Associations of PM_2.5 composition and green space with metabolic syndrome in a Chinese essential hypertensive...

Metabolic syndrome (MetS) has emerged as a significant global public health concern. While environmental factors, including PM_2.5, have been identified as important risk factors for MetS in the general population, limited studies have investigated their impact on individuals with essential hypertension. Therefore, our study aims to explore the relationship between PM_2.5 composition, green space, and their combined effects on MetS among a Chinese essential hypertensive population.

A total of 20,131 participants diagnosed with essential hypertension from 10 provinces in China were included in this study. Individual level exposure to various environmental factors (including PM_2.5, PM_2.5 composition, green space and temperature) were evaluated using spatiotemporal models based on satellites data. Participants were defined as MetS according to the definition issued by the International Diabetes Federation. Generalized additive mixed models were used to analyze the individual air pollutants, green space and their interaction on MetS.

The prevalence of MetS in this population was 44.33%. The adjusted odd ratio (OR) of MetS, with each one unit increase in SO₄^2-, BC and NO₃^- were 1.077 (1.049, 1.106), 1.126 (1.077, 1.177) and 0.977 (0.958, 0.996) respectively. Additionally, each unit increase of the Normalized Difference Vegetation Index (NDVI) was associated with a decreased risk of MetS (OR: 0.988, 95% CI: 0.984-0.993). In particular, green space was found to mitigate the adverse impacts of PM_2.5 on MetS (OR: 0.988, 95% CI: 0.984-0.993).

Our results suggested that there was a positive association between PM_2.5 and its composition (SO₄^2-, BC) with MetS in the essential hypertensive population, while green space might play a protective role. Moreover, green space could effectively weaken the positive relationship between air pollutants and MetS, especially in males and participants younger than 60 years old.