Increased number of children in households may protect against inflammatory bowel disease.

BACKGROUND: The increasing incidence of inflammatory bowel disease (IBD: Crohn's disease and ulcerative colitis) around the world has coincided with a wide array of environmental and epidemiologic changes. The relationship between IBD incidence and household or family size decline, however, has not been examined before. Our background epidemiological analyses suggested an inverse association between household size and IBD incidence. We aimed to examine this further in a murine model. METHODS: We designed a unique two-generation cohousing model of family size and IBD susceptibility in C57BL/6J mice. Serial fecal microbiomes during cohousing were examined by high-throughput 16S rRNA sequencing. After cohousing for 10 days, mice were exposed to dextran sulfate sodium (DSS) to induce acute colitis. Body weight as a significant correlate of colitis severity was measured. RESULTS: Mice in a large household arrangement demonstrated less weight loss than mice in the small household arrangement in the DSS model. Age- and housing-dependent microbiome shifts were found. CONCLUSIONS: Larger households may be protective against intestinal inflammation through intergenerational microbiome modulation. Our observations may set the foundation for age-dependent, microbiome-directed future prevention against IBD. IMPACT: Epidemiological analyses in this study suggested that IBD incidence may inversely correlate with household size (an indicator of family size/children per family), which has not been examined before. A uniquely designed two-generation cohousing model of family size and IBD susceptibility in mice supported our epidemiologic observations. Microbiome changes in our cohousing model may set the foundation for age-dependent, microbiome-directed prevention against IBD.