Increased risk of dementia in adults with ADHD

Much of the research on attention deficit/hyperactivity disorder (ADHD) focuses on the challenges — and potential benefits — of living with the condition as a child, or as an adult who has grown up with ADHD. But ADHD can also develop later in life. Though adult ADHD is distinct in various ways from childhood ADHD, little is known about it. 

Now, a study in JAMA Network Open of more than 100,000 older adults has revealed a worrying implication: a diagnosis of adult ADHD was associated with a nearly three times greater risk of developing dementia, including Alzheimer's disease. 

Stephen Z. Levine at the University of Haifa, and colleagues studied 109,218 Israelis who were enrolled with a healthcare services organisation and who were aged between 51 and 70 at the start of the study period, in 2003. At this point, none had a diagnosis of adult ADHD or dementia. The team analysed their medical records through to 2020, when their average age was 75.5. 

The researchers found that 730 participants (0.7% of the total) were diagnosed (by a psychiatrist, neurologist or clinical neuropsychologist) with ADHD during the 17.2 year period before follow-up. During this time, 13.2% of these people also received a dementia diagnosis, compared with 7% of those without adult ADHD. Overall, participants with adult ADHD were 2.77 times more likely than those without it to go on to be diagnosed with a form of dementia. This association held even when the team controlled for a variety of other factors known to be involved in the risk of developing dementia, such as the presence of cardiovascular disease or depression, and socioeconomic status. 

Exactly what causes adult ADHD and how precisely it differs from childhood ADHD is not well understood. Perhaps adult ADHD reflects a pathobiological brain process that reduces a person's ability to compensate for the effects of neurodegeneration in later life, the researchers suggest. This reduced ability to compensate may then make it more likely that they will display the signs of dementia, and receive a diagnosis. 

The team's analysis also revealed something else, however. The 22.3% of participants diagnosed with adult ADHD who took prescription psychostimulants for the disorder had the same, lower dementia risk as participants without adult ADHD. 

Other research has found that methylphenidate (which is sold under the brand name Ritalin), a stimulant commonly used to treat ADHD, can treat cognitive impairment in people diagnosed with Alzheimer's disease. Perhaps, then, psychostimulants might counteract the increased risk of dementia for people with adult ADHD. However, further research is necessary to examine the impacts of these drugs on older people, the team cautions. "There are multiple risks and benefits to weigh before considering psychostimulant medication as a dementia prevention strategy," they write. 

As with any study, there were some limitations to this research. One is that they didn't have any information about diagnoses of childhood ADHD for these participants. However, they stress that as research suggests that childhood ADHD and adult ADHD are distinct, their findings should only be taken to be relevant for adult ADHD. Another limitation is that, although they took various other factors that influence dementia risk into account, they did not have data on the participants' lifelong academic achievement or likely cognitive reserve.

Despite these limitations, this new finding does suggest that if an older adult develops symptoms of ADHD, this is something that they or a family member or caregiver should raise with a doctor. Given the implications for the individual of a diagnosis of dementia, as well as the increasing global burden of caring for people with these conditions, further work on whether psychostimulants can safely reduce the risk of dementia for people with adult ADHD — if not also more broadly — is clearly needed urgently.

Read the paper in full: https:doi.org/10.1001/jamanetworkopen.2023.38088