Associations between long-term exposure to PM2.5 chemical constituents and allergic diseases: evidence from a large cohort study in China

Abstract

Background: Exposure to air pollutants may cause immune responses and further allergic diseases, but existing studies have mostly, if not all, focused on effects of short-term exposure to PM_2.5 on allergic diseases.

Objectives: We estimated associations of long-term exposure to PM_2.5 chemical constituents with allergic disease risks and effect modification.

Methods: We used the baseline of a newly established, provincially representative cohort of 51,480 participants in southwest China. The presence of allergic rhinitis, allergic asthma, urticaria, and allergic conjunctivitis was self-reported by following a formed questionnaire in face-to-face interviews. The average concentrations of PM_2.5 chemical constituents (NO₃^-, SO₄^2-, NH₄⁺, organic matter [OM], and black carbon [BC]) over participants' residence were estimated using machine learning models. Logistic regression with double robust estimator and weighted quantile sum regression were used to estimate the effects of PM_2.5 chemical constituents on allergic disease risks, as well as relative importance of each PM_2.5 chemical constituent.

Results: Per interquartile range increase in the concentration of all PM_2.5 chemical constituents was associated with the elevated risks for allergic asthma (OR = 1.79 [1.41-2.26]), allergic conjunctivitis (1.54 [1.19-2.00]), urticaria (1.36 [1.25-1.48]), and allergic rhinitis (1.18 [1.11-1.26]). NO₃^- contributed more to risks for allergic asthma (weight = 46.05 %), urticaria (72.29 %), and allergic conjunctivitis (47.65 %), while NH₄⁺ contributed more to allergic rhinitis (78.07 %). OM contributed most to the risks for allergic asthma (30.81 %) and allergic conjunctivitis (31.40 %). BC was also associated with allergic rhinitis, urticaria, and allergic conjunctivitis, only with a considerable weight for urticaria (24.59 %). Joint effects of PM_2.5 chemical constituents on risks for allergic rhinitis and urticaria were stronger in minorities and farmers than their counterparts.

Conclusion: Long-term exposure to PM_2.5 chemical constituents was associated with the increased allergic disease risks, with NO₃^- and NH₄⁺ accounting for the largest variance of the associations. Our findings would serve as scientific evidence for developing more explicit strategies of air pollution control.

Keywords: Allergic asthma; Allergic conjunctivitis; Allergic rhinitis; Ammonium; Black carbon; Nitrate; Organic matter; PM(2.5); Sulfate; Urticaria.