Does biodiversity improve mental health in urban settings?

BACKGROUND: Globally, the human and economic burdens of mental illness are increasing. As the prevalence and costs associated with mental illness rise, we are progressively more aware that environmental issues such as climate change and biodiversity loss impact on human health. HYPOTHESIS: This paper hypothesises that increased biodiversity in urban environments is associated with improved mental health and wellbeing. It proposes the ecological mechanism through which the association may exist, and explores the extant literature to determine the extent of empirical evidence to support our hypothesis. EVIDENCE: While there is a substantial literature investigating the impact of 'green space' and contact with nature on mental health, we identified only one original research paper that directly investigated the link between biodiversity and mental health. This suggests that the extant evidence considers only 'one part of the story', providing an evidence base which is inadequate to inform policy on biodiversity conservation and public health. IMPLICATIONS: Our hypothesised relationship between environmental change and mental health proposes conservation and restoration of biodiversity in urban environments as a form of intervention for improving human health. It also highlights the need for a better evidence base to demonstrate the synergistic benefits of increased biodiversity and mental health to decision makers. Well-designed quantitative epidemiological research is needed to establish the strength of any such causal relationship.