Effects of 1-day outpatient nutrition intervention on insulin resistance and maternal-infant outcomes in women with gestational diabetes mellitus: a single-center retrospective cohort study.

The gut microbiota-immune-brain axis is increasingly recognized as a central pathway in the pathogenesis of inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, characterized by chronic intestinal inflammation.[] Exposure to natural environments has been associated with modulation of this axis, with residential greenness associated with greater microbial diversity, reduced immune activation, and enhanced immune tolerance.[] Consistent with these mechanisms, several observational studies have reported lower incidences of IBD among individuals living in greener areas, potentially through reductions in systemic inflammation and improvements in gut microbiome composition.[] Meanwhile, COVID-19 has been associated with increased IBD risk as a possible postinfectious complication.[] This association is biologically plausible, given that SARS-CoV-2 infection provokes immune dysregulation through excess inflammatory cytokine release and increased T-helper 17 activity, pathways that are central to IBD pathogenesis.[] We therefore hypothesized that while COVID-19 may increase susceptibility to IBD, exposure to residential greenness could counteract this risk through anti-inflammatory and microbiome-supporting mechanisms. However, the extent to which residential greenness influences IBD risk in the context of COVID-19 remains poorly understood.[] To address this gap, we conducted a nationwide, population-based cohort study in South Korea using linked administrative and clinical data from the National Health Insurance Service (NHIS) of Korea, COVID-19-related data from the Korea Disease Control and Prevention Agency (KDCA), and satellite-derived greenness data based on residential GPS coordinates. We evaluated whether residential greenness, measured using the normalized difference vegetation index (NDVI), was associated with incident IBD following COVID-19, including subtype analyses for ulcerative colitis and Crohn’s disease, and stratified analyses by age, sex, comorbidity status, physical activity, and income level.