Impact of ambient air pollution on physical activity among adults: a systematic review and meta-analysis

Aims: This study systematically reviewed literature regarding the impact of ambient air pollution on physical activity among children and adults. Methods: Keyword and reference search was conducted in PubMed and Web of Science to systematically identify articles meeting all of the following criteria - study designs: interventions or experiments, retrospective or prospective cohort studies, cross-sectional studies, and case-control studies; subjects: adults; exposures: specific air pollutants and overall air quality; outcomes: physical activity and sedentary behaviour; article types: peer-reviewed publications; and language: articles written in English. Meta-analysis was performed to estimate the pooled effect size of ambient PM2.5 air pollution on physical inactivity. Results: Seven studies met the inclusion criteria. Among them, six were conducted in the United States, and one was conducted in the United Kingdom. Six adopted a cross-sectional study design, and one used a prospective cohort design. Six had a sample size larger than 10,000. Specific air pollutants assessed included PM2.5, PM10, O-3, and NOx, whereas two studies focused on overall air quality. All studies found air pollution level to be negatively associated with physical activity and positively associated with leisure-time physical inactivity. Study participants, and particularly those with respiratory disease, self-reported a reduction in outdoor activities to mitigate the detrimental impact of air pollution. Meta-analysis revealed a one unit (g/m(3)) increase in ambient PM2.5 concentration to be associated with an increase in the odds of physical inactivity by 1.1% (odds ratio=1.011; 95% confidence interval=1.001, 1.021; p-value < .001) among US adults. Conclusions: Existing literature in general suggested that air pollution discouraged physical activity. Current literature predominantly adopted a cross-sectional design and focused on the United States. Future studies are warranted to implement a longitudinal study design and evaluate the impact of air pollution on physical activity in heavily polluted developing countries.