Association of decreases in PM2.5 levels due to the implementation of environmental protection policies with the incidence of obesity in adolescents: A prospective cohort study

Aims: To explore the association between decreased levels of particulate matter (≤2.5 µm; PM) due to the implementation of environmental protection policies and the incidence of obesity in adolescents in Chongqing, China through a prospective cohort study. Methods: A total of 2105 children (52.02% male; aged 7.33 ± 0.60 years at baseline) were enrolled from the Chongqing Children's Health Cohort. A mixed linear regression model was used to analyse the relationships of PM levels with obesity indicators after adjusting for covariates. Additionally, a Poisson regression model was used to determine the relationship between PM exposure and the incidence of overweight/obesity. Results: The average PM exposure levels from participant conception to 2014, from 2015 to 2017, and from 2018 to 2019 were 66.64 ± 5.33 μg/m, 55.49 ± 3.78 μg/m, and 42.50 ± 1.87 μg/m, respectively; these levels significantly decreased over time (P < 0.001). Throughout the entire follow-up period, the incidence of overweight/obesity after a ≥ 25 μg/m decrease in the PM level was 4.57% among females; this incidence was the lowest among females who experienced remarkable decreases in PM exposure. A 1-µg/m decrease in the PM level significantly decreased the body mass index (BMI), BMI z score (BMI), and weight of adolescents (all P < 0.001). Compared with a < 20-μg/m decrease in the PM level, a ≥ 25-μg/m decrease protected against increased BMI (net difference= −0.93; 95% confidence interval [CI]: (−1.23,−0.63) kg/m), BMI (−0.28 (−0.39, −0.17)), weight (−1.59 (−2.44, −0.74) kg), and incidence of overweight/obesity (0.48 (0.37, 0.62), P < 0.001). Moreover, compared with a < 20-μg/m decrease in the PM level, a ≥ 25-μg/m decrease resulted in significant absolute differences in BMI (−1.26 (−1.56, −0.96) kg/m), BMI (−0.53 (−0.65, −0.40)) and weight (−3.01 (−3.8, −2.19) kg) (all P < 0.001). Conclusions: This study showed the etiological relevance of declining PM concentrations for the incidence of obesity in children and adolescents, suggesting that controlling ambient air pollutants may prevent the development of obesity in this age group. Continuous implementation of environmental protection policies in China has led to substantial health benefits.