Link between adult diagnosis of ADHD and dementia, study finds

People who receive a diagnosis of attention deficit hyperactivity disorder (ADHD) as adults could be at greater risk of developing dementia later in life, according to a new study.

Researchers at the University of Haifa in Israel looked at the medical records of 109,218 people belonging to Meuhedet Healthcare Services, an Israeli nonprofit health maintenance organisation. The patients had an average age of 57.7 when the study began in January 2003, and the researchers tracked them either until they died, or they left the organisation, or they were diagnosed with dementia, or to the end of the study in 2020, depending on which came first.

The analysis, published in the journal Jama Network Open, showed that that 730 people were diagnosed with adult ADHD over the study period, 96 (13%) of whom were also diagnosed with dementia. In comparison, there were 7,630 dementia diagnoses (7%) among those who did not receive an adult ADHD diagnosis, equating to a 2.77 times greater risk. The team took into account factors such as age, sex, socioeconomic status, smoking and certain health conditions.

The research team say that the processes involved in adult ADHD may reduce the ability of the brain to compensate for the effects of processes that can happen later in life, including neurodegeneration or blood flow in the brain.

“This is consistent with the primary result that adult ADHD increases dementia risk, and mild evidence of reverse causation,” said Dr Stephen Levine, the first author of the study.

Not clear whether link is causal

The results also suggested that outcomes were different when individuals were taking ADHD medication. “There was no clear association between ADHD and dementia risk among those with psychostimulant medication [which is taken for ADHD] exposure,” the authors write.

It was also not clear whether the relationships between ADHD was a causal one, and the researchers do not yet know whether the results applied to people diagnosed with ADHD as children.

Prof Chris Hollis, of the University of Nottingham, told the Guardian there could be other reasons for the relationship between ADHD and dementia. “Those adults who seek and receive an ADHD diagnosis are also more likely to be assessed for other cognitive/neuropsychiatric conditions including dementia,” he said. He added that it would also be reassuring if dementia diagnosis was independently confirmed by brain imaging.

Average waiting time for referral is three years

The number of people with an ADHD diagnosis is growing. An investigation carried out by ADHD with ADHD UK has found that the average waiting time a referral is three years.

The longest waits for children are in Belfast (up to five years), while in Herefordshire and Worcestershire, adults can wait more than ten years for a referral.

The investigation found that only 21% of healthcare boards were able to provide their referral data. The majority were unable to indicate the length of their waiting list or how many people were on it. ITV’s freedom of information request showed there are about 26,000 people in the UK waiting for an ADHD assessment, but ADHD UK says the number should be around 110,000.

ITV spoke to a mother, Harriet, whose daughter was waiting to be seen for an ADHD diagnosis. She said: “It took us three years to get on the waiting list, then another three years to get seen. So who knows, maybe another three years, maybe we look at it in nine years. By the time she’s got a diagnosis, I really don’t know.”