Environmental change and human health: Can environmental proxies inform the biodiversity hypothesis for protective microbial-human contact?

Microbiota from environmental sources overlap and interact with human microbiota, contribute to human microbial diversity, and provide beneficial immunomodulatory stimuli. Meanwhile, reduced diversity in human microbiota and immune dysregulation have been associated with a range of diseases. Emerging evidence suggests landscape-scale drivers of microbial diversity may influence our health, but the area remains understudied because of its multidisciplinary nature. Here, we attempt to widen the view on this subject by offering an environmental researcher's viewpoint, proposing a unifying conceptual framework to stimulate multidisciplinary interest. To focus research in this challenging area, we propose greater emphasis on multiscale ecological links and that landscape-scale proxies for potential underlying microbial mechanisms be investigated to identify key environmental attributes and health relationships worthy of subsequent detailed examination. Wherever possible, ecological epidemiological studies should account for the temporal nature of environmental microbiota exposures, especially with respect to the early development of the human commensal microbiota.