COS 77-4 - A Meta-Analysis of Diversity-Disease Relationships in the Human Microbiome

Abstract: In nature, increased species diversity often leads to a lower prevalence of infectious disease. Many mechanisms have been proposed to explain such diversity-disease relationships in nature, such as transmission reduction by which the probability of a pathogen encountering a susceptible host is reduced with increased species diversity, or susceptible host regulation by which diversity acts to reduce the density of susceptible hosts. Similar mechanisms are suspected to operate in the human microbiome, which can be thought of as its own ecosystem; for example, increased microbial diversity may reduce disease because there are fewer open niches in the microbiome for pathogens to invade (much like diverse ecosystems are predicted to be more resilient to species invasions). The human microbiome has been studied extensively concerning its role in disease outcomes, however, it has not been studied as broadly from an ecological perspective. My research bridges this gap by assessing evidence for diversity-disease relationships in the human microbiome and if increased microbial diversity is associated with reduced disease in humans? If diversity-disease relationships operate similarly in the human microbiome as in nature, then I predict to observe more negative relationships than positive relationships between microbial diversity and human health outcomes.


To test this hypothesis, I performed a meta-analysis to quantitatively synthesize the relationship between microbial diversity and human health outcomes across hundreds of individual studies. Preliminary results from a random-effects meta-analysis of studies of the gastrointestinal microbiome show support for negative diversity-disease relationships in the human microbiome, with a mean estimated effect of –0.23 (95% CI: -035, -0.12) for the Shannon index, –0.13 (95% CI: -0.40, 0.15) for Chao1, and –0.18 (95% CI: -0.36, 0.01) for species richness. There was heterogeneity in the results across studies and the strength of the relationship between microbial diversity and human health outcomes varied with the type of sample collected (e.g. fecal vs mucosal), disease or condition studied (e.g. Crohn’s disease, celiac disease, psoriasis, etc.). Understanding whether and how microbial diversity affects human disease will not only help advance our understanding of diversity-disease relationships, but also have implications for human health. In addressing this question, I will advance research into the functional roles of the human microbiome for human health by integrating fundamental principles from community ecology.