ADHD Linked to Higher Risk of Cognitive Impairment in Later Life

Experts are quick to point out that the findings don’t prove ADHD causes dementia. But seeing the same pattern show up independently, in both medical records and in people’s genes, gives scientists greater confidence that the association is not simply because of how ADHD gets diagnosed, says senior author Tharick A. Pascoal, MD, PhD, an associate professor of psychiatry and neurology at the University of Pittsburgh in Pennsylvania. “Two different kinds of evidence are pointing in the same direction,” he says.

Data Came From the U.S. ‘All of Us’ Research Program

To investigate the connection between ADHD and later cognitive health, researchers turned to the National Institute of Health’s All of Us database, an ongoing project similar to the UK Biobank. Scientists gathered health records and genetic data from about 187,000 participants who were all age 50 or older. None had cognitive impairment or dementia at the start, and about 1.6 percent (3,026 people) had an ADHD diagnosis.

Scientists searched for a connection among these conditions in two ways:

• By checking whether adults with ADHD were later diagnosed with MCI or dementia more often than neurotypical adults
• By checking whether adults with a higher genetic risk for ADHD, estimated from their DNA samples, were more likely to develop these conditions

People With ADHD Were More Likely to Be Diagnosed With Mild Cognitive Impairment or Dementia

After following participants for about 10 years, investigators found that the two groups did, in fact, develop cognitive issues at different rates. About 6.7 percent of people with ADHD were diagnosed with MCI or dementia, compared with 3.4 percent of people without ADHD — nearly double the rate.

When researchers compared people of the same age, sex, race, and ethnicity, ADHD was linked to more than four times the risk of cognitive issues. After accounting for other mental health conditions such as depression and anxiety (which were more common among the ADHD cohort), participants with ADHD had three times the risk.

This pattern also showed up in participants’ DNA: Adults who scored in the top fifth for genetic predisposition to ADHD had a 35 percent higher risk of MCI or dementia than people in the bottom fifth.

Earlier studies in Taiwan, Sweden, Israel, and Germany also found a higher risk of cognitive issues among people with ADHD, says a coauthor of the study, Douglas Teixeira Leffa, MD, PhD, a psychiatrist in Pittsburgh who recently completed his residency at the University of Pittsburgh Medical Center (UPMC).

“We’re replicating a pattern that’s been observed in other countries, now in a large U.S. sample, and adding genetic evidence on top of it,” says Dr. Leffa. “That combination gives us more confidence that ADHD deserves a closer look as a potential factor in cognitive aging,” he says.

Finally, the study also found that, among all participants who eventually developed MCI or dementia, those with ADHD had worse outcomes. Co-occurring ADHD was linked with poorer mental health, quality of life, and social satisfaction, as well as about 20 percent more healthcare visits in the following year. This pattern suggests ADHD may also shape how people experience cognitive impairment, says Leffa.

Possible Explanations for the Connection Between ADHD and Later Cognitive Issues

Researchers don’t yet know why ADHD may be tied to a higher risk of cognitive impairment, and the study wasn’t designed to find out. But Leffa says the explanation “likely involves multiple interacting processes.”

“People with ADHD may, on average, have greater lifetime exposure to factors associated with poorer cognitive health, including sleep problems, cardiometabolic risk, physical inactivity, substance use, chronic stress, and social adversity,” says Leffa.

There may also be shared biological or genetic factors behind both ADHD and later cognitive impairment, he says. The researchers statistically accounted for several potentially relevant factors, but it’s hard to pinpoint how much each contributes, he says.

Another possibility is that people with ADHD have lower cognitive reserve, or resilience, which means they may be less able to compensate for age-related brain changes caused by disease. That could result in memory or other thinking problems becoming noticeable sooner, says Leffa.

Strengths and Limitations of the Study

“The study included a large number of participants and appears well-designed,” says Richard Marottoli, MD, MPH, the medical director of the Dorothy Adler Geriatric Assessment Center at Yale–New Haven Hospital in Connecticut, and an investigator at the Yale Alzheimer’s Disease Research Center, who was not involved in the study. But because the study was observational, the results only demonstrate a correlation between ADHD and cognitive impairment, not that ADHD causes it.

It’s possible that early dementia symptoms may have been mistaken for ADHD in some cases. The link weakened when researchers required longer gaps between the two diagnoses, though it held for several years, and the authors say they can’t rule out some misattribution.

All participants were volunteers, who may not reflect everyone with ADHD. The genetic risk score calculation was based primarily on people of European ancestry, which could limit the study's relevance for people from other backgrounds. Finally, the researchers couldn’t tell whether ADHD treatment changed the risk of later cognitive issues.

How to Protect Brain Health When Living With ADHD

The study didn’t test any habits or treatments, but experts say adults with ADHD can start with steps that support brain health in general.

“At this point, we also do not have convincing evidence that a specific ADHD treatment prevents later cognitive impairment,” says Leffa. He recommends that adults with ADHD focus on the same habits that support brain health for everyone, including:

• Get regular physical activity.
• Prioritize sleep.
• Manage heart and metabolic health.
• Don’t smoke or use illicit drugs.
• Stay socially active and mentally engaged.

Midlife adults with ADHD, like their peers, should address risk factors for cognitive impairment and make sure they have a healthcare provider who can identify and treat cognitive concerns, says Dr. Marottoli.