Two-year study reveals the startling impact that playing in nature has on children's immune systems, and their likelihood of developing allergies and diseases such as asthma and diabetes. Researcher Marja Roslund talks about the dramatic changes they measured in children's ability to fight off illnesses and the reduction in harmful bacteria found in their gut, after they rewilded the children's daycare centres, bringing in soil, plants and even a section of forest floor. She also explains the causal link between the explosion in allergies and conditions such as asthma and diabetes, and the changes we can make to make a difference.

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