Identification and treatment issues surrounding attention deficit hyperactivity disorder (ADHD) are challenging enough. Now research is shedding light on long-term outcomes for people with ADHD. A May 20 study in Pediatrics reports that men who had ADHD in childhood are twice as likely to be obese in middle age, even if they no longer exhibit symptoms of the disorder.

ADHD is a mental disorder characterized by hyperactivity, impulsivity, inattention and inability to focus. It affects approximately 6.8 percent of U.S. children ages three to 17 in any given year, according to a recent report by the U.S. Centers for Disease Control. Medications used to treat ADHD, such as Ritalin (methylphenidate) or Adderall (dextroamphetamine and amphetamine), are stimulants that can suppress appetite. Two recent retrospective studies, however, have pointed to a possible increased risk for obesity among adults diagnosed with ADHD as children.

The new 33-year prospective study started with 207 healthy middle-class white boys from New York City between six and 12 years old, who had been diagnosed with ADHD. When the cohort reached an average age of 18, another 178 healthy boys without ADHD were recruited for comparison. At the most recent follow-up when the participants were an average age of 41, a total of 222 men remained in the study.

A troubling pattern emerged: A comparison of the men’s self-reported height and weight revealed obesity in twice as many men who had childhood ADHD were obese as in those without the disorder. The average body mass index (BMI) of the men with childhood ADHD was 30.1, and 41.4 percent were obese whereas those without the condition as kids reported an average BMI of 27.6 and an obesity rate of 21.6 percent. The association held even after the researchers controlled for socioeconomic status, depression, anxiety and substance abuse disorders.

The results have implications for parents currently raising kids with ADHD. “Many parents are concerned that their children may not be gaining as much weight as they should because [ADHD] medications can decrease appetite in the short run, but these results would lead me to be much less worried about that now,” says corresponding author F. Xavier Castellanos of the Phyllis Green and Randolph Cowen Institute of Pediatric Neuroscience at New York University Langone Medical Center. “It helps us to realize that over the long run, the potential risks of obesity, of overeating and of dysregulation, are a more prominent long-term concern."

The study is case-controlled, which means researchers identified participants (cases) with the condition and then matched them to a control population to compare outcomes and look for risk factor differences. Therefore, it cannot prove causation because it’s observational. Only a randomized, controlled trial could show that obesity is caused by ADHD—but it’s impossible to randomize participants to have ADHD, both because it is unethical and researchers do not know precisely what brings about the condition. Possible causes could include genetics, nutrition, environmental factors or brain injuries.

Despite these shortcomings, the study’s findings are similar to results in other research that has found links between ADHD and obesity. The previous studies, however, were retrospective (relying on participants’ recall), did not focus exclusively on ADHD (included other conduct disorders) or compared only men suffering from adult ADHD with those having remitted childhood ADHD, rather than to controls without ADHD. This prospective study is the most long-term and the first to focus exclusively on adult obesity rates in men with childhood ADHD compared with those who did not have the condition as children. Its findings therefore contribute to the growing evidence base for an association between obesity and childhood ADHD.

An unclear mechanism

A link between obesity and childhood ADHD could be explained by either a neurobiological or a psychological mechanism, the authors proposed. With the former it is possible that something similar genetically underlies both ADHD and obesity; Castellanos and his colleagues note that dysfunction in the dopamine pathways of the brain have been found among both people who are obese and those with ADHD. As for the psychological mechanism, the impulsive behaviors and diminished inhibitions associated with ADHD “may foster poor planning and difficulty in monitoring eating behaviors, leading to abnormal eating patterns and consequent obesity,” the team wrote.

“One of the aspects of ADHD is this tendency to focus on ‘I want it now’ and not waiting for something, not delaying gratification, so we think that may lead people to eat more than they physiologically might need,” Castellanos says. Eating just an extra 100 calories a day than the total burned can easily lead one to accumulate extra pounds. Appetite regulation is complex but usually balances out in healthy individuals—unless they eat when they’re not actually hungry.

