Page - 21 - in Biodiversity and Health in the Face of Climate Change

21 2.2 Nature’s Contributions to  Physical Health In this section, we consider how ecosystems influence human physical health. We discuss direct and indirect pathways which connect the natural environment to human physical health with a particular emphasis on ecosystem regulatory func- tions (e.g. modification of environmental stressors) and provisioning functions (such as the use of ecosystems by people for food, fresh water and fuel). For exam- ple, direct pathways include the health benefits from the consumption of nutritious food and indirect pathways include health benefits due to increased physical activity rates associated with the natural environment. In making this distinction, it is impor- tant to note that beyond the more obvious examples given above, the type and form of pathways are not always fully clear.  Whether a process is considered direct or indirect may differ depending on the primary consideration in hand, be it human biological systems, physical environmental systems or some specific  form of expo- sure. We consider the evidence from the perspective of the commonly recognised body organ systems, each of which provides a particular function for physical health. The identified body systems are then referenced in subsequent sections of the chapter. The body has 11 interlinked systems: reproductive, integumentary (skin/hair), skeletal, muscular, nervous (brain/brain activity), circulatory/cardiovascular (blood/ transport of nutrients), endocrine (glands/hormones), lymphatic (associated with immune functions), digestive (food), respiratory (breathing) and urinary/renal (waste). Numerous physiological parameters associated with these systems can be measured to determine physical health. In turn, each parameter can be assessed in order to establish underlying mechanisms for the influence of nature, whether through evidenced processes or through ones that are currently only hypothetical. Psychological parameters have been the focus of much of the existing body of research on exposure to nature and the connection between nature and human health. Associated study outcomes have tended to identify positive links between nature and health (Keniger et  al. 2013). However, the range of health benefits is much wider, including in terms of cognitive function, social interaction and improved resilience (Sandifer et  al. 2015). Sandifer et  al. (2015) identify no fewer than 27 published examples of the physi- ological health benefits of interaction with nature (broadly defined as living things and associated landscapes in a wide variety of settings). While some are very broad indicators, others refer to specific physiological metrics, including reduced sympa- thetic/parasympathetic nerve activity, faster healing after illness, surgery or trauma and positive influences on diabetes. Nevertheless, some reviews point to a more inconsistent picture for specific physiological outcomes. For example, positive out- comes are shown for circulatory/cardiovascular, endocrine and immune systems but with a good deal of mixed evidence (Haluza et  al. 2014). Figure  2.2 considers evi- dence from the perspective of different pathways, but also highlights inconsisten- cies in the evidence base. 2 Biodiversity, Physical Health and  Climate Change: A  Synthesis of  Recent Evidence