The Association between Levels of Physical Activity and Asthma Incidence: A Systematic Review and Meta-Analysis

Abstract

Background: The prevalence of global asthma is high especially in high-income countries, leading to increased efforts to find easily modified risk factors that can lower the risk of developing this disease. Physical activity has been suggested to be one of those factors but the prevalence of inactivity has also increased recently. A number of cohort studies have investigated the influence of physical activity on asthma incidence with inconsistent results. Objective: Perform a systematic review and meta-analysis to quantify the effects of high levels of physical activity on the risk of developing asthma. Data sources: Pubmed, Scopus and checking the reference lists of all included studies. Study selection: English language longitudinal (cohort) studies looking at leisure time physical activity as the exposure and asthma incidence as the outcome. Excluding studies using other designs or looking at lab measured physical fitness or specific disease populations. Results: The search retrieved 1103 articles, of which 61 were read in full text and eight of those articles were included in this review. The crude and adjusted meta-analyses showed no association overall between physical activity and asthma incidence, while a crude subgroup analysis of studies with only adult participants showed that high physical activity lowers the risk of developing asthma (OR=0.86, 95% CI: 0.77-0.96) with low heterogeneity (I2=3.6%). Conclusion: There was a crude association showing high physical activity lowers the risk of developing asthma for adults but it disappeared in the adjusted analysis. The overall result of no association between physical activity and asthma incidence might be inaccurate due to studies adjusting for different confounders or not adjusting for all the potential confounders of this association. Additionally, studies have mostly used non population-based participants among other reasons. Further representative longitudinal studies of this association are needed especially for children.