four clinical examinations over a 15-year period of 6076 individuals, aged 45–69
years at baseline, who participated in the Whitehall II study revealed a 13% lower
risk of metabolic syndrome in people living within 500 m of green space (de Keijzer
et al. 2019). Such longitudinal data reinforce the classical study of approximately
40 Â 10
6 UK citizens which suggested that living in proximity to green space
reduced the risk of cardiovascular disease and prolonged overall survival (Mitchell
and Popham 2008).
18.2.2 Psychiatric Disorders
Psychiatric disorders constitute another major group. A study of approximately
1 million Danish citizens found that living close to high levels of green space during
childhood reduced the risk of most mental illnesses later in life. In contrast, for those
most deprived of green space during childhood, the risk of mental illness was up to
55% higher (Engemann et al. 2019), and similar results for depression and anxiety
were reported in a large study in the Netherlands (Maas et al. 2009). Clearly, there
are many possible explanations for this relationship, but evidence suggesting a role
for the microbiota of the natural environment is described later.
18.2.3 Allergies
In the late nineteenth century, it was noted that farmers were less likely to develop
hay fever than were city dwellers (Blackley 1873). Since then hundreds of epidemiological studies have confirmed that exposure to the farming environment in early
life diminishes the risk of allergic disorders (Ege et al. 2011; Stein et al. 2016), while
other studies have shown that merely living in proximity to green spaces lowers the
risk of allergic sensitisation (Hanski et al. 2012). Importantly, some of these papers
include immunological findings that strongly indicate cause and effect, rather than
merely chance association (Hanski et al. 2012; Stein et al. 2016). These mechanistic
points will be discussed later.
18.3 What Organisms from the Natural Environment Do
We Meet?
In the past, we encountered organisms from the natural environment in our homes.
The homes of our evolving ancestors were caves or shelters that were part of the
natural environment, or constructed with timber, leaves, and mud taken from that
environment. Even more recently, mediaeval homes were built with natural timber,
334
G. A. W. Rook
years at baseline, who participated in the Whitehall II study revealed a 13% lower
risk of metabolic syndrome in people living within 500 m of green space (de Keijzer
et al. 2019). Such longitudinal data reinforce the classical study of approximately
40 Â 10
6 UK citizens which suggested that living in proximity to green space
reduced the risk of cardiovascular disease and prolonged overall survival (Mitchell
and Popham 2008).
18.2.2 Psychiatric Disorders
Psychiatric disorders constitute another major group. A study of approximately
1 million Danish citizens found that living close to high levels of green space during
childhood reduced the risk of most mental illnesses later in life. In contrast, for those
most deprived of green space during childhood, the risk of mental illness was up to
55% higher (Engemann et al. 2019), and similar results for depression and anxiety
were reported in a large study in the Netherlands (Maas et al. 2009). Clearly, there
are many possible explanations for this relationship, but evidence suggesting a role
for the microbiota of the natural environment is described later.
18.2.3 Allergies
In the late nineteenth century, it was noted that farmers were less likely to develop
hay fever than were city dwellers (Blackley 1873). Since then hundreds of epidemiological studies have confirmed that exposure to the farming environment in early
life diminishes the risk of allergic disorders (Ege et al. 2011; Stein et al. 2016), while
other studies have shown that merely living in proximity to green spaces lowers the
risk of allergic sensitisation (Hanski et al. 2012). Importantly, some of these papers
include immunological findings that strongly indicate cause and effect, rather than
merely chance association (Hanski et al. 2012; Stein et al. 2016). These mechanistic
points will be discussed later.
18.3 What Organisms from the Natural Environment Do
We Meet?
In the past, we encountered organisms from the natural environment in our homes.
The homes of our evolving ancestors were caves or shelters that were part of the
natural environment, or constructed with timber, leaves, and mud taken from that
environment. Even more recently, mediaeval homes were built with natural timber,
334
G. A. W. Rook