Background: Changes in land use and climate change have profound impacts on environmental biodiversity, contributing to a lower diversity and composition of human microbiota, leading to inadequate and unbalanced stimulation of immunoregulatory circuits and ultimately to clinical disease, such as asthma and allergies. We summarized the empirical evidence on the role of biodiversity in the development of asthma, wheezing, and allergic sensitization.

Methods: We conducted a systematic search in SciVerse Scopus, PubMed MEDLINE, and Web of Science up to 5 December 2022 for relevant studies assessing the relations between inner and outer layers of biodiversity and the risk of asthma, wheezing and allergic sensitization. We performed random-effects models to calculate summary-effect estimates. The study protocol was registered in PROSPERO (CRD42022381725). 

Results: A total of 75 studies were included in the systematic review, and 20 provided effect-estimates for the meta-analyses. The results suggest an association between high outer layer (environmental) biodiversity and a low risk of the development of asthma. Although the results of the meta-analysis on the effect of inner layer (human microbiota) biodiversity suggested that bacterial diversity was slightly higher among individuals with asthma, there was no clear evidence of association between inner layer biodiversity and the risk of asthma, wheezing, and allergic sensitization.

Conclusions: Exposure to high environmental biodiversity may protect from the development of asthma, whereas there was no clear evidence of an association between inner layer biodiversity and asthma, wheezing and allergic sensitization.