The 22million Americans with attention-deficit/hyperactivity disorder could be more likely to develop early-onset dementia, a preliminary study suggests.

Researchers at the University of Pittsburgh analyzed health records from people diagnosed with ADHD as children in the 1980s and 90s.

These patients were then followed into adulthood and are now in their 40s. 

They found adults living with ADHD scored worse on cognitive tests looking at executive function, complex tasks, word recall and working memory.

These patients also had higher levels of toxic proteins directly shown to cause Alzheimer’s disease, the most common form of dementia that affects 7million Americans. 

The researchers said the findings of the study, which is still recruiting for larger experiments, are particularly noteworthy because participants were all under 50, suggesting early-onset disease.

While they are unsure what exactly causes the elevated risks, the team suggests it could be due to individuals with ADHD having less brain capacity for age-related degeneration. 

They also pointed toward issues like diabetes and obesity, dementia risk factors, being more prevalent in ADHD populations. 

New research suggests ADHD could lead to signs of dementia in adults (stock image)

Rates of ADHD diagnosis in adults the US are higher than peer nations, CDC figures show

ADHD is a neurodevelopmental disorder that affects focus, impulse control, and energy levels. 

The CDC estimates one in 10 children in the US have been diagnosed with the condition, totaling about 7million, according to the latest data available. 

About 15.5million adults have the disorder.  

The researchers recruited 25 people who were originally part of the Pittsburgh ADHD Longitudinal Study (PALS) at the University of Pittsburgh between 1987 and 1996.

Children were observed during an eight-week summer camp and diagnosed with ADHD. All of them were then followed into adulthood.

The average participant age is 44 and eight in 10 are men. 

Participants were given blood tests to detect amyloid and tau, toxic proteins that accumulate in the brain and form plaques, destroying brain cells and causing dementia. 

The blood tests also measured inflammation and signs of cardiovascular disease, which can damage blood vessels and block blood flow. 

The researchers found participants with ADHD scored lower on tests measuring executive function and processing speed, which are how the brain handles problem solving and how quickly it takes in information.

They also scored worse on working memory tests and recalled fewer words than people without ADHD.

The above map shows dementia risk divided by geographic region

Adderall prescriptions have steadily increased over the last 12 years, data shows

Most surprising to the researchers was higher levels of dementia-causing proteins in blood samples from ADHD patients, suggesting early signs of Alzheimer’s disease. 

Dr Brooke Molina, study author and director of the Youth and Family Research Program at the University of Pittsburgh, said during a conference presentation: ‘We found bigger differences than we expected to see at this age. Remember, the mean age is 44 and it’s a fairly tight age range. These are all individuals in their early to mid 40s. 

‘We are seeing elevate Alzheimer’s disease risk. What’s going to happen with that as they age?’

While it’s unclear exactly why people with ADHD are at a greater risk of dementia, researchers suggest it could be because these individuals have a diminished ‘brain reserve.’ 

This means their brain’s capacity to compensate for age-related changes or neurodegenerative processes is diminished, making them more vulnerable to dementia.

Dr Molina also noted people with ADHD are at a higher risk of vascular conditions like high blood pressure, diabetes and obesity due to stimulant medications and a greater chance of unhealthy lifestyle factors.

The experts are still recruiting for larger scale research, as the small sample size was the study’s main limitation.

Dr Molina said: ‘There is lots more that we can do once we finish collecting the data.’