Particulate matter air pollution, physical activity and systemic inflammation in Taiwanese adults.

Background: The protective effects of physical activity (PA) against chronic disease can be partially ascribed to its anti-inflammatory effects. On the other hand, long-term exposure to particulate matter with an aerodynamic diameter less than 2.5μm (PM _2.5 ) may induce systemic inflammation.
Objective: To investigate the joint effects of habitual PA and long-term exposure to PM _2.5 on systemic inflammation in a large cohort of Taiwanese adults.
Methods: We studied 359,067 adult participants from a cohort consisting of Taiwanese residents who participated in a standard medical examination program from 2001 to 2014. Peripheral white blood cell (WBC) and differential counts were measured as indicators of systemic inflammation. Two-year average concentration of PM _2.5 was estimated at each participant's address using a satellite-based spatio-temporal model. Habitual PA level was assessed by questionnaire (inactive, low, moderate and high). Mixed-effects linear regression model was used to examine the associations of WBC counts with PM _2.5 and PA.
Results: Compared with inactive participants, those with low, moderate or high PA levels had 0.36% [95% confidence interval (CI): 0.31%, 0.41%], 0.70% (95%CI: 0.65%, 0.76%) and 1.16% (95%CI: 1.11%, 1.22%) lower WBC counts, respectively, after adjusting for PM _2.5 exposure and a wide range of confounders. Long-term PM _2.5 exposure was associated with increased WBC counts at all PA levels. Analyses for differential counts generated similar results. No significant interaction was observed between PA and PM _2.5 exposure (P for interaction=0.59).
Conclusions: Habitual PA was associated with statistically significant lower markers of systemic inflammation across different levels of PM _2.5 . Effects of PA and PM _2.5 exposure on systemic inflammation are independent.
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