Somatic and occupational outcomes in adult ADHD : epidemiology studies based on real-world data

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders, characterized by inattention or hyperactivity–impulsivity, or both. ADHD is a multifactorial disorder influenced by the complex interplay between genetic and environmental risk factors, but a detailed understanding of the causal status of these factors is lacking. ADHD is associated with many psychiatric disorders, but somatic comorbidity in ADHD has received less attention in the research literature. Pharmacological treatment is effective in reducing the core symptoms of ADHD, but the effects on occupational outcomes remain unclear. The overarching aim of this thesis is to extend previous knowledge on the early risk factors of ADHD, and to increase the awareness and the understanding on somatic and occupational outcomes of ADHD in adults. In Study I, we combined a systematic review and mate-analysis with a population based cohort of 971,501 individuals born between 1992 and 2004 in Sweden. The meta-analysis revealed a positive association between maternal pre-pregnancy overweight/obesity and risk of ADHD in offspring. However, these associations gradually attenuated toward the null when adjusted for measured confounders,unmeasured factors shared by cousins and unmeasured factors shared by siblings. In Study II, by using a Swedish population-based twin study with 17,999 individuals aged 20–47 years, we found both inattention and hyperactivity/impulsivity was associated with higher consumption of high-sugar food and unhealthy dietary habits, although these associations were generally weak. Further, the observed associations was explained by both genetic and non-shared environmental factors.In Study III, we explored the prospective associations between ADHD and a broad range of cardiovascular diseases in 5,389,519 adults from Sweden, and found that ADHD may be a novel and independent risk factor for cardiovascular diseases. In Study IV, based on the longitudinal cohort of 12,875 middle-aged adults with ADHD, we found the use of ADHD medications during the previous two years was associated with a 10% reduction in the risk of long-term unemployment in the following year. Taken together, findings from the thesis highlight the need of future studies with various study designs, to fully understand the aetiology and long-term health outcomes of ADHD across the lifespan