Attention Deficit/Hyperactivity Disorder and Risk of Dementia: A Systematic Review and Meta-Analysis

Introduction: The significant impact of attention deficit/hyperactivity disorder (ADHD) on health in adult life has been widely recognized. Among the comorbidities of this disorder in later life, dementia is one of the most relevant ones. We performed a systematic review and meta-analysis to explore the impact of previous ADHD diagnosis on dementia risk. Materials and methods: We systematically searched Pubmed, Embase and Scopus for the relevant literature. Cohort and case–control studies were included in our review. Retrieved records were selected by title and abstract and then by full text reading. For quality appraisal, the Newcastle–Ottawa scale was used. A meta-analysis of hazard ratios (HRs) was performed for each type of dementia. Results: Four cohort studies and one case–control study were included, for a total of 3,703,877 and 400 participants, respectively. For all-cause dementia, the pooled HR was 2.52 (95%CI 1.51–4.22, p < 0.001), pointing out a significantly higher hazard in subjects with ADHD. For Alzheimer’s disease, vascular dementia and Lewy body dementia, no meta-analysis was performed due to the low number of available studies. Discussion and conclusions: Our results support a significant association between ADHD and risk of dementia. The results regarding specific types of dementia are more challenging to interpret and could have been influenced by sample size issues. These findings show that ADHD deserves attention in future research on cognitive disorders of the elderly; in particular, more studies are needed to reveal if a true causal relationship links ADHD and dementia.