People who are diagnosed with attention deficit hyperactivity disorder (ADHD) as adults could be at greater risk of developing dementia later in life, research suggests.
While experts cautioned that the study did not establish whether the apparent link was cause and effect, they say it highlights the need to explore possible connections further and examine whether ADHD medications mitigate any potential dementia risk.
The results come from a study of the medical records of more than 100,000 people, which found those diagnosed with ADHD as adults appear to have almost three times the risk of being diagnosed with dementia later in life.
The team behind the work say 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 at the University of Haifa.
Writing in the journal Jama Network Open, the researchers report that they studied electronic health records of the nonprofit health maintenance organisation (HMO) Meuhedet Healthcare Services in Israel. People with an existing diagnosis of ADHD or dementia were excluded from the study.
The team looked at records from 109,218 people who were on average 57.7 years old when the study began in January 2003, and tracked their records until whichever came first of death, leaving the HMO, being diagnosed with dementia or the end of the study in February 2020.
The results revealed that 730 people were diagnosed with adult ADHD over the study period, 96 (13%) of whom were also diagnosed with dementia. By contrast, there were 7,630 dementia diagnoses (7%) among those who did not receive an adult ADHD diagnosis.
After taking into account factors including age, sex, socioeconomic status, smoking and various health conditions, the team found those who were diagnosed with adult ADHD during the study had a 2.77 times greater risk of being diagnosed with dementia.
The results also suggested that ADHD medication changed the picture.
“There was no clear association between ADHD and dementia risk among those with psychostimulant medication [which is taken for ADHD] exposure,” the team write, adding that the finding required further study.
However, Levine noted that the team could not say if the results extended to childhood ADHD and that the study could not prove cause and effect.
Prof Roxana O Carare, of the University of Southampton, who was not involved in the work, also stressed the latter point, and suggested future work could explore whether the disturbances in levels of neurotransmitters in the brain seen in ADHD were linked to a higher risk in developing dementia.
However, Prof Chris Hollis, of the University of Nottingham, said there could be a number of factors muddying the waters. “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, adding that it would also be reassuring if dementia diagnosis was independently confirmed by brain imaging.
“Crucially, patients with ADHD should not be alarmed,” he said. “More research is required to substantiate this link, and, if proven, an important question would be whether ADHD treatment mitigates this potential risk.”
Henry Shelford, the chief executive of the charity ADHD UK, said a key conclusion from the work was the need to learn much more about ADHD and its secondary effects. “Right now ADHD in the UK is struggling to get proper recognition, let alone important deep research,” he said.
