Long-term exposure to ambient fine particles associated with asthma: A cross-sectional study among older adults in six low- and middle-income countries

Background: Ambient PM2.5 is considered harmful to the respiratory system. However, little has been shown about the long-term association between ambient PM2.5 and asthma. Methods: A survey from 2007 to 2010 was conducted among adults over 50 years of age in six low- and middle-income countries (including China, India, Ghana, Mexico, Russia, and South Africa), which belonged to one part of a prospective cohort study - the Study on global AGEing and adult health. The yearly mean PM2.5 concentrations of the residential communities of participants were estimated from remote sensing data. A mixed effects model was applied to investigate the association between ambient PM2.5 and asthma. Results: A total of 4553 asthma patients were identified among the 29,249 participants in this study, producing a prevalence of 15.57%. For each 10 mu g/m(3) increase in PM2.5, the adjusted prevalence ratio of asthma was 1.05 (95% Confidence Interval: 1.01, 1.08) after controlling for the effects of sex, age, BMI, education attainment, smoking status, alcohol consumption, and occupational exposure. Further analyses showed that males and smokers might be particularly vulnerable populations. Additionally, it was estimated that about 5.12% of the asthma cases in the study population (95% Confidence Interval: 1.44%, 9.23%) could be attributed to long-term PM2.5 exposure. Conclusion: Long-term exposure to PM2.5 might be an important risk factor of asthma. Effective air pollution reduction measures should be taken to reduce PM2.5 concentrations in order to reduce the associated asthma cases and disease burden.