The study of more than 700,000 children found that constipation nearly tripled and fecal incontinence increased six-fold among kids with ADHD.
"We also found that children with ADHD tend to have more visits to see a doctor, suggesting that these children have more severe constipation and fecal incontinence than other children," said lead researcher Dr. Cade Nylund, an assistant professor of pediatrics at the Uniformed Services University of the Health Sciences.
Taking medication to treat ADHD did not seem to affect the number of office visits for these bowel problems, according to the study, which was published online Oct. 21 in the journal Pediatrics.
In the United States, more than 8 percent of children are diagnosed with ADHD. Kids with the condition display hyperactivity, as well as difficulty staying focused, paying attention and controlling their behavior.
These ADHD-related behavioral problems may lie behind the increased risk for bathroom woes, Nylund said.
"Kids with ADHD may not respond properly to physical cues to go to the bathroom," Nylund said. "They may have difficulty interrupting other or more desirable tasks they wish to engage in at that time."
Fecal incontinence is a more severe form of constipation, Nylund said. "What happens is, kids have constipation for several years and then they lose normal cues to go to the bathroom entirely. Then ... they just overflow and leak into their underwear."
Parents who notice that their child is suffering from constipation should see their pediatrician, Nylund said. In addition, parents can prevent constipation by increasing fiber in their child's diet, he said.
"Parents need to be aware that this risk exists and hopefully prevent constipation from occurring," Nylund said.
One expert said he sees this problem all the time among his patients -- both children and teenagers -- but it is often ignored and untreated.
"Their parents are noticing that they do have constipation, but they are not bringing it to the attention of a pediatrician or child psychiatrist, and it's going unnoticed and unaddressed," said Dr. Matthew Lorber, acting director of child and adolescent psychiatry at Lenox Hill Hospital in New York City.
Lorber said children with ADHD also might digest food more slowly or irregularly than children without ADHD. "Physiologically, that can lead to problems that cause constipation or fecal incontinence," he said.
Parents can help by setting consistent times for their child to go to the bathroom, such as before going to school or to bed, or before a long car trip, Lorber said.
He also said parents shouldn't "yell at their children for 'accidents.'"
Dr. William Muinos, associate director of pediatric gastroenterology at Miami Children's Hospital in Florida, agreed that children with ADHD often are distracted and forget to go to the bathroom.
"What we do is place them on lubrication therapy -- medication that will lubricate the bowel to help stimulate defecation," he said. "The other thing we do is simple behavior modification." This involves teaching the child to go to the bathroom at specific times, usually twice a day -- once before going to school and once in the evening, he said.
For the study, Nylund's team collected data on nearly 750,000 children, aged 4 to 12 years, who had a parent on active military duty. Among these children, nearly 33,000 were identified as having ADHD.
The researchers found that 4.1 percent of the children with ADHD suffered from constipation, compared with 1.5 percent of children without the condition.
In addition, 0.9 percent of the children with ADHD suffered from fecal incontinence, compared with 0.15 percent of children without ADHD.
Even when adjusted for factors such as age, gender and birth order, the researchers found the risk for fecal incontinence was more than six times greater among kids with ADHD and the risk for constipation was almost three times higher.
Although the research showed an association between ADHD and increased instances of constipation and incontinence, it did not prove a cause-and-effect relationship.
For more information on ADHD, visit the U.S. National Institute of Mental Health.