These important findings may improve treatment of ADHD in adulthood, says one expert.
Adult ADHD more than doubles the likelihood of developing dementia, but psychostimulant medication negates the increased risk.
To date, research studies linking adult ADHD and dementia have been few and far between, and the outcomes conflicting.
âADHD and dementia are two conditions with high personal, social and economic cost. If ADHD proves to be a risk factor for dementia, early recognition and treatment of ADHD could alter that risk and improve quality of life [as people age],â said Dr Karuppiah Jagadheesan, chair of the Royal Australian and New Zealand College of Psychiatristsâ ADHD network committee.
Now, a recent prospective birth cohort study of more than 100,000 Israelis, published in JAMA Network Open, provides possibly the strongest evidence yet that adult ADHD increases the risk of developing dementia later in life.
More than 700 participants had adult ADHD, and the researchers found that one in eight developed dementia over the 17-year follow-up period, compared with one in 14 neurotypical individuals. This was a 2.8-fold increase in dementia risk after accounting for relevant factors such as age, sex, socioeconomic status and comorbid conditions.
Adult ADHD may reduce the ability to compensate for age-related neurodegeneration and cerebrovascular changes.
âLess cognitive and brain reserve may result in pathobiological processes of ADHD that, in turn, reduce compensatory abilities,â the authors concluded.
The good news was that psychostimulant drugs appeared to be protective against dementia.
Complementary analyses revealed no increased risk of dementia among adult ADHD patients who took the medication, while those who didnât were 3.1 times more likely to develop dementia than the general population.
âIt 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,â they wrote.
âAlso, ADHD is a chronic condition and may have negative long-term sequelae when untreated.â
Professor Kaarin Anstey, senior principal research scientist at NeuRA and director of the UNSW Ageing Futures Institute, provided an alternative explanation.
âIf ADHD is associated with dementia via comorbid mental health problems and poorer health behaviour, maybe the medication has an indirect effect on dementia risk by normalising mood and cognition so people with ADHD can better manage their lives and have fewer comorbidities,â she told TMR.
Dr Jagadheesan felt the interesting findings required further clarification before they would change clinical practice, telling TMR the study used broad definitions of dementia and psychostimulant medication use.
âPrevious studies suggest the risk is much higher for specific types of dementia [such as] Lewy body dementia or vascular dementia,â he said, noting the current study did not differentiate between different types of dementia â instead using a broader set of diagnoses.
â[And] when we talk about psychostimulant medications like dexamphetamine and methylphenidate, we have short-acting and long-acting [treatments] which needs to be considered. The dose and duration of the treatment also needs to be characterised. We also have non-stimulant medications, which are safer for certain populations,â he said.
