Study co-author F. Xavier Castellanos, a psychiatrist at the Child Study Center at New York University Langone Medical Center in New York, and colleagues at Verona University in Italy; the Institute for Psychiatric Research in Orangeburg, N.Y.; and the Neuroingenia Clinical and Research Center in Mexico said ADHD might affect up to 11 percent of U.S. children, the majority boys.
The study involved 207 white boys with childhood ADHD -- mean age of 8.3 -- interviewed at ages 18-25 and age 41. At age 18, 178 boys without ADHD were recruited.
At 41, 111 men with childhood ADHD and 111 men without childhood ADHD self-reported their weight and height.
The study, published in the journal Pediatrics, found at age 41, the men who had ADHD weighed an average of 213 pounds, and 41 percent of them were obese, while the men who hadn't had ADHD weighed 194 pounds on average, and 22 percent were obese.
The study didn't figure out why boyhood ADHD might be causing weight problems in adulthood -- the weight gain could be caused by psychological factors or neurobiology, Castellanos told NPR.
Differences in the pathways for dopamine, a neurotransmitter in the brain, have been found in both people who are obese and people with ADHD, Castellanos said.
"It makes sense, because they're self-medicating with carbohydrates," Dr. Edward Hallowell, a psychiatrist in Sudbury, Mass., who has ADHD and treats adults with ADHD but wasn't involved with the study, told NPR. "Carbs do the same thing that stimulant medications do -- promote dopamine."