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.
“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,” said Zheng Chang, researcher at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet, and the study’s last author.