Gymnastik- och idrottshögskolan, GIH

Background Attention-deficit/hyperactivity disorder (ADHD) symptoms are associated with adverse health outcomes; this may be partially due to unhealthy lifestyle factors such as low physical activity (PA) and high sedentary behavior (SED). However, this association remains unclear. ADHD and PA have a medium-to-high heritability; therefore, genetically informed studies are warranted. This study aimed to increase the understanding of the association between ADHD symptoms and time spent in PA and SED in children. Additionally, we aimed to determine whether sex, symptom type, and genetics influence this association. This could guide the design of health promotion and preventive interventions.Methods This cross-sectional twin study included 9-year-old children from the Swedish Twin Registry born from 2011 to 2015 who had complete data on ADHD symptoms and accelerometry. ADHD symptoms were assessed through a parental-report questionnaire. Inattention and hyperactivity/impulsivity symptoms were analyzed together and separately. Triaxial accelerometry measured the average time (minutes) spent in SED, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA). Linear generalized estimating equations regression models were used to assess the association in the full cohort and stratified by sex. Within-twin pair analyses were performed separately for dizygotic and monozygotic twins. Regression coefficients and 95% confidence intervals (CI) were calculated.Results 1966 children (52.8% girls) were included. In the full cohort, ADHD symptoms were significantly associated with less time in SED (beta = -0.32; 95% CI -0.59, -0.06) and more time in MVPA (beta = 0.30; 95% CI 0.12, 0.47). These associations were primarily driven by hyperactivity/impulsivity symptoms and were significant only in girls. The associations remained in dizygotic twins but became non-significant among monozygotic twins.Conclusion Our findings suggest that in girls, higher hyperactivity/impulsivity symptoms are associated with higher PA levels. Associations were largely explained by shared familial factors, including genetics. Longitudinal studies are needed to corroborate these results.

Physical activity (PA) plays a key role in children's health, yet it remains unclear why girls are often less active and more sedentary than boys. This study examined genetic and environmental (shared and non-shared) influences on device-measured PA and sedentary time (SED) across girls and boys. This cross-sectional study contained data on zygosity, sex, PA, and SED for 2046 9-year-old twins in Sweden. The accelerometer-measured PA was expressed as the proportion of time in SED, light (LPA), moderate (MPA) or vigorous PA (VPA). Structural equation modelling within a twin framework estimated the heritability of PA and SED, decomposing variance into additive genetic (A), shared environment (C), and non-shared environment (E). Quantitative sex differences were examined by allowing the variance components (A, C, E) to differ across sexes. In the total cohort, genetic contribution was highest in VPA (Atotal: 0.64) but lower in SED, LPA and MPA (Atotal: 0.50-0.55). Boys and girls had differing patterns of genetic contributions, with the largest contributions among girls found for LPA (Agirl: 0.44; Aboy: 0.37) while the genetic contribution in VPA was larger in boys (Agirl: 0.15; Aboy: 0.57), and the difference was statistically significant for VPA (p = 0.001). While the non-shared environment was similar in all models, the shared environment showed the opposite pattern to the genetic contributions. This twin study shows that genetic influences on PA and SED differ by sex, highlighting the importance of considering how biological mechanisms that drive activity patterns might differ across sex, especially in vigorous physical activity.

PURPOSE: The transition phase between childhood and adolescence is critical, given the observation of increased mental health issues during this period, coupled with the absence of efficient intervention tools. This study aims to examine a possible effect of physical activity on mental health symptoms in adolescents during this transitional age.

METHODS: We used data from a large-scale population-based Swedish twin sample of 14,083 individuals to investigate cross-sectional and longitudinal associations between physical activity and mental health problems during childhood and adolescence. We examine different aspects of mental health symptoms, including internalizing and externalizing symptoms. We applied generalized estimating equations to investigate the associations and explored potential familial confounding using within-twin pair analysis.

RESULTS: We found high physical activity intensity and frequency to be associated with better mental health throughout childhood and adolescence, cross-sectionally and longitudinally. Compared to those who reported low, those reporting high physical activity intensity and frequency in both childhood and/or adolescence had significantly lower symptoms of mental health at age 15. This association was statistically significant for both internalizing and externalizing symptoms. The within-twin pair analysis showed that familial confounding factors can largely explain the association with the externalizing scale, but not the internalizing scale.

DISCUSSION: Physical activity in childhood and adolescence may play an essential role in reducing the risk of developing mental health problems, especially internalizing symptoms. Implementing acceptable, low-risk, and cost-effective interventions to promote physical activity could effectively safeguard young individuals from these symptoms.