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2.3 Biodiversity and Physical Health
In this section, we consider the range of connections and pathways between biodiversity and human physical health, beginning with the scale of the human body
before looking at processes operating at wider spatial scales. Given that much of the
evidence in the previous section considered the natural environment in a broad
sense, here we examine how biodiversity metrics are linked to ecosystem functions
affecting physical health.
In considering the role of biodiversity on human health it is useful to start by
recognising the human body as an ecosystem, with both internal and external microbiota, something that has been termed the human core microbiome (Karkman et al.
2017). The human gut alone contains some 1,014 bacterial strains and species as
well as other micro-organisms and viruses, the mix of which is unique to each individual and which changes during the life course (Odamaki et al. 2016; Seksik and
Landman 2015). The concept of the exposome has been developed to recognize the
role of factors shown in Fig. 2.1 in determining human health and well-being, the
significance of environment and how human health is affected by cumulative influences over time, and therefore the life course (Renz et al. 2017). Renz et al. (2017)
further propose the meta-exposome as a means of connecting human exposures with
those of the wider biosphere and linking ecosystem health at all scales to human
health (Fig. 2.3), a notion that is echoed elsewhere (e.g. Sandifer et al. 2015).
Major microbiota colonisation events are associated with particular parts of the
human life cycle, such as birth, but continue throughout the life course dependent
on lifestyle, environment and exposure (Ruokolainen et al. 2017). The so-called
‘old friends’ hypothesis also relates to this process of gaining health benefits from
beneficial symbiotic microbes. Benefits are associated with many of the body organ
systems and are multi-functional. For example, as well as helping with the healthy
development of the immune system, beneficial microbes can also perform protective roles when human hosts encounter allergens (Rook 2013; Ruokolainen et al.
2017). Both environmental and behavioural factors are involved in the development
of dysbiosis, where alterations in microbiota may result in a negative cycle of illheath (Fig. 2.3). Dysbiosis is also implicated in problems associated with the integumentary, digestive and urinary/renal systems as well as disorders in the respiratory
and cardiovascular systems (Carding et al. 2015; Renz et al. 2017). Lack of contact
with sources of symbiotic microbiota is one of the outcomes of people’s growing
‘extinction of experience’ of natural environments, and lack of contact even of itself
tends to promote greater disassociation (Cox and Gaston 2018).
Of course, biodiversity does not just affect human health through the body’s
own ecosystem. As well as affecting humans directly, such microbiota relationships also underpin the healthy functioning of wider ecosystems on which humans
depend (Flandroy et al. 2018). Biodiversity is also important at community, neighbourhood and regional scales. For example, in Australia, where 31% of the population are estimated to be affected by long-term respiratory conditions, after
socio-economic factors, the second and third most important determinants of
2 Biodiversity, Physical Health and Climate Change: A Synthesis of Recent Evidence
2.3 Biodiversity and Physical Health
In this section, we consider the range of connections and pathways between biodiversity and human physical health, beginning with the scale of the human body
before looking at processes operating at wider spatial scales. Given that much of the
evidence in the previous section considered the natural environment in a broad
sense, here we examine how biodiversity metrics are linked to ecosystem functions
affecting physical health.
In considering the role of biodiversity on human health it is useful to start by
recognising the human body as an ecosystem, with both internal and external microbiota, something that has been termed the human core microbiome (Karkman et al.
2017). The human gut alone contains some 1,014 bacterial strains and species as
well as other micro-organisms and viruses, the mix of which is unique to each individual and which changes during the life course (Odamaki et al. 2016; Seksik and
Landman 2015). The concept of the exposome has been developed to recognize the
role of factors shown in Fig. 2.1 in determining human health and well-being, the
significance of environment and how human health is affected by cumulative influences over time, and therefore the life course (Renz et al. 2017). Renz et al. (2017)
further propose the meta-exposome as a means of connecting human exposures with
those of the wider biosphere and linking ecosystem health at all scales to human
health (Fig. 2.3), a notion that is echoed elsewhere (e.g. Sandifer et al. 2015).
Major microbiota colonisation events are associated with particular parts of the
human life cycle, such as birth, but continue throughout the life course dependent
on lifestyle, environment and exposure (Ruokolainen et al. 2017). The so-called
‘old friends’ hypothesis also relates to this process of gaining health benefits from
beneficial symbiotic microbes. Benefits are associated with many of the body organ
systems and are multi-functional. For example, as well as helping with the healthy
development of the immune system, beneficial microbes can also perform protective roles when human hosts encounter allergens (Rook 2013; Ruokolainen et al.
2017). Both environmental and behavioural factors are involved in the development
of dysbiosis, where alterations in microbiota may result in a negative cycle of illheath (Fig. 2.3). Dysbiosis is also implicated in problems associated with the integumentary, digestive and urinary/renal systems as well as disorders in the respiratory
and cardiovascular systems (Carding et al. 2015; Renz et al. 2017). Lack of contact
with sources of symbiotic microbiota is one of the outcomes of people’s growing
‘extinction of experience’ of natural environments, and lack of contact even of itself
tends to promote greater disassociation (Cox and Gaston 2018).
Of course, biodiversity does not just affect human health through the body’s
own ecosystem. As well as affecting humans directly, such microbiota relationships also underpin the healthy functioning of wider ecosystems on which humans
depend (Flandroy et al. 2018). Biodiversity is also important at community, neighbourhood and regional scales. For example, in Australia, where 31% of the population are estimated to be affected by long-term respiratory conditions, after
socio-economic factors, the second and third most important determinants of
2 Biodiversity, Physical Health and Climate Change: A Synthesis of Recent Evidence