Associations between greenness and blood pressure and hypertension in Chinese middle-aged and elderly population: A longitudinal study

Greenness is an emerging modifiable environmental factor of high blood pressure and hypertension. However, current evidence is inconsistent, and high-quality studies are urgently needed, especially in developing country with high disease burden of hypertension. A longitudinal study was designed and 9,649 participants (aged ≥45 years) with 22,854 number of visits among three waves between 2011 and 2015 were included based on the China Health and Retirement Longitudinal Study. Long term greenness exposure was assessed by annual normalized difference vegetation index (NDVI). Linear and generalized linear mixed effect models were used to estimate the associations between greenness and blood exposure level and hypertension risk, respectively. The median NDVI level was 0.51, with a range from 0.09 to 0.74. An interquartile range (0.15) increase in NDVI was related to 1.05 mmHg reduction (95% CI: −1.65, −0.45) of systolic blood pressure, 0.72 mmHg reduction (95% CI: −1.06, −0.37) of diastolic blood pressure, and 12% (95% CI: 1%, 22%) lower odds of hypertension risk. The association of greenness and blood pressure was significantly stronger in the younger (<60 years) than in the older (≥60 years), and partially mediated by body mass index. These findings highlight the protective effect of greenness on blood pressure and hypertension in Chines middle-aged and elderly population, especially in the younger (<60 years), and suggest policy makers to take greenness level into special consideration in the process of urbanization.