Abstract / Summary
Climate change and urbanization are associated with reduced greenness and vegetation diversity, depletion of biodiversity, and impoverishment of human microbiota. These changes may influence immune regulation and increase the risk of many chronic inflammatory diseases, such as asthma. This study presents the results of a meta-analysis of the association between exposure to environmental and human microbiota biodiversity and the development of asthma. The effect estimates for biodiversity were summarized as the standardized mean difference or relative risk with 95% confidence interval applying the Hedges method and the restricted maximum likelihood estimator, respectively. The summary effect estimates for the association between environmental biodiversity, using the Shannon index, and asthma was not statistically significant; whereas higher bacterial richness showed a significant protective association with asthma, although the considerable heterogeneity across the studies and publication bias. For human microbiota diversity, the summary standardized mean difference suggested that the risk of asthma was associated with high bacterial diversity and bacterial richness/abundance, while the OR‑based estimate for bacterial richness and asthma was not significant. Our meta-analysis shows variable associations between exposure to environmental and human microbiota biodiversity and asthma, with the direction and magnitude of these associations depending on the specific biodiversity metrics and analytical approaches used. Biodiversity loss is associated with several adverse health effects. Here, the authors report the results of a meta-analysis investigating the effect of exposure to high environmental and human biodiversity on the risk of asthma.