Theses and Dissertations

Attention-deficit hyperactivity disorder (ADHD) is a developmental disorder categorized by symptoms of inattention, impulsivity, and/or hyperactivity. The onset of ADHD symptoms begin to appear in childhood, tend to be persistent into adulthood, and are associated with adverse physical and mental health outcomes (Caye et al., 2016; Yoshimasu et al., 2018). The current study examined the effects of health-promoting behavior (i.e., diet and physical activity) on ADHD symptoms in middle childhood. The sample consisted of 670 twins (30.1% monozygotic, 36.5% same-sex dizygotic, 32.3% opposite-sex dizygotic) from the ongoing longitudinal study, the Arizona Twin Project. The twin’s (51% female) diet, physical activity, and ADHD symptoms were assessed at age 8 (M = 8.45, SD = 0.69) and ADHD symptoms were assessed again at age 9 (M = 9.70, SD = 0.92). Mixed model regression analyses revealed that aspects of diet (i.e., protein, carbohydrates, and fiber) at age 8 negatively predicted ADHD symptoms at age 9. Similarly, sedentary behavior at age 8 negatively predicted ADHD symptoms at age 9, whereas moderate-to-vigorous activity at age 8 positively predicted ADHD symptoms at age 9. Univariate twin analyses revealed that certain aspects of diet (i.e., sugar, vegetable, and fruit consumption) were influenced by environmental factors whereas other aspects of diet (i.e., protein, carbohydrates, calories, fat, and fiber consumption) were influenced by both genetic and environmental factors. Both children’s sedentary behavior and moderate-to-vigorous activity were influenced primarily by genetic factors, with the remaining variance being attributed to non-shared environmental factors. Additive genetic influences explained the majority of the variance in ADHD symptoms. Future research should examine bidirectional effects of activity and diet on ADHD symptoms across childhood.

ADHD is a neurodevelopmental disorder associated with a high rate of comorbidity with anxiety disorders (25-34%). Children with ADHD experience serious adverse outcomes secondary to impairment in executive function, particularly within the domain of working memory (WM), behavioral inhibition (BI), and sustained attention (SA). While executive function deficits in ADHD are well documented, whether and how comorbid anxiety affects cognitive performance are equivocal. One potential explanation is that most studies examine linear relations, yet evidence suggests that anxiety affects performance in a non-linear (quadratic) manner, consistent with the the Yerkes-Dodson Law. The aim of this study was to investigate whether 1) children with ADHD show deficits in WM, BI, and SA relative to typically developing children, 2) comorbid anxiety displays a linear or nonlinear relationship with WM, BI, and SA performance among children with ADHD and 3) between group differences in cognitive performance vary based on levels of anxiety. Linear and non-linear relations between anxiety and cognitive performance were assessed in a sample of 54 boys diagnosed with ADHD and 50 typically developing boys. Anxiety was assessed across dimensions and raters. Results indicate rater and domain-specific effects of comorbid anxiety on cognitive performance. Non-linear relations between children’s self-rated physiological anxiety and Phonological working memory (PHWM), Visuospatial working memory (VSWM), and the Central Executive (CE) were found. Non-linear relations between parent-rated anxiety and PHWM and the CE were also found. However, no significant linear or non-linear effects of anxiety on BI and SA were found. The results indicate that children with moderate self-rated and parent-rated anxiety performed better on WM measures relative to those with low and high levels of self-rated and parent-rated anxiety. The present study was the first to examine and document non-linear effects of anxiety on cognitive performance among children diagnosed with ADHD. Given the results, clinicians should continue to assess anxiety during diagnostic screening in ADHD samples. Treatments should focus on compensating for CE abilities and mitigating high levels of anxiety as it may further impair WM.