Nearly a third of people diagnosed as children with attention deficit hyperactivity disorder (ADHD) still have the condition in adulthood, according to a U.S. study of thousands.
The researchers, whose findings appeared in Pediatrics, also found that these people were more likely to develop other mental disorders, such as anxiety or depression, and commit suicide.
Lead by William Barbaresi from Boston Children's Hospital, they found that about 29 percent of participants in the study who were diagnosed with ADHD as children ended up carrying that diagnosis over into their late twenties.
"They still clearly had symptoms that continued to be consistent with that diagnosis," said Barbaresi. "But that in itself has been an area of difficulty and controversy."
ADHD, the most common neuro-developmental condition, affects between 3 percent and 7 percent of U.S. school children, according to the U.S. Centers for Disease Control and Prevention (CDC). It's more common in boys than in girls.
The CDC says children with ADHD tend to have a hard time paying attention, to be forgetful, fidget and be easily distracted, to the point that it creates problems at school, home and with their friends.
For their study - which Barbaresi started while at the Mayo Clinic in Rochester, Minnesota - the researchers followed 5,718 children who were born in that area between 1976 and 1982. Of those, 387 were diagnosed with ADHD as children and gave the researchers access to their medical records.
Barbaresi and his colleagues then invited the participants to be re-evaluated when they were 29. Overall, 232 of the childhood ADHD patients agreed to take part, and the researchers found that 68 still had the disorder - around 29 percent.
But even those whose ADHD diagnosis did not persist into adulthood were still more likely to suffer from at least one psychiatric condition other than ADHD, with at least 57 percent suffering with such things as alcohol or substance abuse, anxiety or depression.
That compared to 35 percent of the people in a comparison group who did not have ADHD while growing up.
People diagnosed with ADHD were also more likely to commit suicide. Researchers found that 3 of the 387 participants with childhood ADHD had committed suicide, compared to just 7 of the 4,946 non-ADHD participants.
"The finding about suicide is new," said Mary Solanto, director of the ADHD Center at the Icahn School of Medicine at Mount Sinai in New York. "It was suggested in another one of these ... studies, but in this study the sample size was large enough for it to be significant."
Solanto, who was not involved in the new research, said that many of the study's other findings had been seen previously, but that this study was larger and the subjects were drawn from the general population.
The study's authors warned that their findings may not apply to children across the United States because the study participants were from mostly white, middle-class families in one part of Minnesota.
"There are a lot of people who have had it (ADHD) that learned to cope and deal with it," Solanto said. "But in order for that to happen, it's important to diagnose and treat it as soon as possible."