Physical activity and asthma in youth: cause or consequence?

© 2020 Raisa CassimAsthma is the most common chronic disease in children, and often persists into and adulthood. Further, despite its known health benefits, it is estimated that more than 80% of the world’s adolescents are insufficiently physically active. Since both asthma and physical inactivity are significant problems in child and adolescent populations, it is essential to focus research on these populations. The relationship between asthma and physical activity is complex and controversial, and the temporality of these associations remains unclear. My doctoral work attempted to tease out these relationships. This work was divided into sections with distinct research questions, which together aimed to advance our current understanding of the relationship between asthma and physical activity in children and adolescents. Hence, this thesis contains two systematic reviews which were performed in order to understand the existing literature on the nature of the relationship between physical activity and asthma in children. These reviews are followed by three data analyses which employed a variety of statistical techniques to analyse data from questionnaires, accelerometry and clinical assessments collected by two well-established cohorts of Australian children: The Longitudinal Study of Australian Children (LSAC) and the HealthNuts study. The first of the two systematic reviews found no evidence that children and adolescents with and without asthma participated in different amounts of objectively measured physical activity. The second review, which aimed to investigate the effect of physical activity on subsequent asthma outcomes, found insufficient evidence to determine the effect of physical activity on subsequent asthma and lung function outcomes. Hence, in the first data analysis, I aimed to elucidate the direction of the association by investigating the possibility of bidirectionality. However, there was no evidence of longitudinal associations in either direction. Next, I compared the amount of time spent in moderate to vigorous physical activity (MVPA) between children and adolescents with and without asthma at 5 different ages and again found no evidence that youth with and without asthma engaged in differential amounts of time in physical activity. Finally, I investigated the effect of early wheeze and asthma on objectively measured physical activity in early childhood and again found no evidence that children who experience early life asthma and wheeze were less active at a later age. Thus, my thesis presents sustained and compelling evidence of a lack of association between asthma and physical activity in youth – in either direction. A number of implications can be drawn from these findings. First, physical activity campaigns targeted at children need not focus specifically on children with asthma. Second, the effect of physical activity on future asthma outcomes remains unclear. However, even without evidence that physical activity is beneficial for future asthma outcomes, physical activity should be encouraged from a young age for its many other health benefits