Study Shows Adults with ADHD Have Three Times Higher Risk of Developing Dementia

The risk of developing dementia is almost three-fold among adults diagnosed with attention-deficit/hyperactivity disorder (ADHD), compared to those without this condition. This conclusion is from a recent study.

The research findings were publicised in the JAMA Network Open last week. It considered over 109,000 older Israeli adults to ascertain if those with ADHD were at a higher risk for dementia, including Alzheimer’s disease.

The team of researchers mentioned that even though dementia is prevalent among the elderly, it's exact etiology is not very clear. However, some earlier studies have indicated a connection between ADHD and neurodegenerative diseases.

Michal Schnaider Beeri, PhD, Director of the Herbert and Jacqueline Krieger Klein Alzheimer’s Research Center at Rutgers University and a co-author of this study, shared their curiosity to understand how brain conditions like ADHD could lead to dementia in older people.

She further stated that understanding such connections could aid in devising prevention strategies for high-risk populations and provide insight into the novel mechanisms connecting both conditions.

Dementia, not a specific disease but a symptom group typified by dysfunction in everyday life owing to cognitive impairment, is among the leading causes of disability and death. It is anticipated that 6.7 million U.S. adults aged 65 or older will have this condition in 2023, and the number might surge to 13.8 million by 2060.

Although classified as a neuro-developmental disorder, ADHD symptoms could comprise not paying close attention to details, intruding on others and difficulty participating in quiet leisure activities.

Beeri indicated that ADHD-affected individuals, especially those not receiving appropriate treatments or with poorly managed cases, could have impulse control problems, leading to adverse lifestyle choices.

These could include unhealthy dietary habits, lack of exercise, obesity and hypertension, cumulatively increasing the dementia risk. Moreover, she suggested that ADHD's neurobiology could lead to exacerbated brain and cognitive reserve risks, thereby escalating the susceptibility to old-age dementia.

To comprehend the association between ADHD and dementia, the researchers utilized data from a national cohort study involving over 109,000 individuals born between 1933 and 1952 and observed from 2003 to 2020.

None of the participants had been diagnosed with ADHD or dementia when the observation began. Nearly half of them were male and half female.

The researchers discovered that even accounting for other dementia risk factors, ADHD-diagnosed adults had a 2.77-fold increased dementia risk.

Throughout the follow-up, 730 participants (0.7%) were diagnosed with adult ADHD, and over 7,700 (7%) received a dementia diagnosis. Among the adults with ADHD, 13% developed dementia, compared to 7% without this disorder.

The researchers are yet to determine the exact reasons behind the connection between adult ADHD and dementia. Sven Sandin, PhD, an associate professor of psychiatry at the Icahn School of Medicine at Mount Sinai and a co-author of this study, expressed uncertainty over the link between the genetic causes of ADHD and dementia.

Several other studies have reported similar conclusions. One 2022 study showed that individuals diagnosed with ADHD were at a higher risk for dementia and mild cognitive impairment. However, when considering psychiatric disorders like depression, anxiety, substance abuse disorder, and bipolar disorder, the risk diminished.

A 2023 study also indicated ADHD as a less frequent, but plausible contributor to cognitive impairment disorders like dementia.

Links between childhood ADHD and adult ADHD are strong, but the two conditions often vary in their experiential aspects, depending on ADHD's diagnosis time. Around 5% of children with ADHD meet the adult ADHD criteria, constituting 3% of all adult ADHD cases. However, research has shown that child and adult ADHD are dissimilar in their social, psychological, and genetic facets, and detailed information on adult ADHD is limited.

Beeri stated that while ADHD is a chronic condition, starting in childhood and continuing to adulthood, it is uncertain whether the risk varies with the time of diagnosis. However, she did note that, certain features suggest ADHD in childhood and adulthood could be two distinct conditions.

However, researchers noted that for this particular study, they lacked information on child onset ADHD and their exact symptomatology.

“Furthermore, our study established an association between adult ADHD and dementia,” said Sandin. “However, future studies are needed to closer examine the causal path, for example, the associations may be due to unknown confounding factors—genetic or environmental.”

Beeri emphasized that their findings don’t prove that ADHD causes dementia, just that there appears to be a link.

“Based on our findings, we can only state that there is a relationship between ADHD and dementia,” she said. “Little evidence of reverse causation suggests that, if biologically connected, ADHD might lead to dementia rather than the other way around.”

She added that it’s important to note that when accounting for medication, the link between ADHD and dementia weakens.

This could imply that medicated individuals might not have an increased dementia risk. Alternatively, it might indicate that medicated individuals represent true ADHD patients with severe symptoms.

”Further research is necessary to explore potential common biological mechanisms between ADHD and dementia,” said Beeri. “Additionally, clinical trials are needed to investigate whether psychostimulants can reduce dementia risk in older adults with a history of ADHD.”

The study also noted that adult ADHD may be associated with an increased risk of dementia based on common health outcomes that have modifiable risk factors like depression, midlife hypertension, and smoking.

“In addition to adult ADHD, diabetes, high blood pressure, and lack of physical exercise all increase dementia risk,” said Sandin. “In the context of these many risk factors, one should try to preserve both good general health and good cognitive health.”