Helsinki alert of biodiversity and health.

Urban living in built environments, combined with the use of processed water and food, may not provide the microbial stimulation necessary for a balanced development of immune function. Many chronic inflammatory disorders, including allergic, autoimmune, metabolic, and even some behavioural disorders, are linked to alteration in the human commensal microbiota. Sedentary lifestyle is associated with reduced exposure to a broad spectrum of environmental micro-organisms and surplus energy balance, both risk factors of chronic inflammatory disorders. According to the Biodiversity Hypothesis, an environment with diverse macrobiota and microbiota modifies and enriches the human microbiota, which in turn is crucial in the development and maintenance of appropriate immune function. These issues were discussed in the symposium 'Chronic Inflammation, Lifestyle and Environment', held in Helsinki, 20-22 August 2014, under the sponsorship of the Yrjö Jahnsson Foundation. This paper briefly outlines the recent findings in the context of the environment, lifestyle, and health; discusses the forces that undermine immune tolerance in urban environments; and highlights the possibilities to restore broken immune tolerance among urban dwellers, summarizing the main messages in four statements and calling for actions to combat major public health threats.