By Mary Fetzer

A large study in Sweden has linked ADHD and dementia across generations. It found that parents and grandparents of individuals with ADHD were at higher risk of dementia than the parents and grandparents of individuals without ADHD.

But the study, published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association in September 2021, was unable to determine any cause-and-effect relationship between ADHD and dementia. It’s unclear why the association might exist; the study and its authors suggest that unknown genetic or environmental factors might contribute to both ADHD and dementia.

The study was conducted at the Karolinska Institutet in Stockholm. Le Zhang, a doctoral student in the Department of Medical Epidemiology and Biostatistics at the Institutet, was the lead researcher.

“ADHD is associated with dementia across generations,” Zhang says. “Our study calls attention to advancing the understanding of ADHD and cognitive decline in older age.”

The findings suggest that there are common genetic or environmental contributions to ADHD and dementia, according to Zhang, who added that further studies are needed to understand the underlying mechanisms.

ADHD is one of the most common mental disorders, according to the American Psychiatric Association, affecting an estimated 8.4 percent of children and 2.5 percent of adults. Recent decades have seen a dramatic increase in both the awareness of ADHD as well as the number of new diagnoses.

Worldwide, more than 55 million people live with dementia, and there are nearly 10 million new cases every year, according to the World Health Organization. Research on the development of dementia in people with ADHD has been limited and has delivered conflicting results.

The Karolinska study looked at more than two million people born in Sweden between 1980 and 2001, about 3 percent of whom were diagnosed with ADHD. National registries were used to link the people in the study with biological relatives — in all, about five million parents, grandparents, aunts and uncles — to investigate whether the relatives developed dementia. The rate of dementia for relatives of individuals with ADHD was compared to the rate of dementia for relatives of individuals without ADHD:

• The risk of dementia was 34 percent higher for parents of individuals with ADHD than for parents of individuals without ADHD. The risk for grandparents of individuals with ADHD was 10 percent higher.
• The risk of Alzheimer’s disease, the most common type of dementia, was 55 percent higher for parents of individuals with ADHD than for parents of individuals without ADHD.
• Parents of individuals with ADHD were more likely to have early-onset dementia than late-onset dementia.

The researchers did note, however, that even though parents of kids with ADHD had a significantly increased risk of dementia, their absolute risk remained low. Overall, only 0.17% of the parents identified in the study were diagnosed with dementia during the follow-up period.

The study found no cause-and-effect relationship between ADHD and family members’ dementia. So reasons for the association remain unclear.

“This study is interesting and definitely warrants further exploration,” says behavior analyst Ryan Bolling, CEO of Bolling Behavioral Consulting in Atlanta. “That said, I would not say that I agree with the findings wholeheartedly. I think more studies are needed to really understand the implications of this study.”

The largest genetic studies on ADHD and dementia to date “have failed to detect any genetic variant in common,” Zhang says, but there have been studies suggesting that certain genes may be implicated in both ADHD and dementia.

“One could imagine that there are undiscovered genetic variants that contribute to both traits, or family-wide environmental risk factors, such as socioeconomic status, that may have an impact on the association,” says Zheng Chang, a researcher at Karolinska Institutet and a co-author of the study. “Another possible explanation is that ADHD increases the risk of physical health conditions, which in turn leads to increased risk of dementia.”

The researchers note that a family’s overall risk of developing ADHD or dementia, or both, can be influenced by outside factors as well. Financial distress, substance use and obesity were some of the potential influences considered by the researchers.

As an example, Zhang notes that ADHD in children and adults has been associated with excess weight, and obesity in middle age has been linked with an increased risk of dementia later in life.

The bottom line, however, is that correlation does not indicate causation. More research is needed to determine precisely why and how ADHD and dementia are related.

“This is an association study; it shows that two things are somehow connected,” Heather Snyder, vice president of medical and scientific relations at the Alzheimer’s Association, tells United Press International. “Because of how the study was conducted, it does not — and cannot — prove causation. But it is interesting all the same.”

New York City psychiatrist Jeff Ditzell agrees that more research is needed.

“Linking ADHD to dementia is a controversial topic with many questions surrounding whether they are related,” Ditzell says. Determining what, if anything, connects them may guide future treatment of both disorders, he says.

Sources:

Science Daily: Link between ADHD and dementia across generations

American Psychiatric Association: What is ADHD?

World Health Organization: Dementia

United Press International: Multigenerational study finds links between ADHD, dementia risk