To Örebro University

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by impairing levels of inattention and/or hyperactivity-impulsivity. Symptoms of ADHD, which typically emerge in childhood, may persist until older age with a substantial adverse impact on health and functionality. Yet there is a notable knowledge gap in research on ADHD in older age and the potential associations of adult ADHD with disorders that are common in older age (i.e., age-related disorders). Thus, this thesis aimed to investigate the prevalence rates of ADHD in older age and whether ADHD in adulthood is associated with an increased risk of age-related disorders. 

Study I, a systematic review and meta-analysis, suggests that a considerable number of older adults report elevated levels of ADHD symptoms, while the prevalence of treated ADHD is less than half of the prevalence of clinically diagnosed ADHD. In Studies II, III, and IV, we used data from Swedish population registers. We found that ADHD is associated with an increased risk of dementia and mild cognitive impairment (Study II), which substantially attenuates after controlling for psychiatric comorbidity. Further, ADHD symptoms in adulthood are associated with an increased risk of subsequent cardiometabolic disorders (Study III). The associations attenuate after controlling for educational attainment, psychiatric comorbidity, and lifestyle factors, and they are confounded by genetic factors. Finally, the prediction of cardiovascular risk in adults initiating pharmacological treatment for ADHD may improve by considering novel risk factors (i.e., psychiatric comorbidity and use of other psychotropic medications) in addition to traditional predictors (Study IV). 

Overall, the findings indicate that a substantial number of older adults have increased levels of ADHD symptoms and that ADHD in adults is associated with an increased risk of age-related disorders. Further longitudinal studies, based on both community samples and epidemiological data, are needed to explore the risk of age-related disorders in ADHD, and the underlying mechanisms, until a more advanced older age.