Associations of Fine Particulate Matter Constituents with Metabolic Syndrome and the Mediating Role of Apolipoprotein B: A Multicenter Study in Middle-Aged and Elderly Chinese Adults

Fine particulate matter (PM2.5) was reported to be associated with metabolic syndrome (MetS), but how PM2.5 constituents affect MetS and the underlying mediators remains unclear. We aimed to investigate the associations of long-term exposure to 24 kinds of PM2.5 constituents with MetS (defined by five indicators) in middle-aged and elderly adults and to further explore the potential mediating role of apolipoprotein B (ApoB). A multicenter study was conducted by recruiting subjects (n = 2045) in the Beijing-Tianjin-Hebei region from the cohort of Sub-Clinical Outcomes of Polluted Air in China (SCOPA-China Cohort). Relationships among PM2.5 constituents, serum ApoB levels, and MetS were estimated by multiple logistic/linear regression models. Mediation analysis quantified the role of ApoB in "PM2.5 constituents-MetS" associations. Results indicated PM2.5 was significantly related to elevated MetS prevalence. The MetS odds increased after exposure to sulfate (SO42-), calcium ion (Ca2+), magnesium ion (Mg2+), Si, Zn, Ca, Mn, Ba, Cu, As, Cr, Ni, or Se (odds ratios ranged from 1.103 to 3.025 per interquartile range increase in each constituent). PM2.5 and some constituents (SO42-, Ca2+, Mg2+, Ca, and As) were positively related to serum ApoB levels. ApoB mediated 22.10% of the association between PM2.5 and MetS. Besides, ApoB mediated 24.59%, 50.17%, 12.70%, and 9.63% of the associations of SO42-, Ca2+, Ca, and As with MetS, respectively. Our findings suggest that ApoB partially mediates relationships between PM2.5 constituents and MetS risk in China.