Young adults with a history of symptoms of attention-deficit hyperactivity disorder (ADHD) may be more likely than their peers to be obese, a new study suggests.

The findings, from a study of more than 11,000 young U.S. adults followed since adolescence, do not prove that ADHD by itself raises the risk of obesity. But they are in line with a number of smaller, previous studies finding that both children and adults with ADHD have a higher obesity rate than those without the disorder.

The reasons are not yet certain. But it’s biologically plausible, researchers say, that the impulsive behavior that commonly marks ADHD would be related to excess weight gain.

According to the Centers for Disease Control and Prevention, between three and seven percent of school-aged kids in the U.S. suffer from ADHD.

In the new study, researchers at Duke University in Durham, North Carolina, examined data from 11,666 young U.S. adults taking part in a government health study begun in 1995, when the participants were in high school.

In 2001-2002, when participants were age 23, on average, they were surveyed on whether they’d had various ADHD-like symptoms between the ages of five and 12. They were followed up again six to seven years later, when their weight and other health and lifestyle factors were recorded.

Overall, the researchers found, young adults who said they’d had three or more ADHD-like symptoms during childhood had a higher rate of obesity than those who reported no such symptoms.

A history of hyperactivity or impulsive behavior - as opposed to problems with attention - was particularly related to obesity.

Of study participants who, in their early 20s, reported a childhood history of three or more hyperactivity/impulsivity symptoms, 41 percent were obese six to seven years later. That compared with a rate of 34 percent among those who reported no such childhood symptoms.

When the researchers accounted for a number of other factors - including participants’ current exercise levels, reported history of depression and smoking habits - a history of three or more hyperactivity/impulsivity symptoms was linked to a 50-percent increase in the odds of adulthood obesity.

The link between inattention-type symptoms and obesity was weaker, and only hyperactivity and impulsivity were related to changes in body weight from adolescence to young adulthood.

The results, reported in the International Journal of Obesity, do not prove that ADHD causes weight gain. It’s possible that other things about adults with a history of ADHD could have led to the extra pounds.

Still, there are reasons to believe that ADHD itself could be connected to obesity risk, according to lead researcher Dr. Bernard Fuemmeler, director of the pediatric psychology and family health promotion lab at Duke.

“Hyperactivity and impulsive symptoms seem to be driving this relationship,” Fuemmeler said in an interview. So it’s possible, he explained, that problems with impulse control ultimately affect some people’s weight.

“Do people with these symptoms have a more difficult time stopping themselves from having that second helping?” Fuemmeler said. “Do they have a more difficult time making decisions about whether to get a ‘reward’ now or put it off to later?”

In addition, both ADHD and eating behavior are believed to be related to the brain’s dopamine system. Fuemmeler said that points to a potential biological pathway connecting the disorder and weight control.

The study, which was funded by the government, has a number of limitations, including its reliance on participants’ recollection of past ADHD-like symptoms. The researchers did not have information on actual diagnoses of the disorder.

But using symptoms instead of a diagnosis allowed Fuemmeler’s team to look at the level of reported symptoms and the odds of obesity. They found that the greater the number of childhood symptoms, the higher the odds of adulthood obesity.

“This tells us that this relationship might be important, and deserves further study,” Fuemmeler said.

For now, he said, teenagers and young adults with a history of ADHD can be aware of the potential link to weight gain and, as is recommended for everyone, be mindful of their diets and lifestyle habits.

Fuemmeler also noted that a concern with giving ADHD medications to children is the fact that the drugs can dampen appetite and, therefore, could hinder their growth. But, he said, when teenagers and young adults stop using the medications, they may want to be careful that they do not begin overeating.

Fuemmeler also suggested that anyone with a history of impulsive behavior - even in the absence of formal ADHD diagnosis - take simple measures to keep their diets on track.

“Try restructuring your environment so that you’re not surrounded by things that tempt you,” he said. “If you know you’re on the impulsive side, avoid driving by that fast-food restaurant.”

Two co-researchers on the work have received consulting fees or research support from drug companies that make ADHD medications.

SOURCE: International Journal of Obesity, online October 26, 2010.