The association of hypertension and prehypertension with greenness and PM2.5 in urban environment

Background: The interplay of air pollution and urban greenness on hypertension (HTN) is not fully understood. Methods: We conducted a cross-sectional study to explore the role of greenness and PM2.5 on HTN for 40,375 adult res-idents in the New Taipei City, Taiwan. Normalized Difference Vegetation Index (NDVI) defined greenness and land use regression derived exposures of PM2.5 were used to calculate odds ratios (ORs) of HTN in logistic regression models and common OR of normal to stage 3 HTN in ordinal logistic regression models. Linear regression model was used to evaluate the association between NDVI and blood pressures, including systolic (SBP), diastolic (DBP) and mean (MBP) pressures. The mediation and moderation analysis were used to assess the mediation and moderation effect of PM2.5 on the association between greenness and SBP. Results: We found 37.3%, 21.4%, 8.2% and 2.7% of prehypertension and stage 1-3 hypertensions, respectively, for our study participants with annual PM2.5 exposures of 10.96-43.59 mu g/m(3) living in an urban environment with NDVI within 500 m buffer ranging from -0.22 to 0.26. The ORs of HTN were 0.744 (95% CI: 0.698-0.793) for NDVI (quar-tile 4 vs. quartile 1) and 1.048 (1.012-1.085) for each IQR (8.69 mu g/m(3)) increase in PM2.5, respectively. The common OR of the higher level of 5 categories of BP was 1.1310 (1.241-1.383). With each IQR increase of NDVI (0.03), we found SBP, DBP and MBP were decreased by 0.78 mm Hg (-0.93-0.64), 0.52 mm Hg (-0.62-0.43) and 0.61 mm Hg (-0.71-0.51), respectively, in linear regression models. Stratified analysis found greenness effect was more prom-inent for people who are younger, female, never smoking, and without chronic diseases. PM2.5 is moderated rather than mediated the association between greenness and SBP. Conclusions: Greenness was associated with lower prevalence of prehypertension and all stages of HTN and this relationship was moderated by PM2.5.