Page - 261 - in Biodiversity and Health in the Face of Climate Change

261 suggesting that if such links were important then biodiversity may increase disease. Conversely, Keesing et  al. (2010) found that, although areas of high biodiversity can be a source pool for new pathogens, there was increasing evidence that biodiversity loss can increase disease transmission. They suggested that preserving areas with endemic biodiversity should generally reduce infectious disease prevalence. Sandifer et  al. (2015) examined the links between microbial biodiversity, allergic reactions and respiratory diseases, arguing that exposure to microbial diversity can improve health, for example, reducing allergens that may also influence the man- agement of some respiratory conditions. This reinforces aspects of the ‘hygiene hypothesis’, which proposes that exposure to microbes at an early age can enhance inflammatory responses and thus heighten human resilience to allergens (Hanski et  al. 2012). This point was also reported by Ege et  al. (2011), who identified that children raised on a farm were less likely to suffer from asthma. See Damialis et  al. Chap. 3, this volume, for further discussion on allergenic responses, and  Müller et  al. Chap. 4, this volume, for more  information about vector borne disease. 11.2.8 Physical Health  – Non-Communicable Disease  Systematic review-level evidence demonstrates that proximity to greenspace is linked to a reduction in mortality due to all causes (van den Berg et  al. 2015). Cross- sectional studies show increased neighbourhood greenspace is linked to lower levels of type 2 diabetes (Bodicoat et  al. 2014). When specifically considering the role of biodiversity, the effects on physical health outcomes are likely to be indirect, via nutrition, protec- tion from stressors, positive effects on personal and socio-cultural well-being, and creation of desirable natural areas for healthy behaviour. Epidemiological studies have been useful in providing evidence of a link between exposure to greenspace and health outcomes measurable at an area and population level (Mitchell and Popham 2008; de Vries et  al. 2003). However, fully making the case for the health benefits of biodiverse environments will require further work on the type and nature of the greenspace and its links to health. Much work at the area level has tended to use crude measures of exposure to biodiversity; for example, the percentage of greenspace in the local environment. Recently, Dennis et  al. (2018) have developed a sophisticated land- cover model that incorporates socio- demographics for an urban city area. Early find- ings suggest that the strength of the health–greenspace relationship depends on the nature of the greenspace, with lower diversity greenscapes (recreational grassland) having a less strong relationship with good health compared to areas with more com- plex greenspace (e.g. shrubs and trees). Access to greenspace in general has been suggested to be beneficial in the manage- ment of long-term conditions such as obesity, cardiovascular disease and diabetes. Moreover, when people exercise in the natural environment, the impact of the two protective factors, exercise and greenspace, acting together may be greater than sim- ply summing the positive effects (i.e. may be synergistic: Shanahan et  al. 2016). The protective effect of greenspace begins early in life: among children, those with access to gardens and greenspace were less likely to be obese at age 7  years (Schalkwijk et  al. 11 Biodiversity and  Health in  the  Face of  Climate Change: Implications for  Public…