The role of biodiversity in the development of asthma and allergic
sensitization: a systematic review and meta-analysis
Abstract
Changes in land use and climate change have been reported to reduce
biodiversity of the environment and human microbiota. This may lead to
inadequate and unbalanced stimulation of immunoregulatory circuits and
ultimately, to clinical diseases, such as asthma and allergies. We
summarised available empirical evidence on the role of inner and outer
layers of biodiversity in the development of asthma, asthma-like
symptoms, and allergic sensitization. We conducted a systematic search
in SciVerse Scopus, PubMed MEDLINE, and Web of Science up to 5 December
2022 to identify relevant studies assessing the relations between inner
and outer layers of biodiversity and the risk of asthma, wheezing and/or
allergic sensitization. We applied random-effects models to calculate
summary effect estimates. The protocol was registered in PROSPERO
(CRD42022381725). Of 75 studies, 20 provided effect estimates for the
meta-analysis showing an association between high outer layer
biodiversity and a low risk of asthma development (Shannon diversity
index: OR (95% CI) = 0.77 (0.55; 1.06); bacterial richness: OR (95%
CI) = 0.74 (0.57; 0.96)). Although the evidence on the effect of inner
layer biodiversity suggested that bacterial diversity was slightly
higher among individuals with asthma, there was no clear evidence of a
significant association between inner layer biodiversity and the risk of
asthma, wheezing or allergic sensitization. The weight of evidence
suggests that environmental exposure to high biodiversity may protect
from the development of asthma, whereas there was no consistent evidence
on any association between inner layer biodiversity and asthma, wheezing
or allergic sensitization.