Attention deficit hyperactivity disorder (ADHD) has been linked to Alzheimer’s disease and other dementias in what the researchers say is the first study of its kind.

Investigators looked at the extent to which ADHD is tied to Alzheimer’s and any dementia across generations in a Swedish nationwide cohort born between 1980 and 2001. They used the same national registry to link study participants to biological relatives including parents, grandparents, aunts and uncles.

Parents of children diagnosed with ADHD were more likely to receive a diagnosis of Alzheimer’s than their peers whose children did not have ADHD, the researchers found. What’s more, these parents were more at risk of developing early-onset Alzheimer’s than late-onset disease. Similar results were found for any other dementia.

An association also was seen between Alzheimer’s, dementia and ADHD for the grandparents of the main study cohort, but it was smaller than that of the parents, reported Zheng Chang, Ph.D., of the Karolinska Institute in Sweden, and colleagues. Aunts and uncles had an elevated, but not statistically higher risk of Alzheimer’s disease and dementia.

Genetic and environmental risk factors tied to ADHD may explain some of the association between ADHD, a neurodevelopmental disease often diagnosed in childhood, and dementia, a neurodegenerative condition that usually develops in older adulthood, Chang and colleagues proposed.

“[T]hese risk factors may represent factors unique to ADHD (independent of Alzheimer’s disease), which in turn increase the risk of ADHD in both the index persons and their relatives, and further increase the risk of Alzheimer’s disease via adverse health outcomes triggered by ADHD,” they wrote. 

One example of such factors is obesity, which is linked to ADHD in childhood and dementia in mid-life, Chang explained. Environmental risk factors, meanwhile, might include ADHD-associated behaviors within the family, the investigators added.

The findings highlight the need for a better understanding of ADHD and cognitive decline in older age, the authors said. If the results hold up under further scrutiny, they warrant further investigation of early-life psychiatric prevention on the development of neurodegenerative diseases in older age, they concluded.

The study was published in the journal Alzheimer’s & Dementia.