Association Of Green Space And NO₂ Exposure With Hypertension Among Older Adults In China

Objective:Hypertension,as one of the major chronic non-communicable diseases,seriously threatens the physical and mental health of older adults which has become a major public health problem in China.The impact of environmental factors such as green space,atmospheric NO₂on hypertension has received widespread attention.This study aims to clarify the current situation of hypertension in the Chinese elderly and explore the association of green space,NO₂and their combined effect on hypertension of older adults,to provide a scientific basis for the prevention and treatment of hypertension.Methods:This study is a cross-sectional study of the 2017-2018 from the Chinese Longitudinal Healthy Longevity Survey in older adults in China,using a non-proportional target random sampling design method.A total of 15423 older adults aged 65 and above were included as the research subjects.Information such as demographic characteristics,lifestyle habits,and health status of the subjects was collected through questionnaire surveys.Blood pressure values of the subjects were measured through physical examination.Green space is represented by the Normalized Difference Vegetation Index（NDVI）.NDVI were measured by Moderate Resolution Imaging Spectrometer of National Aeronautics and Space Administration（NASA）.Data of NO₂derived from the Chinese surface air pollutant data set.Meteorological data acquisition using NASA’s MERRA-2 reanalysis data set.According to the residential address of the study subjects,the annual average concentrations of NDVI and NO₂within a radius of 1000 m near the residence of the past three years were matched as the exposure concentrations;furthermore,corresponding matching of the annual average temperature and humidity in the last three years was used to control for confounding factors.R 4.1.2 software is used for statistical description and analysis.Univariate analysis was used to analyze the influencing factors of hypertension in older adults.Multivariate logistic regression analysis was used to analyze the relationship between single exposure and combined exposure of NDVI,NO₂and hypertension in older adults.Subgroup analysis was used to clarify the relationship between NDVI,NO₂and hypertension in different subgroups.A restrictive cubic spline function was used to analyze the exposure-response relationship of NDVI,NO₂and hypertension in older adults.Interaction analysis was used to explicit the multiplicative and additive interaction effects of NDVI and NO₂on hypertension in older adults.Mediation effect analysis was used to explicit the mediating role of variables such as NO₂in the association path between NDVI and hypertension.Results:1.In this study,a total of 15423 older adults were included,with an average age of（85.6±11.6）years,the prevalence of hypertension was about 59.8%.Age,gender,marital status,education,economic status,smoking,exercise,dietary level,BMI,and diabetes may be the factors influencing hypertension in older adults.2.The results of the multivariate logistic regression single-exposure model showed that in the main model,NDVI was negatively associated with the risk of hypertension,with an OR（95%CI）value of 0.947（0.919～0.975）.Compared with the T₁group of NDVI,the risk of hypertension was lower in the T₃group[OR（95%CI）was 0.824（0.750～0.905）],and the trend test was statistically significant（P<0.05）.In the main model,NO₂showed a positive association with the risk of hypertension with increasing NO₂,with an OR（95%CI）value of 1.007（1.003～1.012）.Compared with the T₁group of NO₂,the T₂and T₃groups had a higher risk of hypertension[OR（95%CI）was 1.179（1.074～1.294）,1.298（1.169～1.441）,respectively],and the trend test was statistically significant（P<0.05）.3.The results of the multivariate logistic regression double-exposure model showed that in the main model,increasing NDVI was negatively associated with the risk of hypertension,with an OR（95%CI）value of 0.960（0.929～0.993）.Compared with the T₁group of NDVI,the T₃had a lower risk of hypertension[OR（95%CI）was 0.856（0.774～0.948）],and the trend test was statistically significant（P<0.05）.In the main model,the association between the continuous variable NO₂and hypertension was not statistically significant（P>0.05）.4.The results of subgroup analysis showed that the association of NDVI and hypertension was statistical significantly（P<0.05）in the older adults of 65～79 years,male,living in towns,ethnic han,different marital status,different education status,medium economic status,living far from traffic road within 100 m,never drinking,never exercise,activity of daily living is normal,instrumental activity of daily living is abnormal,normal weight,no diabetes,shows that NDVI has a negative association with hypertension in older adults.The association of NO₂and hypertension was statistical significantly（P<0.05）in the older adults of 90～99 years,female,living in south,ethnic han,uneducated,rich economic status,never smoking,exercising,overweight or obesity,self-health evaluation are general,shows that NO₂has a positive association with hypertension in older adults.5.The restricted cubic spline analysis showed a linear relationship between NDVI and hypertension in older adults(P_{overall association}<0.001,P_nonlinearity=0.338),a nonlinear relationship between NO₂and hypertension in older adults(P_{overall association}<0.001,P _nonlinearity<0.001).6.The interaction results showed that the multiplicative interaction between NDVI and NO₂on hypertension was significant[OR（95%CI）was 1.005（1.003～1.008）].The additive interaction of NDVI and NO₂on hypertensive in older adults was not significant.7.The mediation effect results showed that BMI had a mediation effect in the association of NDVI and hypertension in older adults,accounting for 9.1%of the total effect.The combined effect of NO₂and BMI plays a chain mediating effect in the association of NDVI and hypertension in older adults;NO₂or exercise has no mediating role in the association between NDVI and hypertension of older adults.Conclusions:1.With the increase of NDVI level,NDVI is negatively and linearly associated with the risk of hypertension in older adults.2.When NO₂concentration is high,NO₂is positively and nonlinearly associated with the risk of hypertension in older adults with the increase of NO₂concentration.3.NDVI and NO₂may have interaction on hypertension of older adults.4.BMI may have a mediating effect in the association between NDVI and hypertension in older adults.The co-effect of NO₂and BMI may have a chain mediating effect in the association between NDVI and hypertension in older adults.