise the risk of mortality,’’ Dr. Stampfer said. “It really should be the final word on this issue that’s arisen as to whether overweight is actually bad for you or not.”