Cardiometabolic Benefits of Residential Green Space

Takeaways from 3 publications based on a large cross-sectional study

By Kurt Beil, ND, LAc, MPH

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References

All 3 publications are derived from the 33 Communities Chinese Health Study

  1. Yang B-Y, Markevych I, Bloom MS, et al. Community greenness, blood pressure, and hypertension in urban dwellers: The 33 Communities Chinese Health Study. Environ Int. 2019;126:727-734.
  2. Yang B-Y, Markevych I, Heinrich J, et al. Residential greenness and blood lipids in urban-dwelling adults: The 33 Communities Chinese Health Study. Environ Pollut. 2019;250:14-22.
  3. Yang B-Y, Markevych I, Heinrich J, et al. Associations of greenness with diabetes mellitus and glucose-homeostasis markers: The 33 Communities Chinese Health Study. Int J Hyg Environ Health. 2019;222(2):283-290.

Study Objective

To determine the impact of residential green space (RGS) on biomarkers of cardiometabolic health

Design

Cross-sectional study

Participants

Respondents to the 33 Communities Chinese Health Study (33CCHS) survey and biomonitoring project in 11 districts in each of 3 different cities in Liaoning province, northeast industrialized China in 2009. Participants (N=24,845) were 18-74yo with no pre-existing severe illnesses or history of illness directly related to the collected biomarkers. Blood serum was drawn in a subset of n=15,477.

Study Parameters Assessed

RGS was determined by Normalized Difference Vegetation Index (NDVI) satellite data, a common method for assessing green-space type and distribution. A spatial analysis was performed for the RGS score within a 500m radius (NDVI500) around the participants’ residential address and their biomarker data.

Local air pollution (PM2.5 and NO2) data and survey questions about current physical activity levels were included in the statistical models.

Outcome Measures

Standard markers of cardiometabolic health (sometimes referred to as allostatic load) were collected, including:

  • Systolic (SBP) and diastolic (DBP) blood pressure
  • Total cholesterol (TC), triglycerides (TG), LDL, HDL
  • Fasting & 2-hour post-prandial (PP) glucose, insulin, HOMA-IR, HOMA-B
  • Body mass index (BMI)

Key Findings

RGS was inversely associated with many of the cardiometabolic biomarkers collected. After controlling for age, sex, ethnicity, household income, district-average GDP, tobacco use, alcohol use, exercise level, soft drink consumption, diet, and family history of dyslipidemia, the data showed that a 0.1 unit NDVI500 increase was significantly (P<0.05) associated with:

  • Reduction of risks of hypertension and Type II diabetes mellitus by 5% and 12%, respectively
  • Reduction of SBP by 0.82 mmHg
  • Reduction of TC, TG and LDL levels by 1.52%, 3.05% and 1.91%, respectively
  • Increase in HDL level by 0.52%
  • Reduction of fasting glucose, 2hr PP glucose, 2hr PP insulin, and HOMA-IR by 1.14%, 2.03%, 1.66%, and 1.17%, respectively
  • Increase in HOMA-B by 3.33%

Factors regarding air pollution, BMI, and physical activity mediated some, but not all, of these results, demonstrating that there are other health effects of green space.

Practice Implications

These results show that green space around a person’s home is positively associated with improved cardiometabolic measures of blood pressure, blood lipids, and blood sugar and insulin response. This is one of the first large-scale studies (divided across 3 publications) to identify a direct association between green space in the proximal living environment and improvements in biomarkers of cardiovascular and metabolic health.

While a previous review of NDVI studies demonstrated that higher RGS levels were associated with multiple benefits to human health, this is one of the first times that biomarkers have been collected and analyzed in relation to access to green space.1 This study supports a meta-analysis demonstrating that acute exposure to green space has a beneficial effect on cardiometabolic markers of health.2

This is one of the first large-scale studies…to identify a direct association between green space in the proximal living environment and improvements in biomarkers of cardiovascular and metabolic health.