Some researchers are dubious about both the neurobiological and the psychological explanations. Lawrence Diller, a behavioral developmental pediatrician at the University of California, San Francisco (U.C.S.F.), and author of Remembering Ritalin and Running on Ritalin, says he finds the idea of dysregulation in adulthood unlikely for adults who no longer have symptoms of ADHD. “The finding is real—no question about it—but the explanations are poor,” Diller says. “If the ADHD is remitted, then why should the impulsivity and poor judgment still be there?”

Of the 111 men with childhood ADHD in this study, 87 no longer had ADHD symptoms (remitted) and 24 still had ADHD (persistent). Those with remitted ADHD had relatively higher obesity rates than the persistent-ADHD men, although the small number of men with persistent ADHD makes it difficult to draw any substantial conclusions about this difference.

Diller suggested that the long-term impact of ADHD medication may play a part. “We know that stimulants very much affect the satiety thermostat in people who take them,” he says. “There is the question of whether or not the long-term suppression of appetite somehow affects the brain so that when you’re no longer taking the drugs, it takes more [food] to make you feel full.” Diller pointed to research showing that long-term use of ADHD stimulants can lead to 2.5 to five centimeters of lower-than-predicted height in adults, although the adults in this new study showed no significant differences in height. “That doesn’t mean you shouldn’t take the medicine, but in weighing the pros and cons, it’s one more thing for parents to think about in treatment,” Diller says. “The idea that impulsivity and poor judgment may play a role is possible, but I think my idea of adjusting the satiety thermostat long-term is just as plausible as theirs.”

A different possible mechanism, proposed by Juan Salinas, a lecturer specializing in the neuropharmacology of learning and memory at the University of Texas at Austin, resembles the neurobiological hypothesis, given that ADHD involves a dysfunctional release of dopamine in the brain. “From more basic research into the neurobiology of reward, it’s suggestive that maybe somehow these people who do not have ADHD anymore may have an alteration in the dopamine pathways, and maybe some of the eating may be a way to self-medicate to increase dopamine release,” Salinas says. “It’s not so much impulse control, but it’s a self-medicating idea.” The implications of the study, then, Salinas says, are that parents need to train their children with ADHD early to eat healthily, exercise and practice a healthy lifestyle.

Another line of thought, proposed by Stephen Hinshaw, a psychology professor specializing in ADHD at U.C.S.F. and U.C. Berkeley, extends the poor impulse control hypothesis. “It’s plausible that there are biological underpinnings of both ADHD and obesity,” he says, “but the more parsimonious explanation from other research is that ADHD portends problems in self-regulation over time.” In other words, adults who once had ADHD might later be able to sit in a chair and refrain from fidgeting, but emotional and physical regulation issues could linger in the form of less-than-ideal eating habits.

“Devastating” long-term consequences

Hinshaw’s own work with ADHD in girls and other research into long-term outcomes support this idea that the challenges of self-regulation may not fade when the outwardly clinical symptoms of hyperactivity do. His 10-year study of 140 young adult girls who had childhood ADHD found much higher rates of self-cutting, self-burning and suicide attempts in this group than were found in a control group.

Additionally, he says, recent research has found high levels of unemployment and underemployment as well as poorer work productivity among adults who had childhood ADHD than among those who did not. The men with childhood ADHD in the new study also had significantly lower socioeconomic status than did those in the control group, even though the groups had been matched initially for parental socioeconomic status and geography. “ADHD still gets ridiculed in the press—saying it’s a made-up disease or that we just don’t tolerate fidgety kids—but it has really devastating long-term consequences, and we have to take it seriously,” Hinshaw says.

Rising rates of ADHD diagnoses could be related to both improved health care access for more children and possible misdiagnoses due to the inadequate time spent on assessments in pediatricians’ offices. “We need to insist upon a much higher level of diagnosis and evaluation so that we’re really sure that it’s ADHD and not maltreatment or family conflict or normal-range behavior,” Hinshaw says. For those who really suffer from ADHD, this study provides more evidence of the challenges those children will face in adulthood. “ADHD has staying power,” he says, “regardless of whether the symptoms on the surface improve or not.”