Adults with attention-deficit/hyperactivity disorder (ADHD) are nearly three times more likely to develop dementia than other adults, a new study suggests.

The results also indicate that treatment with ADHD medication may help reduce their dementia risk. No clear uptick in dementia risk was found among ADHD patients who received psychostimulant medication.

“More than 3% of the adult U.S. population has ADHD, and most go undiagnosed,” said senior researcher Abraham Reichenberg, a professor of psychiatry at the Icahn School of Medicine at Mount Sinai, in New York City.

“There is limited research on this group, and it is important to determine if this group is at higher risk for dementia and if medications and/or lifestyle changes can affect risk, in order to inform caregivers and clinicians and increase awareness of this condition,” he said.

Reichenberg emphasized that the study doesn’t prove that ADHD causes dementia, only that there appears to be a link.

“If you have ADHD as an adult, you have a higher chance of dementia than someone who does not have ADHD,” he said.

Exactly why adult ADHD and dementia seem to be connected is unknown, Reichenberg noted.

“It is possible that some of the genetic causes of ADHD and the genetic causes of dementia are the same, and therefore there are similar genetic pathways to both disorders,” he suggested.

Many factors can increase dementia risk, he pointed out. Among them are diabetes, high blood pressure and lack of physical exercise. “In the context of these many risk factors, one should try to preserve both good general health and good cognitive health,” he advised.

For the study, Reichenberg and his team collected data on more than 109,000 Israelis who were born between 1933 and 1952 and followed from 2003 to 2020.

Even when other risk factors for dementia, such as heart disease, were considered, the investigators found that adults with ADHD had a significantly higher risk of dementia.

During 17 years of follow-up, 730 participants (nearly 1%) were diagnosed with ADHD, and over 7,700 (7%) with dementia.

Dementia developed in 13% of those with ADHD and in 7% of others, the findings showed.

“Adults with ADHD have a substantially increased risk for dementia,” Reichenberg said. “Symptoms of attention-deficit and hyperactivity in old age should not be ignored and should be discussed with physicians.”

One expert who was not involved with the study agreed that the link between the two could be genetic or the result of risk factors common to both conditions.

“The results of this study suggest that adult ADHD may be associated with an increased risk of dementia. Though the study population is very large, as an observational study this research is unable to establish causation,” said Claire Sexton, senior director of scientific programs and outreach at the Alzheimer’s Association.

Also, because the study was done in Israel it is not necessarily representative of the U.S. population, she said.

Several explanations might underlie a link between ADHD and dementia, Sexton said.

“For example, a range of other factors — including depression, high blood pressure, smoking, diabetes, low levels of education and physical inactivity — are associated with both dementia and ADHD, and may contribute to a relationship,” she said.

Sexton noted that a study published earlier this year found that a genetic risk for ADHD was associated with the development of amyloid-beta plaque, a hallmark of Alzheimer’s disease.

“More research is needed to replicate these findings in representative populations and to further examine possible underlying mechanisms,” she said.

The findings were published online Oct. 17 in JAMA Network Open.

More information

For more on adult ADHD, head to the U.S. National Institute of Mental Health.

SOURCES: Abraham Reichenberg, PhD, professor, psychiatry, Icahn School of Medicine at Mount Sinai, New York City; Claire Sexton, PhD, senior director of scientific programs and outreach, Alzheimer’s Association; JAMA Network Open, Oct. 17, 2023, online