A major shift in the way researchers and clinicians look at attention deficit hyperactivity disorder (ADHD) may be on the horizon, according to two new studies that each tracked thousands of people for almost 20 years after birth. One group was in the United Kingdom while the other was in Brazil, but the findings from both, published in JAMA Psychiatry, were remarkably similar in two ways: Both found that a significant proportion of adults with ADHD did not have the condition as children, and the majority of those adults were women.
Or, more plainly: It seems lots of women who didn’t have ADHD in childhood are now being diagnosed as adults. What that means, however, isn’t so simple: Scientists don’t really know yet, but they have a few ideas.
The UK study followed 2,040 adults from birth, during 1994 to 1995, through age 18. Over that time, researchers assessed the children for ADHD at ages 5, 7, 10 and 12 and found the overall 12% of them with ADHD fairly evenly distributed across those ages, though tilting a little heavier on the earlier ages. But when they assessed the group at age 18, the numbers had shifted quite a bit, and only one of every five kids with ADHD still had it as adults.
In the overall population, 2.6% had ADHD as both children and adults, whereas 9.5% had it in childhood but no longer met the diagnosis criteria as young adults. Meanwhile, a completely separate 5.5% of all the participants had ADHD in adulthood but not in childhood. And the proportion of males and females had flipped. Among the children with ADHD, 73% were boys, but only 45% of those newly diagnosed as adults were men.
So what’s happening here? The authors of the study suggest three possibilities. First, it may be that the adults diagnosed for the first time with ADHD had the susceptibility for the condition all along, but the disorder might have been “masked in childhood owing to protective factors, such as particularly supportive family environments or highly developed cognitive skills.”
One bit of evidence supporting this possibility was that, as a group, the children with ADHD who continued to have it in adulthood tended to have worse symptoms and slightly more likely to have a lower IQ, though only by a few points. Those diagnosed only as adults, however, were a bit more likely to have a higher IQ and fewer behavioral problems. That suggests that the ADHD diagnosis was missed in those adults because they were a bit smarter and didn’t act out as much. “In such cases,” the authors write, “symptoms may not become impairing until the increasing challenges of later, more demanding schooling.”
Once they reach adulthood, however, those with ADHD—whether they had it as kids or not—had similar problems in daily life. They were several times more likely to have difficulties with school or work and even more likely to have trouble with their relationships with friends and family. Their odds of generalized anxiety disorder were five times greater than those who never had ADHD, and they were more likely to have a behavioral problem and dependence on marijuana.
The idea that ADHD was simply missed in these folks also squares with the differences found between the sexes. “In girls,” the authors wrote, “ADHD symptoms may be less likely to come to the attention of parents and teachers owing to lower rates of externalizing-type [outward] behaviors, resulting in fewer girls with ADHD diagnosed in childhood.” That possibility matches up with the increasing trend of adult women receiving the diagnosis.
But there are two other possibilities, these authors suggest. They might have a different disorder altogether misdiagnosed as ADHD (especially given their higher rates of anxiety, depression and marijuana and alcohol dependence) or there could be an adult version of ADHD that researchers have not yet discovered.
This second hypothesis is where the authors of the other study, from Brazil, place their bets. As in the first study, the researchers followed kids from birth in 1993 through ages 18 and 19. They assessed each of the 5,249 children in the study for ADHD at age 11 and then again at age 18 or 19. In this group, 8.9% of the 11-year-olds had ADHD (and again, not quite one in five still had it in adulthood), but 12.2% had it as adults and not as children. (One requirement for adult ADHD is that they had it as children, so the researchers eliminated this criterion for the sake of the study.)
And, once again, more of the kids with ADHD were boys while more of the adults with ADHD were women. Although the Brazilian study found that all the adults with ADHD had slightly lower IQs than the rest of the study group, it also found—as in the UK study—that those with adult-only diagnoses had a higher IQ within the ADHD group overall.
There are some caveats to keep in mind with both studies. The children’s diagnoses were based on reports from parents and teachers whereas the adult diagnoses were based on self-reported symptoms from the participants. Both methods used standard screening or testing instruments, but the difference in who is providing the information could definitely add some bias to the results. Still, both studies find a substantial number of people not receiving an ADHD diagnosis until they’re adults—most of whom are women. Since the way symptoms occur in women differ from those in men, the idea that ADHD was simply missed in childhood makes sense.
It’s also very similar what Stephen Faraone, PhD, of SUNY Upstate Medical University in Syracuse, N.Y., and Joseph Biederman, MD, of Harvard Medical School in Mass., propose in their hypothesis in an accompanying editorial—“the existence of subthreshold childhood ADHD,” or ADHD that falls just barely short of the symptoms required for a proper diagnosis.
“In subthreshold cases, the onset of symptoms and impairment could be separated by many years, particularly among individuals with strong intellectual abilities and those living in supportive, well-structured childhood environments,” they wrote, echoing the authors of the UK study. “Such intellectual and social scaffolding would help youth with ADHD to compensate in early life, only to decompensated into a full ADHD syndrome when the scaffolding is removed.”
Or: It may not be tough enough as a kid if you’re smart and have a great support network of family and teachers. But when you grow up and life gets real, ADHD rears its ugly head and bites you in the butt.
Whatever the case, adulthood ADHD is clearly real, Faraone and Biederman said. It could still be a neurodevelopment disorder wired into the brain that just doesn’t show up until later in some people, or it could be an entirely different beast, but adults showing the symptoms need treatment, the UK authors said, even if they didn’t have an ADHD diagnosis as children.
