The Effects of Greenness Exposure on Hypertension Incidence Among Chinese Oldest Old: A 10-Year Prospective Cohort Study

Abstract Background Present studies showed greenness affected hypertension incidence. While population-based epidemiologic studies are limited in the oldest-old population (aged 80+). Methods This was a 10-year prospective cohort study that included oldest old (80 years +) from the Chinese Longitudinal Healthy Longevity Survey (CLHLS). Participants were free of hypertension at baseline (2008) and were followed up at 2011/2012, 2014, and 2018 waves. The 1-year average of the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) at 16-Day 500 m buffer before the year of hypertension event occurrence or last interview (for censoring) was estimated at 652 counties/districts units level of the participants resided and as exposure indicator. The non-linear association between greenness and hypertension incidence was performed by the Cox proportional hazards model with the penalized spline. The links between greenness and hypertension incidence were performed by the random-effects Cox proportional hazards model adjusted for potential confounding variables. We also examined the causal mediation effects of BMI, leisure activity, and PM2.5 on the association between greenness exposure and hypertension. Results Among 5432 participants, the incidence of hypertension was 7.25 (95% CI: 6.83 to 7.67) per 100 person-years. We found a non-liner association existed between greenness exposure and hypertension risk. In the fully adjusted model, the third tertile of NDVI value presenting protective effects on hypertension incidence compared with the first tertile (hazard ratios (HRs): 0.51; 95% confidence interval: 0.40-0.64). The third tertile of EVI value had a significant protective effect on hypertension incidence, compared with participants in the first tertile (HRs:0.44, 95%CI: 0.34-0.55). The effect of greenness exposure on hypertension was more pronounced in participants living in central/western China. We observed there were 41.63% and 17.01% of the association between NDVI/EVI exposure and hypertension was mediated by PM2.5, respectively. Conclusions Greenness could decrease approximate 50% risk induced by hypertension among oldest-old people, that is, expanding greenness is a recommended approach to hypertension prevention for the them. In particular, implementing plans to expanding green space construction in central/western China is needed. It is also emphasized the the importance of improve air quality when greenness exposure is existing.