Effect of Exposure to Natural Environment on Health Inequalities: An Observational Population Study
Research has established that low-income people tend to have higher mortality rates than high-income residents. This study across all of England demonstrates that this gap in mortality rate is about half the size in areas with the most green space compared to areas with the least green space.
This study is relevant to those interested in describing health inequalities across income, and the role of green space access in reducing those inequalities.
This study has the power of a large sample size and national-level coverage. It does, however, use some assumptions when aggregating these data, like taking the average income of an area and assuming all households have equal access to the green spaces in the area. Additionally, authors did not have access to data on the quality of that open space.
This study occurs in England, looking at the entire population younger than retirement age (366,348 records).
The study considers “green space,” defined as parks, open spaces, and agricultural land at least five square meters. It does not include home gardens.
The purpose of this study is to determine whether exposure to green space can help reduce health inequality between high- and low-income groups.
- In places with the least green space, low-income residents have 93 percent higher mortality rates compared to high-income residents, on average. In places with the most green space, low-income residents have 43 percent higher mortality rates.
- For circulatory disease, low-income residents have 119 percent higher incidence than high-income residents in places with the least green space. In places with the most green space, low-income residents have 54 percent higher mortality rates from circulatory diseases.
- The authors find no significant relationship between income, green space, and mortality from lung disease or self-harm.
- Across all income levels, mortality rates are about six percent lower for people living in areas with the most green space.
- The authors hypothesize that proximity to green space helps to increase residents’ physical activity, thus explaining lower overall mortality and mortality due to circulatory disease.
The authors identify the location of green space using the Generalized Land Use Database (GLUD) that classifies land use across England, with 10-square-meter resolution. The authors matched this to a spatial database of the share of low-income families in a given area.
The authors match the location of green space to national individual mortality records for 2001-2005, for all deaths of pre-retirement-age people, for 366,348 records. These records include the age at death, sex, and cause of death. In addition to overall death rates, the authors separately consider death from circulatory diseases, lung cancer, and self-harm, all of which are known to have strong connections with physical activity and income. The very large sample size allowed the authors to have a range of income levels with a range of exposure to green space.
The authors developed a statistical model predicting the number of deaths as a function of exposure to green space, controlling for age, sex, population density, average education in the area, and air pollution.
Mitchell, R. and Popham, F., 2008. Effect of exposure to natural environment on health inequalities: an observational population study. The Lancet 372(9650): 1655-1660.