Interaction Between Long-Term Exposure to Fine Particulate Matter and Physical Activity, and Obesity: Analysis of a Chinese Nationwide Cross-Sectional Study

Abstract

Background: Obesity has become a global epidemic and concern and physical activity (PA) is suggested to be a protective factor. However, PA during air pollution may increase the inhaled load caused by augmented ventilation. We aimed to assess whether the air pollution would attenuate the benefits of PA on obesity. Methods: In this study, 91,121 Chinese adults above 18 years old were recruited from 31 provinces in mainland China by a multi-stage stratified-clustering random sampling method. The exposure to PM2·5 was estimated at the township level using a validated machine learning method with a spatial resolution of 0·1° × 0·1°. The PA was measured with a standard questionnaire and its level was defined as metabolic equivalent (MET). The overall PA in MET- minutes/week was calculated by summing it across all activities. Body weight, height, and waist circumference (WC) were measured by trained technicians after overnight fasting. Obesity-related traits included continuous outcomes (body mass index (BMI), WC, and waist-to height ratio (WHtR)) and binomial outcomes (general obesity, abdominal obesity, and WHtR obesity, which were defined based on BMI, WC, and WHtR, respectively). Generalize linear regression models were used to estimate the independent association of PA and combined association of PM2·5 and PA on obesity-related traits, controlling for confounders. Interaction plots were used to exhibited the estimated association of PA on obesity as a function of concentration of PM2·5. Findings: The overall prevalence of inactive Chinese adults was 39.8% and the one-year average PM2·5 concentration was 58·5 µg/m3 (SD: 17·9µg/m3). Each 10- MET hour/week increase in PA was associated with 0·012 [95% confidence interval (CI): 0·015, 0·010] kg/m2, 0·054 (95% CI: 0·061, 0·046) cm, and 0·0003 (95% CI: 0·0004, 0·0002) decrease in BMI, WC, and WHtR, respectively. We observed the protective associations of PA on obesity-related traits were decreased with the increasing of the PM2·5 concentration. Interpretation: Higher PA was strongly associated with lower obesity risk in people exposed at various level of PM2·5. Our results suggested that PA is a suitable strategy to prevent obesity for population lived in relatively polluted regions. Funding Information: This study was supported by grants from the National Natural Science Foundation of China (41977374). Declaration of Interests: The authors declare no conflict of actual or potential competing financial interests. Ethics Approval Statement: The study protocol was approved by the ethical review committee of the Chinese Center for Disease Control and Prevention (CDC) (Reference No.: 201010). All study participants provided written informed consent.