Effects of PM_2.5 components on hypertension and diabetes: Assessing the mitigating influence of green spaces

Particulate matter with diameters ≤2.5 μm (PM_2.5) is a significant air pollutant associated with hypertension and diabetes. However, the specific contributions of its components and their joint exposure with green spaces remain poorly understood, especially in developing regions.

This study aims to investigate the individual and joint impacts of PM_2.5 and its components on the middle-aged and older adults, identify primary risk factors, and assess disease risks associated with simultaneous exposure to green spaces.

We conducted a prospective cohort study in Tianjin from 2014 to 2021, involving individuals aged ≥45 years. Satellite-based machine learning models quantified PM_2.5 components, including black carbon (BC), organic matter (OM), sulfate (SO₄^2-), nitrate (NO₃^-), ammonium (NH₄⁺), and chloride (Cl^-). Residential greenness was assessed using the Normalized Difference Vegetation Index (NDVI). A time-varying Cox proportional hazards model analyzed associations between PM_2.5 components and the incidence of hypertension and diabetes. The quantile g-computation model evaluated joint exposure effects and relative contributions of the components. Pollutants and NDVI were dichotomized using median values and combined to create a joint exposure model, aimed at exploring the potential effects of NDVI. Stratified analyses were performed to identify vulnerable subpopulations.

Over 241,528.73 person-years of follow-up, there were 15,747 (38.34 %) new cases of hypertension and 8945 (13.59 %) new cases of diabetes. Each standard deviation (SD) increase in OM was associated with increased incidence of hypertension (hazard ratio: 1.609; 95 % confidence interval: 1.583, 1.636) and diabetes (1.484; 1.453, 1.515). Joint exposure to components is linked to higher incidence of hypertension and diabetes, with OM identified as the primary contributor. The joint exposure model indicated elevated population risk in areas with low NDVI and high PM_2.5 concentrations, particularly affecting males and individuals younger than 60 years.

Long-term exposure to higher levels of PM_2.5 components is significantly associated with increased hypertension and diabetes, with OM potentially being the primary contributor. Joint exposure to green space may mitigate these risks. These findings highlight how PM_2.5 sources impact health, informing more effective governance measures.