Page - 25 - in Biodiversity and Health in the Face of Climate Change

25 2.3 Biodiversity and  Physical Health In this section, we consider the range of connections and pathways between biodi- versity 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 micro- biota, 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 indi- vidual 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 influ- ences 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 protec- tive 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 ill- heath (Fig.  2.3). Dysbiosis is also implicated in problems associated with the integ- umentary, 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 relation- ships also underpin the healthy functioning of wider ecosystems on which humans depend (Flandroy et  al. 2018). Biodiversity is also important at community, neigh- bourhood and regional scales. For example, in Australia, where 31% of the popula- tion 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