Air pollution is linked to cognitive decline independent of hypersensitive C-reactive protein: insights from middle-aged and older Chinese.

Abstract

Background: Long-term air pollution exposure and inflammation are considered to be associated with cognitive decline. However, whether air pollution exposure related cognitive decline is dependent on inflammation remains uncertain.

Materials and methods: The present study collected data from China Health and Retirement Longitudinal Study (CHARLS) at baseline in 2011, with a follow up period in 2015. Concentration of air pollutants (particles with diameters ≤ 1.0 μm [PM₁], ≤ 2.5 μm [PM_2.5], ≤ 10 μm [PM₁₀], nitrogen dioxide [NO₂] and ozone [O₃]) were obtained from China High Air Pollutants (CHAP) dataset. Hypersensitive C-reactive protein (hs-CRP), a systemic inflammation marker, was measured in blood of subjects and cognitive function was assessed by standardized questionnaire.

Results: A total of 6434 participants were included in the study. Lower exposure to PM_2.5, PM₁, PM₁₀ and NO₂ were associated with mitigated cognitive decline. The odds ratios (ORs) for air pollutants changes and cognitive decline and 95% confidence intervals (CIs) were as follows: PM_2.5-0.934(0.925, 0.943), PM₁- 0.945 (0.935,0.955), PM₁₀-0.977(0.972,0.982) and NO₂-0.962(0.950,0.975), respectively. Hs-CRP showed no significant correlation with cognitive decline or change in levels of air pollution. The interaction regression analyses, both unadjusted and adjusted, did not uncover any significant correlation between hs-CRP and air pollution with respect to cognitive decline. Bootstrap test exhibited no significant mediating effect of hs-CRP on the relationship between any air pollutants and cognitive decline, the indirect effects of hs-CRP in conjunction with exposure to different air pollutants were all found to be non-significant, with the following bootstrap CIs and p-values: PM_2.5-1.000([1.000,1.000], P = 0.480),PM₁-1.000([1.000,1.000], P = 0.230),PM₁₀-1.000([1.000,1.000], P = 0.650), O₃-1.000([1.000,1.000], P = 0.470), ΔNO₂-1.000([1.000,1.000], P = 0.830) .

Conclusion: Ambient air pollution exposure was linked to cognitive decline independent of hs-CRP level.