Association between annually locality-level exposure to PM10 and adult-onset asthma with factors related to lifestyle; extended Cox proportional hazard model

Abstract

Background:A number of studies have shown PM10 is associated with asthma in adults. However, most of those conducted either without or with few factors related to lifestyle. Aims:We estimated associations between annually locality-level PM10 and adult-onset asthma with factors indicating individual lifestyles including smoking, body mass index, basic livelihood security recipient, yearly income level, moderate physical activity and educational level. Methods:We employed 2008 Korean Community Health Survey providing individual information including physician diagnosed asthma. To determine subjects’ individual exposure, annual PM10 values as community level were extracted from Annual Report of Ambient Air Quality in Korea. Applied to risk of asthma, extended Cox proportional hazards model were used in retrospective way. All subjects were thought as if they began being in follow-up simultaneously. PM exposure, age and smoking were treated as time-dependent variable. Sex and the lifestyle factors were also considered in the model. Results:The risk of PM10 was 0.992 (95% CI: 0.981-1.003) in men and 1.001 (0.992-1.011) in women while both that of age and smoking (daily average cigarettes per year) showed a statistically significant association with greater asthma onsets. BMI was positively associated in women (1.105, 1.084-1.125); however, it was negatively associated in men (0.965, 0.940-0.992). Those who received basic livelihood security service were found being in significantly higher risk of being the asthmatics. Higher yearly income level was significantly associated to lower asthma incidence. Moderate physical activity didn’t have effect on the incidence. Educational level decreased the risk of adults onset asthma among men (P for trend=0.0184). Conclusions:Although our results are not statistically significant in association of PM10 with asthma-onset in adult, we suggest a couple of lifestyle factors can affect in this association. Our study results may not avoid a bias from measurement error on the estimation of the PM10 exposure level.