Summary:
Urbanisation has been linked to a higher prevalence of immune-related diseases. One proposed explanation is the biodiversity hypothesis, which suggests that reduced exposure to diverse natural environments limits contact with beneficial microbes, disrupting the body’s normal microbiota and immune function. Other factors associated with urban living—including increased pollution, processed diets, antibiotic use and high hygiene practices—can also contribute to microbial imbalance. The human microbiota develops early in life and is influenced by factors such as birth method, genetics, diet, antibiotic exposure and the surrounding environment. Research suggests that greater exposure to natural environments early in life can influence both skin and gut microbiota. This intervention study investigated whether increasing biodiversity in urban daycare environments could improve children’s microbiota and immune function. Seventy-five children aged 3-5 years attended one of three daycare settings: standard urban centres, centres where the outdoor play areas were enriched with forest floor and natural environments, or nature-oriented centres where children visited nearby forests daily. Skin and gut microbiota, blood cytokine concentrations and regulatory T cell levels were assessed before and after a 28-day intervention. This study found that children exposed to the biodiversity-enriched environments developed greater diversity of beneficial skin bacteria, increased levels of the anti-inflammatory cytokines, and a higher proportion of regulatory T cells, indicating enhanced immune regulation. The changes in children’s skin microbiota also reflected the microbial composition of the enriched outdoor environments. Although changes in gut microbiota were less pronounced than those observed on the skin, the findings suggest that increasing exposure to biodiverse natural environments may strengthen immune regulation and could represent a practical strategy for reducing the risk of immune-mediated diseases in urban populations.
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Abstract:
As the incidence of immune-mediated diseases has increased rapidly in developed societies, there is an unmet need for novel prophylactic practices to fight against these maladies. This study is the first human intervention trial in which urban environmental biodiversity was manipulated to examine its effects on the commensal microbiome and immunoregulation in children. We analyzed changes in the skin and gut microbiota and blood immune markers of children during a 28-day biodiversity intervention. Children in standard urban and nature-oriented daycare centers were analyzed for comparison. The intervention diversified both the environmental and skin Gammaproteobacterial communities, which, in turn, were associated with increases in plasma TGF-β1 levels and the proportion of regulatory T cells. The plasma IL-10:IL-17A ratio increased among intervention children during the trial. Our findings suggest that biodiversity intervention enhances immunoregulatory pathways and provide an incentive for future prophylactic approaches to reduce the risk of immune-mediated diseases in urban societies.
Article Publication Date: 14/10/2020
DOI: 10.1126/sciadv.aba2578
