Background: The association of asthma and obesity in youth is well studied. However, much of this research has been observational and the temporal relationship between the two factors remains the subject of debate. Moreover, there are mixed findings regarding the role of physical activity in the association between asthma and obesity in youth. Methods: A systematic review of existing literature of the relationship between asthma and obesity in youth, while examining the role of physical activity as a mediator, was conducted using PubMed and Medline databases. Studies conducted on children and adolescents aged 0 to 18 years, published in English during the period of 2000 to 2014 were included. A comprehensive search yielded 143 studies in PubMed and 133 studies in Medline databases. Of these, 76 studies met the review’s eligibility criteria. The Strengthening the Reporting of Observational Studies in Epidemiology guidelines were consulted to evaluate quality of selected citations. Results: The association between asthma and obesity in youth is well explored. However, there are varying hypotheses and conclusions regarding this relationship, of which temporality remains to be elucidated. Existing evidence was identified to support the mediation of this association by physical activity. Negative self- or parental- perception of exercise ability due to asthma symptoms secondary to physical exertion was identified as a determinant of physical activity in asthmatic youth. Also, control of asthma symptoms was found to directly impact daily physical activity levels. Greater odds of increased weight were observed among asthmatic children compared to non-asthmatic peers. However, annual weight gain was found to be similar among asthmatic children with well controlled symptoms to that of their healthy peers. Lastly, the review found that adverse respiratory symptoms secondary to exercise are experienced by 90% of asthmatic youth, resulting in activity limitation. According to this finding, it is reasonable that the incidence of obesity frequently observed to be greater in asthmatic youth than healthy peers is mediated by decreased expenditure of energy in asthmatic children due to reduced physical activity. Conclusions: It is likely that physical activity mediates the relation between asthma and obesity, though further research is required to determine the temporal relation and degree of this association.
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