“Attention-deficit/hyperactivity disorder and Alzheimer’s disease and any dementia: a multi-generation cohort study in Sweden,” L. Zhang, E. Du Rietz, R. Kuja-Halkola, M. Dobrosavljevic, K. Johnell, N. L. Pedersen, H. Larsson, and Z. Chang, Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, online Sept. 9, 2021, doi: 10.1002/alz.12462
By Taina Lehtonen
The impact of ADHD can be observed throughout the lifespan, and it might be linked to neurodegenerative conditions, such as Alzheimer’s disease or any dementia.
For a long time, ADHD was considered a childhood disease that people grow out of after entering adulthood. Now we know that ADHD in many cases persists into adulthood. The symptoms of ADHD in adults may be more diverse and subtle when compared to children and adolescents, and it can be difficult to diagnose in older adults.
This large study from Karolinska Institutet in Sweden has found a link between ADHD and dementia across generations. It shows that parents and grandparents of individuals with ADHD were at higher risk of dementia than those with children and grandchildren without ADHD.
Since there is still relatively little knowledge of ADHD in old age, there has only been a limited number of small studies on the development of dementia in people with ADHD, often with conflicting results.
In this study, the researchers wanted to examine to what extent older generations of individuals with ADHD were diagnosed with dementia. The study looked at more than two million people born in Sweden between 1980 and 2001, of whom around 3.2 percent were diagnosed with ADHD. Using national registries, the researchers linked these persons to over five million biological relatives, including parents, grandparents and uncles and aunts, and investigated to what extent these relatives developed dementia.
The researchers found that parents of individuals with ADHD had 34 percent higher risk of dementia than parents of individuals without ADHD. The risk of Alzheimer’s disease, the most common type of dementia, was 55 percent higher in parents of individuals with ADHD.
Individuals with ADHD were more likely to have parents with early-onset dementia than late-onset. The researchers note that the absolute risk of dementia was low for the parent cohort; only 0.17 percent of the parents were diagnosed with dementia during the follow-up period.
The association was lower for second-degree relatives of individuals with ADHD, i.e. grandparents and uncles and aunts. For example, grandparents of individuals with ADHD had 10 percent increased risk of dementia compared to grandparents of individuals without ADHD. While the study is unable to determine a cause-and-effect relationship, the researchers present several potential explanations that can be explored in future research.
Research on underlying risk factors contributing to both ADHD and AD are warranted. This study calls attention to advancing the understanding of ADHD and cognitive decline in older age, and, if verified, warrants investigation of treatment of ADHD to prevent or delay the development of neurodegenerative diseases in individuals with ADHD and their family members.
Due to the nature of longitudinal studies, it may take several decades to arrive at a definitive answer to link between ADHD and dementia, and whether ADHD treatment in childhood and adulthood can influence risk of Alzheimer’s disease or any dementia in the future. This study contributes with new knowledge on the subject link between ADHD and dementia across generations.
We examined the extent to which attention-deficit/hyperactivity disorder (ADHD), a neurodevelopmental disorder, is linked with Alzheimer’s disease (AD) and any dementia, neurodegenerative diseases, across generations.
A nationwide cohort born between 1980 and 2001 (index persons) were linked to their biological relatives (parents, grandparents, uncles/aunts) using Swedish national registers. We used Cox models to examine the cross-generation associations.
Among relatives of 2,132,929 index persons, 3042 parents, 171,732 grandparents, and 1369 uncles/aunts had a diagnosis of AD. Parents of individuals with ADHD had an increased risk of AD (hazard ratio 1.55, 95% confidence interval 1.26–1.89). The associations attenuated but remained elevated in grandparents and uncles/aunts. The association for early-onset AD was stronger than late-onset AD. Similar results were observed for any dementia.
ADHD is associated with AD and any dementia across generations. The associations attenuated with decreasing genetic relatedness, suggesting shared familial risk between ADHD and AD.