Cardiometabolic benefits of residential green spaces

References

All 3 publications come from the 33 Communities Chinese Health Study

1. Yang BY, Markevych I, Bloom MS, et al. Gemeinschaftsgrün, Blutdruck und Bluthochdruck bei Stadtbewohnern: The 33 Communities Chinese Health Study. Umgebung Int. 2019;126:727-734.
2. Yang BY, Markevych I, Heinrich J, et al. Wohngrün und Blutfette bei in Städten lebenden Erwachsenen: The 33 Communities Chinese Health Study. Umweltverschmutzung. 2019;250:14-22.
3. Yang BY, Markevych I, Heinrich J, et al. Assoziationen von Grün mit Diabetes mellitus und Glukose-Homöostase-Markern: The 33 Communities Chinese Health Study. Int J Hyg Environ Health. 2019;222(2):283-290.

Study objective

Determining the influence of residential green space (RGS) on biomarkers of cardiometabolic health

Draft

Cross-sectional study

Participant

Respondents of the 33 Communities Chinese Health Study (33CCHS) survey and biomonitoring project in 11 counties in each of 3 different cities in Liaoning Province, northeastern industrialized China in 2009. Participants (N=24,845) were 18-74 years old and had no pre-existing major illnesses or medical history directly related with the collected biomarkers. Blood serum was collected in a subset of n = 15,477.

Study parameters assessed

RGS was determined using satellite data from the Normalized Difference Vegetation Index (NDVI), a common method for assessing green space type and distribution. For the RGS score, a spatial analysis was performed within a 500 m radius (NDVI500) of the participants' home 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.

Target parameters

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

• Systolischer (SBP) und diastolischer (DBP) Blutdruck
• Gesamtcholesterin (TC), Triglyceride (TG), LDL, HDL
• Nüchtern & 2 Stunden postprandial (PP) Glukose, Insulin, HOMA-IR, HOMA-B
• Body-Mass-Index (BMI)

Key insights

RGS was inversely associated with many of the cardiometabolic biomarkers collected. After controlling for age, gender, ethnicity, household income, county average GDP, tobacco consumption, alcohol consumption, physical activity, soft drink consumption, diet and family history of dyslipidemia, the data showed that a 0.1 unit increase in NDVI500 was significant (P<0.05) associated with:

• Reduzierung des Risikos für Bluthochdruck und Diabetes mellitus Typ II um 5 % bzw. 12 %
• Reduktion des SBP um 0,82 mmHg
• Senkung der TC-, TG- und LDL-Spiegel um 1,52 %, 3,05 % bzw. 1,91 %
• Erhöhung des HDL-Spiegels um 0,52 %
• Reduktion von Nüchternglukose, 2-Stunden-PP-Glukose, 2-Stunden-PP-Insulin und HOMA-IR um 1,14 %, 2,03 %, 1,66 % bzw. 1,17 %
• Steigerung von HOMA-B um 3,33 %

Factors related to air pollution, BMI and physical activity mediated some, but not all, of these results, showing that there are other health effects of green spaces.

Practice implications

These results show that green spaces around a person's home are positively associated with improved cardiometabolic measures of blood pressure, blood lipids, and blood glucose and insulin response. This is one of the first large-scale studies (divided into 3 publications) to identify a direct association between nearby green spaces and improvements in biomarkers of cardiovascular and metabolic health.

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

This is one of the first large-scale studies … to identify a direct association between green spaces in the local area and improvements in biomarkers of cardiovascular and metabolic health.

Because this study controlled for diet and exercise, the results reflect other influences on health parameters. Similarly, income, tobacco and alcohol consumption, and other socioeconomic metrics were also included in the analysis to rule out possible lifestyle effects.

In their now classic article Hartig and colleagues³stated that the health benefits of exposure to green spaces fall into one of four broad categories:

• Physische Aktivität
• Luftqualität
• Stressabbau und psychische Gesundheit
• Soziales Engagement

Physical activity

Physical activity is known to positively influence cardiometabolic health. Studies have shown that access to green spaces (e.g., parks, ball fields, walking trails) encourages greater physical activity, which is associated with improved health outcomes.⁴Because the current study controlled for physical activity, although more physical activity occurred in areas with greater RGS, this activity was not responsible for the observed results.

Air quality

Air quality is also known to influence cardiometabolic health.⁵Exposure to airborne particulate matter is associated with cardiovascular disease (CVD) and elevated inflammatory markers.⁶The authors of the current study have published data showing similar effects on blood glucose measurements.⁷

Vegetation is known to filter air pollutants, improve air quality and reduce disease rates.⁸However, as with physical activity, the current study controlled for the effects of pollution and therefore there must be another explanation for these results.

One advantage may be the vegetative production of salutogenic (health-promoting) chemicals such as phytoncides, which have been extensively studied for their immune-stimulating properties.^9.10At least 1 study has shown thisshinrin yoku(the “forest bathing” activities that are the source of phytoncide research) has positive effects on blood sugar.¹¹It is possible that the trees and plants in our living communities produce airborne chemicals that benefit our physiology.

Stress relief and mental health

One of the most studied areas of the health effects of green spaces is their ability 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.^12-14Natural environments are inherently relaxing and restorative, consistent with EO Wilson's evolutionary “biophilia hypothesis,” and help our bodies and minds maintain healthy homeostatic function.^fifteen

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

social commitment

Humans are social creatures, and individual health is determined in part by the quality and quantity of social interactions. The relationship between social isolation and CVD is well established¹⁸and diabetes has recently been studied as a consequence of loneliness, possibly through the same neuroendocrine and inflammatory mechanisms as in CVD.¹⁹

It is also well known that people come together in parks and other green spaces for social activities.^20.21Recently, several studies have shown that the social-creating potential of green spaces translates into improved health for residents.²²The 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 is increasingly showing health benefits in all areas where studies are conducted. Promoting the creation and use of green spaces in urban environments 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 administrators, urban planners, and community officials should use this information to advocate for the inclusion of green spaces in a comprehensive health promotion strategy.