Long-term effect of intermediate particulate matter (PM) on incident asthma among middle-aged and elderly adults: A national population-based longitudinal study.

Background: There is insufficient evidence about the long-term effects of intermediate particulate matter (PM) on asthma development in adults aged 45 years and above. This study aimed to investigate the relationship between long-term exposure to PM and the incidence of asthma in adults aged 45 years and above.

Methods: A cohort study based on the China Health and Retirement Longitudinal Study (CHARLS) database was conducted to investigate the long-term effects of PM on self-reported asthma incidence in adults aged 45 years and above in China from 2011 to 2018. The PM concentrations were estimated using a high-resolution (1 km) satellite-based spatiotemporal model. A covariate-adjusted generalized linear mixed model was used to analyze the relationship between long-term exposure to PM and the incidence of asthma. Effect modifications and sensitivity analysis were conducted.

Results: After a 7-year follow-up, 103 (1.61 %) of the 6400 participants developed asthma. Each 10 μg/m increment in the 1-, 2-, 3-, and 4-year moving average concentrations of PM corresponded to a 1.82 [95 % confidence interval (CI):1.11-2.98], 1.95 (95 % CI: 1.24-3.07), 1.95 (95 % CI: 1.26-3.03) and 1.88 (95 % CI: 1.26-2.81) fold risk for incident asthma, respectively. A significant multiplicative interaction was observed between socioeconomic level and long-term exposure to PM. Stratified analysis showed that smokers and those with lower socioeconomic levels were at higher risk of incident asthma related to PM. Restricted cubic splines showed an increasing trend in asthma incidence with increasing PM. Sensitivity analyses showed that our model was robust.

Conclusion: Long-term exposure to PM was positively associated with incident asthma in middle-aged and elderly individuals. Participants with a history of smoking and lower socioeconomic levels had a higher risk. More studies are warranted warrant to establish an accurate reference value of PM to mitigate the growing asthma burden.