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. 2022 Jul 11;21(1):66.
doi: 10.1186/s12940-022-00876-6.

The effects of greenness exposure on hypertension incidence among Chinese oldest-old: a prospective cohort study

Zhou Wensu  1 , Wang Wenjuan  1 , Zhou Fenfen  1 , Chen Wen  2 , Ling Li  3
Affiliations

The effects of greenness exposure on hypertension incidence among Chinese oldest-old: a prospective cohort study

Zhou Wensu et al. Environ Health. .

Abstract

Background: Although the oldest-old (those aged over 80 years) are vulnerable to environmental factors and have the highest prevalence of hypertension, studies focusing on greenness exposure and the development of hypertension among them are insufficient. The aim of this study was to explore the association between residential greenness and hypertension in the oldest-old population.

Methods: This cohort study included data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS). The oldest-old were free of hypertension at baseline (2008), and hypertension events were assessed by follow-up surveys in 2011, 2014, and 2018. The one-year averages of the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) at 500-m buffer before the interview year of incident hypertension or last censoring interview were collected at the level of 652 residential units (district or county). The linear or nonlinear association between greenness and hypertension incidence was analyzed using the Cox proportional hazards model with penalized splines. The linear links between greenness and hypertension incidence were determined using the Cox proportional hazards model included a random effect term.

Results: Among 5253 participants, the incidence rate of hypertension was 7.25 (95% confidence interval [CI]: 6.83-7.67) per 100 person-years. We found a nonlinear association between greenness exposure and hypertension risk, and the exposure-response curve showed that 1 change point existed. We examined the linear effect of greenness on hypertension by categorizing the NDVI/EVI into low and high-level exposure areas according to the change point. We found more notable protective effects of each 0.1-unit increase in greenness on hypertension incidence for participants living in the high-level greenness areas (hazard ratio (HR) = 0.60; 95% CI: 0.53-0.70 for NDVI; HR = 0.46; 95% CI: 0.37-0.57 for EVI). In contrast, no significant influence of greenness exposure on hypertension risk was found for participants living in the low-level greenness areas (HR = 0.77; 95% CI: 0.38-1.55 for NDVI; HR = 0.73; 95% CI: 0.33-1.63 for EVI).

Conclusions: Greenness exposure is nonlinearly associated with hypertension risk among the oldest-old, presenting its relationship in an inverse "U-shaped" curve. Greenness is a protective factor that decreases the risk of hypertension.

Keywords: China; Cohort study; Greenness; Hypertension; Oldest-old population.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Flow diagram of study including a group of people aged ≥80 years
Fig. 2
Fig. 2
Distributions of greenness indices on 652 units at baseline for 5253 participants. a NDVI and b EVI
Fig. 3
Fig. 3
Association of NDVI and hypertension incidence risk in Cox models with penalized splines (0.30: reference). Adjusted for age, living arrangement, PM2.5 concentration, regions, residence, gender, smoking, drinking, exercising, pension, marital status, education attainment, self-reported diabetes, personal outdoor activities, gardening, and BMI
Fig. 4
Fig. 4
Association of EVI and hypertension incidence risk in Cox models with penalized splines (0.21: reference). Adjusted for age, living arrangement, PM2.5 concentration, regions, residence, gender, smoking, drinking, exercising, pension, marital status, education attainment, self-reported diabetes, personal outdoor activities, gardening, and BMI
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