Objectively measured the impact of air pollution on physical activity and sedentary behavior in freshmen student in Beijing, China

Background: Air pollution has become a major environmental health risk factor, notably in China. Air pollution potentially has the impact of human populations’ health behavior. Gaps in scientific literature remain regarding more accurately estimates the relationship between air pollution and sedentary behavior in China. The purpose of this study is to examine the effect of hourly air pollution on hourly physical activity (PA) and sedentary behavior (SB) among college students living in Beijing, China. The secondary aim was to examine such associations varied at specific time. Methods : Participants were recruited included 340 freshmen students from Tsinghua University. Accelerometers provided PA measures, including moderate-to-vigorous physical activity (MVPA), walking steps, energy expenditure, and sedentary time for 7 consecutive days. Corresponding air pollution data collected by Beijing Municipal Ecological Environment Bureau in the closed site in Tsinghua University were measured to include average hourly air quality index (AQI) and PM 2.5 (µg/m³). Associations were estimated using linear individual fixed-effect regressions. Results: A one level increase in hourly air quality index (AQI) was associated with an reduction in one-hour physical activity by 0.083 (95% confidence interval [CI] =-0.137, -0.029) minutes of MVPA, 8.822 (95% CI = -15.028, -2.617) walking steps, 0.653 (95% CI =-1.033, -0.273) kcals of energy expenditure. A 10µg/m³ increase in air pollution concentration in hourly PM 2.5 was associated with a reduction in one-hour physical activity by 0.021 (95% confidence interval [CI] =-0.033, -0.010) minutes of MVPA, 2.232 (95% CI = -3.548, -0.916) walking steps, 0.170 (95% CI =-0.250, -0.089) kcals of energy expenditure and an increase in one-hour sedentary behavior 0.045 (0.005, 0.0845). At specific time, stronger negative associations of AQI and PM 2.5 air pollution with PA at 8 am, 4 pm, 5 pm and 7 pm. Similarly, stronger positive associations of one hour AQI and PM 2.5 air pollution with SB at 8 am, 9 am, 11 am, and 7 pm. Conclusions: Air pollution decrease physical activity and increases sedentary behavior among freshman students living in Beijing, China. The impact of air pollution on physical activity and sedentary behavior at a specific time was different.