Shared and condition-associated gut microbiota alterations in older adults with depression and constipation: evidence from the American Gut Project.

Background: Constipation and depression frequently co-occur in older adults, and growing evidence suggests that gut microbiota dysbiosis may be a shared feature of both conditions. The microbiota has well-established roles in gastrointestinal motility and gut-brain axis signaling, and compositional alterations have been independently reported in each condition. However, whether older adults with constipation and those with depression share common microbiota characteristics have not been systematically investigated. Aim: This study aimed to characterize gut microbiota alterations in older adults with depression or constipation using 16S rRNA amplicon sequencing data from the American Gut Project, focusing on microbial features shared by, or specific to, the two conditions. Methods: We retrieved fecal 16S rRNA sequencing data from 513 older adults in the publicly available American Gut Project database, including HC ( Results: Alpha diversity was comparable among groups, whereas beta diversity revealed detectable differences in community composition. After adjustment for age, sex, and BMI, Bray-Curtis-based differences remained evident, with the most consistent pairwise difference between CP and HC. At the genus level, CP showed depletion of health-associated butyrate-producing taxa and enrichment of selected mucin- or inflammation-associated taxa, whereas DP was characterized by enrichment of Erysipelatoclostridium and [Ruminococcus]_gnavus_group and depletion of UCG-002 and selected health-associated genera. Random forest analyses further identified key microbial contributors to group discrimination. Conclusion: We identified subtle and partially overlapping genus-level microbiota alterations in older adults with constipation and depression, with constipation showing the most consistent differences from healthy controls. These findings provide exploratory evidence that selected microbiota alterations may be relevant to the clinical overlap between the two conditions, although their functional roles require validation in longitudinal studies integrating metagenomic and metabolomic profiling.