Is adult ADHD associated with an increased risk of dementia?

By Priyanjana Pramanik, MSc.Reviewed by Lily Ramsey, LLMOct 19 2023

In a recent study published in JAMA Network Open, researchers explored the associations between adult attention-deficit/hyperactivity disorder (ADHD) and the risk of cognitive decline. Their results indicate that individuals with ADHD are more likely to be diagnosed with dementia.

Study: Adult Attention-Deficit/Hyperactivity Disorder and the Risk of Dementia. Image Credit: Roman Bodnarchuk/Shutterstock.com

Background

Dementia is a cognitive condition that affects the daily functioning of millions worldwide, causing disability and death. As the global population ages, the dementia burden is expected to increase. However, relatively little research has investigated the risk factors influencing this condition or how it can be effectively prevented.

Some of the factors thought to be associated with increased dementia risk are low education, physical inactivity, smoking, diabetes, hypertension, and depression. Epidemiological risk studies and clinical observations also point to the possible role of adult ADHD. For instance, memory loss is a symptom of both adult ADHD and dementia. Medical professionals see adult ADHD as a condition distinct from ADHD in children, but it has not been well studied.

Previous studies exploring the relationship between adult ADHD and dementia were inconclusive. Some found significant associations, while others did not. They were unable to exclude the possibility of biases, confounding factors, and reverse causation.

These studies also identified another avenue for investigation – whether the association, if any, was stronger for men compared to women. More research in this field will benefit patients and their caregivers, as well as clinicians and policymakers.

About the study

The present study used a prospective birth cohort design to explore the link between adult ADHD and dementia. Data was obtained from the health records of an Israeli nonprofit legally prohibited from refusing treatment based on demographics or pre-existing conditions. This allowed the researchers to reduce the effect of selection bias in their sample.

The study participants were all Israeli citizens born between 1933 and 1952. At the beginning of the study in 2002, they did not have ADHD or dementia diagnosis, nor were they under medication for these two conditions. From 2003 to 2020, the cohort was followed up until they were diagnosed with dementia, left the provider, or passed away.

Dementia diagnoses were based on the International Classification of Diseases (ICD) and provided by trained healthcare providers such as psychiatrists, neurologists, or geriatricians. Similarly, ADHD was diagnosed using the same international guidelines and assessed by board-certified medical professionals using standardized neuropsychological assessments.

The research team considered covariates that could confound the relationship between ADHD and dementia, such as demographics, comorbidities, and medication use. Demographics included age, sex, and neighborhood socioeconomic status. Smoking status was also included. Comorbidities included obesity, depression, heart and cerebrovascular conditions, Parkinson’s disease, migraines, and traumatic brain injuries. Medications included nootropics and psychostimulants.

For the analysis, researchers calculated hazard models for the risk of dementia, with ADHD as a time-varying as well as static covariate. They adjusted these base models using other confounding factors and also ran 14 additional analyses to validate their initial findings, considering various subgroups that could have differential risks of dementia. Sensitivity analysis was used to assess the possibility of reverse causation.

Findings

The cohort included 109,218 participants, of whom 51.7% were female and 48.3% were male. At the beginning of the follow-up period, they were 57.7 years old on average. Participants with ADHD were, on average, two years younger than those without an ADHD diagnosis.

A total of 730 individuals, or 0.7% of the sample, were diagnosed with adult ADHD throughout the study, and 7726 people, or 7.1%, received a dementia diagnosis. Preliminary analysis showed that 42.9% of those with an adult ADHD diagnosis were also diagnosed with dementia at age 85, compared to only 15.2% of those without an ADHD diagnosis.

The hazard ratio analysis provided similarly striking results – those with adult ADHD had a hazard ratio of 3.62, and they were more than 2.5 times likelier to be diagnosed with dementia. Once the model was adjusted with other covariates, the hazard ratio declined to 2.77 but was still significant.

There were no conclusive differences in these trends based on sex, smoking status, age, or medication use. A sensitivity analysis based on stratified follow-up durations found some evidence of reverse causation.

Conclusions

The present study explored the associations between adult ADHD and incident dementia while making efforts to navigate selection biases and various confounding factors. Even the most conservative estimate from adjusted models indicates that an adult ADHD diagnosis increases the risk of developing dementia by more than 1.5 times.

The researchers identified several limitations that provide avenues for further investigations. They could not access data on whether their participants had been diagnosed with ADHD as children. They also relied on clinical and not research diagnoses, which could lead to an underestimate in the incidence of ADHD. Similarly, they raised concerns that dementia could have been underestimated in their population.

Further studies, they hope, will also delve deeper into the role of education and psychostimulant medication.The results of this study cannot be interpreted through a causal lens, as they are based on observational data.