A new study suggests that children who have attention-deficit/hyperactivity disorder (ADHD) may be at a higher risk of becoming obese as teenagers.

There have been previous studies associating ADHD with obesity, but what exactly explains the relationship has remained unclear, as has whether additional weight or behavioral problems come first.

"In general, people think of children with hyperactivity as moving around a lot and therefore should be slim," senior author Alina Rodriguez said.

But Rodriguez said that children who have ADHD tend to be overactive in a fidgety way.

"Children with ADHD are not more likely to participate in physical activity, as we show in our report," she said.

The team's study suggests that kids with behavioral problems are less likely to be active as they age.

For their study, the researchers examined almost 7,000 children in Finland to determine whether ADHD symptoms at age eight were linked to greater chances of being obese by age 16. They interviewed parents and teachers of the children to determine their ADHD symptoms and conduct disorder symptoms at the ages of eight and 16.

The results of the study showed that children who had ADHD symptoms at a young age were nearly twice as likely to be obese as teens. This was true even after taking into account childhood weight.

"Obesity is a growing problem that we need to watch out for in all children and young people, but these findings suggest that it's particularly important for children with ADHD," Rodriguez said. "It appears that lack of physical activity might be a key factor. We think encouraging children with ADHD to be more physically active could improve their behavior problems as well as helping them to stay a healthy weight, and studies should be carried out to test this theory."

According to the American Psychiatric Association, about five percent of U.S. kids have ADHD, a condition that usually involves difficulty paying attention and lack of impulse control. There is no cure for the condition, but treatment through a combination of medication and behavior therapy exists, according to the Centers for Disease Control and Prevention.

According to Doctor L. Eugene Arnold, child psychiatrist and professor emeritus at The Ohio State University in Columbus, parents of children with ADHD should encourage active pursuits and join their children in being active if necessary. They should also limit screen time and keep health snacks available to prevent adolescent weight problems.

The results of the study were published in the Journal of the American Academy of Child and Adolescent Psychiatry.