Teens who were depressed as children are more likely to be obese, to smoke and to be sedentary, a new study finds.

The findings suggest that depression during childhood can increase the risk of heart problems later in life, according to the researchers.

The study included more than 500 children who were followed from ages 9 to 16. There were three groups: those diagnosed with depression as children, their depression-free siblings and a control group of unrelated youngsters with no history of depression.

Twenty-two percent of the kids who were depressed at age 9 were obese at age 16, the study found.

"Only 17 percent of their siblings were obese, and the obesity rate was 11 percent in the unrelated children who never had been depressed," study first author Robert Carney, a professor of psychiatry at Washington University School of Medicine in St. Louis, said in a university news release.

The researchers found similar patterns when they looked at smoking and physical activity.

"A third of those who were depressed as children had become daily smokers, compared to 13 percent of their nondepressed siblings and only 2.5 percent of the control group," Carney said.

Teens who had been depressed as children were the least physically active, their siblings were a bit more active and those in the control group were the most active, according to the study, which is scheduled for presentation Friday at the annual meeting of the American Psychosomatic Society in Miami. Although the study showed an association between childhood depression and obesity, smoking habits and inactivity later in life, it did not prove a cause-and-effect relationship.

These findings are cause for concern because "a number of recent studies have shown that when adolescents have these cardiac risk factors, they're much more likely to develop heart disease as adults and even to have a shorter lifespan," Carney said.

"Active smokers as adolescents are twice as likely to die by the age of 55 than nonsmokers, and we see similar risks with obesity, so finding this link between childhood depression and these risk factors suggests that we need to very closely monitor young people who have been depressed," he said.

Data and conclusions presented at meetings are typically considered preliminary until published in a peer-reviewed medical journal.