Long-Term Exposure to Air Pollution and the Occurrence of Metabolic Syndrome and Its Components in Taiwan

Abstract

Background: Metabolic syndrome (MetS), a major contributor to cardiovascular and metabolic diseases, has been linked with exposure to air pollution. However, the relationship between air pollutants and the five components of MetS [abdominal obesity, elevated triglyceride, decreased high-density lipoprotein cholesterol (HDL-C), elevated blood pressure, and elevated fasting blood glucose levels], has not been clearly described.

Objective: We examined the association between long-term exposure to air pollutants and the occurrence of MetS and its components by using a longitudinal cohort in Taiwan.

Methods: The MJ Health Research Foundation is a medical institute that conducts regular physical examinations. The development of MetS, based on a health examination and the medical history of an MJ cohort of 93,771 participants who were enrolled between 2006 and 2016 and had two or more examinations, was compared with estimated exposure to air pollutants in the year prior to health examination. The exposure levels to fine particulate matter [PM with an aerodynamic diameter of $\le 2.5\mu m$ (${\mathrm{PM}}_{2.5}$)] and nitrogen dioxide (${\mathrm{NO}}_2$) in the participants' residential areas were estimated using a hybrid Kriging/land-use regression (LUR) model executed using the XGBoost algorithm and a hybrid Kriging/LUR model, respectively. Cox regression with time-dependent covariates was conducted to estimate the effects of annual air pollutant exposure on the risk of MetS and its components.

Results: During the average follow-up period of 3.4 y, the incidence of MetS was 38.1/1,000 person-years. After mutual adjustment and adjustments for potential covariates, the results indicated that every $10\text{-}{\mu g/m}^3$ increase in annual ${\mathrm{PM}}_{2.5}$ concentration was associated with an increased risk of abdominal obesity [$\text{adjusted hazard ratio}\left(\text{aHR}\right)=1.07$; 95% confidence interval (CI): 1.01, 1.14], hypertriglyceridemia ($\text{aHR}=1.17$; 95% CI: 1.11, 1.23), low HDL-C ($\text{aHR}=1.09$; 95% CI: 1.02, 1.17), hypertension ($\text{aHR}=1.15$; 95% CI: 1.09, 1.21), and elevated fasting blood glucose ($\text{aHR}=1.15$; 95% CI: 1.10, 1.20). Furthermore, ${\mathrm{PM}}_{2.5}$ and ${\mathrm{NO}}_2$ may increase the risk of developing MetS among people who already "have" some components of MetS.

Discussion: Our findings suggest that in apparently healthy adults undergoing physical examination, exposure to ${\mathrm{PM}}_{2.5}$ and ${\mathrm{NO}}_2$ might be associated with the occurrence of MetS and its components. https://doi.org/10.1289/EHP10611.