Since this study controlled for diet and exercise, the findings reflect other influences on the outcome health measures. Similarly, income, use of tobacco and alcohol, and other socioeconomic measures were also factored into the analysis to exclude potential effects of lifestyle.

In their now-classic paper, Hartig and coworkers3 stated that the health benefits of being exposed to green spaces fall under 1 of 4  broad categories:

  • Physical activity
  • Air quality
  • Stress reduction and mental health
  • Social engagement

Physical activity

Physical activity is well-known to positively affect cardiometabolic health. Studies have demonstrated that access to green space (e.g., parks, ball fields, hiking trails) encourages more physical activity, which is associated with improved health outcomes.4 Since the current study controlled for physical activity, even though more physical activity did occur in areas of greater RGS, this activity was not responsible for the findings observed.

Air quality

Similarly, air quality is known to impact cardiometabolic health.5 Exposure to airborne particulate matter is associated with cardiovascular disease (CVD) and increased inflammatory markers.6 The authors of the current study have published data showing similar effects on blood glucose measures.7

Vegetation is known to filter airborne pollutants, improving air quality and decreasing rates of disease.8 However, as with physical activity, the current study controlled for the effects of pollution, and thus there must be some other explanation for these results.

One benefit may be the vegetative production of salutogenic (health-promoting) chemicals, such as phytoncides, which have been studied extensively for their immune-stimulating properties.9,10 At least 1 study has demonstrated that shinrin-yoku (the “forest bathing” activities that are the source of phytoncide research) has beneficial effects on blood glucose.11 It is possible that the trees and plants in our residential communities produce airborne chemicals that benefit our physiology.

Stress reduction and mental health

One of the most studied areas of the health effects of green spaces is their capacity to modulate the psychophysiological stress response. Many systematic reviews and meta-analyses have shown that both short- and long-term exposure to natural environments have beneficial effects on physical and mental states, via cognitive, affective, and neuroendocrine mechanisms.12-14 Natural settings are inherently relaxing and restorative, consistent with the evolutionary “Biophilia Hypothesis” of E.O. Wilson, and help our bodies and minds maintain healthy homeostatic function.15

The cardiometabolic markers used in the current study are some of the most common for assessing baseline physiologic status and are often included as component measures of the allostatic load.16 While other studies have demonstrated that green space has beneficial effects on allostatic load, this is one of the first to do so on such a large scale.17

Social engagement

Humans are social beings, and individual health is determined in part by the quality and quantity of social interactions. The relationship between social isolation and CVD is well-established18 and diabetes has recently been investigated as a sequela of loneliness, possibly via the same neuro-endocrine and inflammatory mechanisms as for CVD.19

The fact that people come together at parks and other green spaces for social activities is also well-established.20,21 Recently, several studies have shown that the social-generating potential of green spaces translate into improved health for local residents.22 The current study did not consider social interactions, but these may have had unmeasured effects that contributed to the results.

Conclusion

Research on the effects of exposure to a natural environment increasingly shows health benefits in every area in which studies are conducted. Encouraging the creation and use of green space in urban settings is a valid approach to improving health-related biomarkers and reducing the burden of disease, as reflected by the cardiovascular and metabolic disease markers presented in this study. Clinicians, public health advocates, park departments, urban planners, and municipal officials should use this information to advocate for the inclusion of green space in a comprehensive health-promotion strategy.

About the Author

Kurt Beil, ND, LAc, MPH is a naturopathic and Chinese medicine practitioner in New York’s lower Hudson Valley region. He completed his postdoctoral research at National University of Natural Medicine’s Helfgott Research Institute, where he focused on biomarker and psychometric assessment of the restorative and therapeutic effect of natural environments. He holds a master’s degree in public health focused on the benefits of green space as a sustainable public health promotion tool, and speaks and writes regularly about these topics. Beil also maintains a Facebook group (“Naturopaths for Nature”) about the health benefits of contact with nature. He can be reached at drkurt@earthlink.net or www.hudsonvalleynaturalhealth.com.

References

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