Young women who were diagnosed with attention-deficit hyperactivity disorder (ADHD) in childhood are more likely to be obese than peers without an ADHD diagnosis, according to a U.S. study.

The results don't prove cause and effect, but some of the symptoms of ADHD, like impulsiveness and difficulty focusing might contribute to an inability to stick to healthy eating habits, even in adulthood, the researchers speculate.

"Several cross-sectional studies have suggested an association between childhood ADHD and obesity," said study author Dr. Seema Kumar, a pediatrician and researcher at Mayo Clinic Children's Research Center in Rochester, Minnesota.

She and her colleagues analyzed data on 336 adults with childhood diagnoses of ADHD and 665 similar people without an ADHD diagnosis. All were born between 1976 and 1982 and their medical records included their heights, weights and medication regimens between 1976 and 2010.

More than 34 percent of people with childhood ADHD were obese after age 20 compared to 25 percent of those without ADHD, researchers found. But the difference was only statistically significant - meaning it was too big to be due to chance - among the women.

Participants who were not obese when ADHD was first diagnosed were about 50 percent more likely to be obese in later years than people in the comparison group without ADHD, but again, the increased risk held true only for female participants.

There may be shared underlying abnormalities in the neural pathways that mediate not only impulse control and reward sensitivity in ADHD but also appetite and satiety, Kumar told Reuters Health by email.

Poor decision-making in individuals with ADHD may lead to disordered eating, she said.

"Sleep difficulties, often present in children with ADHD, may also lead to excess weight gain due to a combination of behavioral and hormonal factors," she said.

"Our finding of sex-specific differences in the association between ADHD and obesity may be related to some extent to unique differences in the subtypes of ADHD seen in females compared to males," she said. "Females have a higher prevalence of the inattentive subtype of ADHD while males have a higher prevalence of the hyperactive/impulsive subtype, a subtype that may be associated with a higher energy expenditure and therefore protective against weight gain."

Stimulant treatment was not related to obesity risk, the study team notes in Mayo Clinic Proceedings.

"It is important to know that in our study, stimulants had been used for only a fraction of a patient's life, ranging between one and a half years to six years," Kumar said. "It is not known if longer duration of stimulant treatment may alter the risk of obesity," she cautioned.

"Parents and doctors should encourage healthy eating and active lifestyle in all patients with ADHD," Kumar said. "Additionally, weight monitoring should be incorporated as part of routine care of all patients with ADHD so that excess weight can be detected early and that efforts to prevent further weight gain can be instituted in a timely fashion."

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