Researchers from the Harvard School of Public Health, led by Dr. Frank Hu, made the finding by analyzing data from over 102,000 female nurses who took part in a study that began in 1989.

At the onset, the women, who were between the ages of 24 and 44, filled out a questionnaire. They provided their current weight and height, as well as weight at the age of 18. That information allowed the researchers to calculate their body mass index, or BMI, which is a standard height, weight measurement used to assess an individual's status as normal, overweight or obese.

They were followed for a period of up to 12 years -- to the end of their study or to their death, if they did not survive the entire study period. During that time, 710 of the participants died.

Even Moderate Overweight Is Risky

Details about other health issues, such as consumption of alcohol, smoking, amount of exercise and medical history, were gleaned from the participants' questionnaires.

The researchers found that women with a higher BMI at the age of 18 were likely to drink and smoke more and exercise less during adolescence than their normal-weight counterparts. And those with BMIs indicating obesity at the age of 18 had three times the risk of dying during middle age.

Even those who were only moderately overweight as adolescents had a higher risk of dying prematurely, the study found.

Compared to those with a lower BMI, those who had been overweight during adolescence but never had smoked also were likely to die at a younger age.

Teenage Obesity Epidemic Spreading

Health experts fear the consequences of childhood obesity may include a lower life expectancy overall. Teenage obesity is growing at an alarming rate in many parts of the world, particularly in developing nations. More than 15 percent of US teens are overweight.

The study highlights the importance of combating childhood obesity, notes Dr. Hu, because it not only affects health during childhood and adolescence, but also contributes toward earlier death in adulthood.

"The link between childhood obesity and premature death is an important public health issue," Dr. Hu said. "Prevention at early ages is an important strategy to combat this problem."