Elsevier

The Lancet

Volume 372, Issue 9650, 8–14 November 2008, Pages 1655-1660
The Lancet

Articles
Effect of exposure to natural environment on health inequalities: an observational population study

https://doi.org/10.1016/S0140-6736(08)61689-XGet rights and content

Summary

Background

Studies have shown that exposure to the natural environment, or so-called green space, has an independent effect on health and health-related behaviours. We postulated that income-related inequality in health would be less pronounced in populations with greater exposure to green space, since access to such areas can modify pathways through which low socioeconomic position can lead to disease.

Methods

We classified the population of England at younger than retirement age (n=40 813 236) into groups on the basis of income deprivation and exposure to green space. We obtained individual mortality records (n=366 348) to establish whether the association between income deprivation, all-cause mortality, and cause-specific mortality (circulatory disease, lung cancer, and intentional self-harm) in 2001–05, varied by exposure to green space measured in 2001, with control for potential confounding factors. We used stratified models to identify the nature of this variation.

Findings

The association between income deprivation and mortality differed significantly across the groups of exposure to green space for mortality from all causes (p<0·0001) and circulatory disease (p=0·0212), but not from lung cancer or intentional self-harm. Health inequalities related to income deprivation in all-cause mortality and mortality from circulatory diseases were lower in populations living in the greenest areas. The incidence rate ratio (IRR) for all-cause mortality for the most income deprived quartile compared with the least deprived was 1·93 (95% CI 1·86–2·01) in the least green areas, whereas it was 1·43 (1·34–1·53) in the most green. For circulatory diseases, the IRR was 2·19 (2·04–2·34) in the least green areas and 1·54 (1·38–1·73) in the most green. There was no effect for causes of death unlikely to be affected by green space, such as lung cancer and intentional self-harm.

Interpretation

Populations that are exposed to the greenest environments also have lowest levels of health inequality related to income deprivation. Physical environments that promote good health might be important to reduce socioeconomic health inequalities.

Funding

None.

Introduction

The persistence and growth of socioeconomic health inequalities continues to command the attention of researchers, clinicians, and politicians.1, 2, 3, 4 Several studies have investigated how socioeconomic inequalities in health vary between societies, to try to establish what types of social and economic policies might reduce health inequalities.5, 6, 7, 8 Elsewhere in public-health research, interest is growing in how social and physical environments might interact to affect health, both in a salutogenic (ie, health improving) and pathogenic sense.9, 10 In this Article, we combine these strands of research.

How natural environments, or so-called green spaces, might affect health and health-related behaviour has received substantial attention from a range of disciplines, including epidemiology and psychology.11, 12, 13, 14, 15, 16, 17, 18 Green spaces are defined as “open, undeveloped land with natural vegetation”19 and include parks, forests, playing fields, and river corridors, for example. Evidence suggests that contact with such environments has independent salutogenic effects20—eg, green spaces independently promote physical activity.17, 21 Importantly, physical activity in such environments might have greater psychological and physiological benefits than might physical activity in other settings.22, 23 However, the effect of green space is not solely based on promotion or enhancement of physical activity. Several studies have shown that contact (either by presence or visual) with green spaces can be psychologically and physiologically restorative, reducing blood pressure and stress levels,13, 22 and possibly promoting faster healing in patients after surgical intervention.24

Although many studies show that natural environments enhance health or encourage healthy behaviours, and a few examine variation in these effects by socioeconomic status,11, 15, 18 the potential for access to green environments to affect socioeconomic inequality in health within populations has, as far as we are aware, received no attention.

We postulated that socioeconomic inequalities in health will be less pronounced in people with greater exposure to green space than in those with less exposure. The reason for this hypothesis is that some pathways, through which lower socioeconomic position might lead to worse health, are potentially modified by exposure to green space. We know, for example, that people with low socioeconomic status are less likely to exercise25 than are those with high socioeconomic status, partly because the environments in which they live are less conducive to it.26 Indeed, evidence for the relations between socioeconomic status and green space suggests that, although more deprived populations might be less likely to have access to such areas (by virtue of residential location or transportation disadvantage), socioeconomic position itself does not independently affect use of green space if it is readily available.18 Thus, disadvantaged populations that do have access to green space might be expected to accrue health benefits from using it (perhaps to a greater extent than any physical activity in other settings),22, 23 and therefore potentially enjoy better health than might those of a similar level of deprivation, but without access to green space.

Another pathway through which green space might be associated with lower inequality involves the physiological responses to the stress of poverty, which are implicated in increased risk of various diseases, notably heart disease.27, 28, 29, 30 If, as already noted, contact with natural environments is associated with reductions in stress, blood pressure, and promotion of healing,13, 22, 31 more deprived populations with access to green space might plausibly have some protection from the biological effects of their poverty-related stress, decreasing their mortality rates compared with those without access to green space. Thus we would expect inequalities in health to be reduced for populations who are exposed to green space in terms of causes of death for which there is a causal pathway on which green space might plausibly exert an effect.

These ideas prompted us to investigate whether the magnitude of income-related health inequality varies by exposure to green space.

Section snippets

Study design

We compared income-related health inequality in populations living in areas of England that are characterised by differing amounts of green space, with adjustment for other potentially confounding characteristics of the areas. We selected causes of death with contrasting causes to improve testing of our hypotheses and guard against residual confounding. This study was undertaken in July–August, 2008.

Data

We obtained data describing the quantity of green space in an area from the generalised land use

Results

We noted that people with greater exposure to green space were more likely to be less deprived than were those with little exposure to such areas (r2=−0·28, p<0·0001). However, with such a large study, we still had a substantial population who were exposed to each possible combination of deprivation and green space. The smallest population group was that living in areas that were classified as the most deprived (income-deprivation quartile 4) and the most green (group 5 of exposure to green

Discussion

Our study has shown that, in line with our hypothesis, the inequality in all-cause and circulatory disease mortality related to income deprivation is lower in populations who live in the greenest areas than in those who have less exposure to green space. We also noted an independent association between residence in the most green areas and decreased rates for all-cause and circulatory mortality.

Published work suggests that green space might affect health by inducing beneficial physical

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