Lower Neighborhood Socioeconomic Status Associated with Reduced Diversity of the Colonic Microbiota in Healthy Adults

Abstract

In the United States, there are persistent and widening socioeconomic gaps in morbidity and mortality from chronic diseases. Although most disparities research focuses on person-level socioeconomic-status, mounting evidence suggest that chronic diseases also pattern by the demographic characteristics of neighborhoods. Yet the biological mechanisms underlying these associations are poorly understood. There is increasing recognition that chronic diseases share common pathogenic features, some of which involve alterations in the composition, diversity, and functioning of the gut microbiota. This study examined whether socioeconomic-status was associated with alpha-diversity of the colonic microbiota. Forty-four healthy adults underwent un-prepped sigmoidoscopy, during which mucosal biopsies and fecal samples were collected. Subjects' zip codes were geocoded, and census data was used to form a composite indicator of neighborhood socioeconomic-status, reflecting household income, educational attainment, employment status, and home value. In unadjusted analyses, neighborhood socioeconomic-status explained 12-18 percent of the variability in alpha-diversity of colonic microbiota. The direction of these associations was positive, meaning that as neighborhood socioeconomic-status increased, so did alpha-diversity of both the colonic sigmoid mucosa and fecal microbiota. The strength of these associations persisted when models were expanded to include covariates reflecting potential demographic (age, gender, race/ethnicity) and lifestyle (adiposity, alcohol use, smoking) confounds. In these models neighborhood socioeconomic-status continued to explain 11-22 percent of the variability in diversity indicators. Further analyses suggested these patterns reflected socioeconomic variations in evenness, but not richness, of microbial communities residing in the sigmoid. We also found indications that residence in neighborhoods of higher socioeconomic-status was associated with a greater abundance of Bacteroides and a lower abundance of Prevotella, suggesting that diet potentially underlies differences in microbiota composition. These findings suggest the presence of socioeconomic variations in colonic microbiota diversity. Future research should explore whether these variations contribute to disparities in chronic disease outcomes.

Fig 1. Scatter-plot of the neighborhood SES and alpha-diversity.

Figs depict associations between neighborhood SES and alpha-diversity in biopsies excised from sigmoid mucosa (upper plots) and feces collected from sigmoid lumen (lower plots). Shannon and Chao1 indices are different metrics for calculating alpha-diversity.

Fig 2. Map depicting the neighborhood SES and alpha-diversity.

Map of greater Chicago region, illustrating associations between neighborhood SES and alpha-diversity in biopsies excised from sigmoid mucosa. Depicted are neighborhood SES (left panel), and two metrics of diversity, the Shannon (middle panel) and Chao1 (right panel) indices. For each variable, the sample was divided into quartiles, and neighborhoods were colored as follows: Red = lower 25% of sample; Yellow = 26–50%; Green = 51–75%; Blue = upper 25%. Geospatial data sources: Urban place area from TIGER/Line US Census 2010; Illinois and Wisconsin zip codes from TIGER/Line US Census 2010; Water area from TIGER/Line US Census 2010; Interstate lines from TIGER/Line US Census 2010.

Fig 3. Scatter-plot of neighborhood SES and bacterial genera.

Figs depict associations between neighborhood SES and Prevotella to Bacteroides ratio (upper panel), as well as relative abundance of Prevotella (middle panel) and Bacteroides (lower panel). Specimens are biopsies excised from sigmoid mucosa.