Photo by Loren Kerns
There are many lifestyle and environmental factors that affect our microbiota composition, and aspects of our neighborhoods have a lot to do with those factors. Researchers have found, for example, that changes in diet rapidly alter our microbiome. Diet, of course, depends on what food is available in one’s community, so someone living in an area with access to only processed foods will have a different microbial composition than someone who lives right next to a healthy food store. It is important to note that many of the factors shown to reduce gut microbial diversity, such as highly processed foods, physical inactivity, stress, heavy antibiotic use, and exposure to pollutants, are disproportionately prevalent in low socio-economic (SES) neighborhoods. A 2016 study, for example, found that as neighborhood socioeconomic-status increases, so does the diversity of the colonic and fecal microbiota. There is even evidence that the presence or absence of green space affects the bacteria to which we are exposed.
While the mechanisms through which microbiota composition can affect health are still unclear, existing research tells us that there is reason to suspect some sort of causal relationship between microbial composition and the onset and progression of certain diseases. Future research will need to evaluate this relationship and seek to further identify both the pathways that allow our microbiome to impact our health, and the environmental factors that may contribute to socioeconomic and neighborhood differences in microbial composition.
Even if a causal relationship does exist, however, some would argue that the question of “cause or consequence” is not necessarily of the greatest importance. One researcher points out that while we often ask whether changes in the gut microbiome are a cause or a consequence of disease, “a better question may be whether the altered microbiome contributes to the disease.” He goes on to suggest that “whatever the trajectory that leads to the alteration of the neglected microbial organ of our body, it needs to be treated to the best of our abilities, in order to improve the patients’ health.”
This last sentiment reflects the fundamental aim of public health—ultimately, the goal of research is to improve peoples’ lives, and future research should focus on the development and assessment of possible interventions. In order to close persistent health gaps, researchers should further investigate the mechanisms by which health disparities occur in neighborhoods.
 Gregory E. Miller, Phillip A. Engen, Patrick M. Gillevet, Maliha Shaikh, Masoumeh Sikaroodi, Christopher B. Forsyth, Ece Mutlu, Ali Keshavarzian (2015). Lower Neighborhood Socioeconomic Status Associated with Reduced Diversity of the Colonic Microbiota in Healthy Adults.
 Keisha Findley, David R. Williams, Elizabeth A. Grice, and Vence L. Bonham. Health Disparities and the Microbiome. Trends in Microbiology, (2016) 24.11(847)
 Lawrence A. David, Corinne F. Maurice, Rachel N. Carmody, David B. Gootenberg, Julie E. Button, Benjamin E. Wolfe, Alisha V. Ling, A. Sloan Devlin, Yug Varma, Michael A. Fischbach, Sudha B. Biddinger, Rachel J. Dutton & Peter J. Turnbaugh (23 January 2014). Diet rapidly and reproducibly alters the human gut microbiome. Nature vol. 505 pg. 559.
 Gwynne Mhuireach, Bart R. Johnson, Adam E. Altrichter, Joshua Ladau, James F. Meadow, Katherine S. Pollard, Jessica L. Green. Urban greenness influences airborne bacterial community composition. Science of the Total Environment 571 (2016) 680–687.
 The microbiome: stress, health and disease. Rachel D. Moloney, Lieve Desbonnet, Gerard Clarke, Timothy G. Dinan, John F. Cryan. Mamm Genome (2014) 25:49–74.
 Paul J. Kennedy, Amy B. Murphy, John F. Cryan, Paul R. Ross, Timothy G. Dinan, Catherine Stanton. Microbiome in brain function and mental health. Trends in Food Science & Technology 57 (2016) 289e301
 The human gut microbiome impacts health and disease. Stanislav Dusko Ehrlich. S.D. Ehrlich / C. R. Biologies 339 (2016) 319–323.