Adult ADHD spells increased dementia risk

Adults with attention-deficit/hyperactivity disorder (ADHD) face a nearly threefold higher risk of dementia compared with those who do not have the neurodevelopmental condition, according to a study.

In a cohort of 109,218 older adults (mean age 57.7 years, 51.7 percent women) in Israel, having ADHD as an adult was associated with a significantly increased risk of developing dementia both in unadjusted (hazard ratio [HR], 3.62, 95 percent confidence interval [CI], 2.92–4.49; p<0.001) and adjusted (HR, 2.77, 95 percent CI, 2.11–3.63; p<0.001) analyses. [JAMA Netw Open  2023;6:e2338088]

This finding was consistent with 12 of the 14 complementary analyses that the investigators conducted. There was mild evidence of reverse causation. However, no clear association was seen between adult ADHD and dementia among participants with ADHD who received psychostimulant medications.

The study population was followed up to 17.2 years, during which 730 participants (0.7 percent) received a diagnosis of adult ADHD and 7,726 (7.1 percent) received a diagnosis of dementia. The incidence of dementia was higher among participants with vs without ADHD (13.2 percent vs 7.0 percent).

“The present study finding that adult ADHD is associated with a higher dementia risk is consistent with most, but not all, prior epidemiologic studies,” the investigators said. [J Atten Disord 2019;23:995-1006; Neurochem Int 2018;112:255-258; Eur Psychiatry 2021;65:1-19; J Aging Res 2011;2011:729801]

“It may be plausible that adult ADHD reflects a brain pathobiological process that reduces the ability to compensate for the effects of later-life neurodegenerative and cerebrovascular processes. Less cognitive and brain reserve may result in pathobiological processes of ADHD that, in turn, reduce compensatory abilities,” they explained.

As for the absence of a clear risk increase for dementia among adults with ADHD receiving treatment with psychostimulants, the investigators laid out different interpretations.

“It is possible that ADHD treated with medication reflects more severe ADHD compared with ADHD not treated with prescribed psychostimulants, which may reflect milder symptoms or even a less accurate diagnosis. Also, ADHD is a chronic condition and may have negative long-term sequelae when untreated. Hence, the lack of association among individuals exposed to psychostimulants contradicts the conclusion that ADHD is associated with dementia risk,” they said.

The investigators also pointed out that psychostimulants are cognitive enhancers and that there is some evidence to suggest that such medications may reduce dementia risk. This suggests that the association between adult ADHD and dementia risk might be confounded by psychostimulant use. [Pharmacopsychiatry 2020;53:109-114]

“That said, future research is necessary, including the assessment of adult ADHD symptom severity, to examine the role of psychostimulant medication in old age,” according to the investigators.

In the meantime, “policymakers, caregivers, patients, and clinicians may wish to monitor reliably for ADHD in old age,” they added.