Are a few extra pounds really a danger to your health? Yes, says University of Southern California researcher Jonathan Samet. In fact, being overweight increases the risk of premature death.

While it is widely accepted that obesity is a health risk, the dangers of simply being overweight are debated. Some experts contend that a few extra pounds can even extend life.

But Samet says being overweight definitely doesn't help people live longer. His statement is backed by an analysis of 239 studies that include data from 10.6 million people. The study was published in The Lancet.

"Physicians should identify being overweight as posing a risk to health," said Samet. "Increasing the risk of dying is a powerful indicator of health. The new results on overweight should be strong motivation for people to return to a healthy weight."

According to the World Health Organization, about 39 percent of adults worldwide are overweight, which is defined as having a body mass index (BMI) between 25 and 30. In the U.S. figures are much higher. The National Institutes of Health says that more than two-thirds of American adults are overweight, and more than one-third are defined as being obese.

The new study contradicts an earlier paper in the Journal of the American Medical Association, which found that being overweight actually adds to one's life span, and even obesity with a BMI of 30 to 35 didn't increase mortality.

The new study, however, claims its analysis of previous studies was more strict.

One of the study's limitations, the researchers admit, is the use of BMI as a measurement for visceral fat, which is thought to be the element that causes the risk factors associated with obesity. "BMI is an imperfect measure of fat in someone's belly," Samet said.

However, the researchers say their study found a connection between premature death and being overweight, and say that about 1 in 5 premature deaths in North America could be avoided by having a healthy weight with a BMI between 18.5 and 25.

Health problems associated with being overweight, like those associated with smoking, say the researchers, are substantial but can be prevented.