Gut Microbiome Composition in Older Adults with PTSD Symptoms and Trauma-Exposed Controls: Findings from the GUMP Study

Background: Emerging evidence suggests that alterations in the gut microbiome may contribute to mental health outcomes through the gut-brain axis. However, older adults with post-traumatic stress disorder (PTSD) remain underrepresented in microbiome research. This pilot study investigated associations between PTSD symptoms, dietary fibre intake, cognitive function, and gut microbiome functional capacity in adults aged 50 years and older. Methods: Participants with PTSD symptoms and trauma-exposed controls (TEC) completed validated assessments of mental health, trauma exposure, and dietary fibre intake. A subset of participants provided stool samples for microbiome analysis and undertook cognitive function assessment. Quantitative PCR was used to assess phylum-level taxonomy and butyrate-producing bacterial pathways (terminal butyrate generating enzyme), with abundances normalised to the 16S rRNA gene. Results: Participants with PTSD demonstrated significantly greater mental health symptom burden and poorer performance on cognitive tasks related to executive function, working memory, and learning. Dietary fibre intake did not differ significantly between PTSD and TEC groups and no significant differences in overall microbial composition were identified at the phylum level. In contrast, differences were more apparent when assessing functional microbiome pathways, with butyrate kinase abundance significantly lower in PTSD participants than TEC participants. When stratified by fibre intake, a greater butyrogenic capacity was observed in the High fibre TEC participants compared to the Low fibre TEC participants, while little difference was observed in the PTSD fibre-stratified groups. Substantial inter-individual variation was also evident across both taxonomic and functional measures. Conclusions: These findings suggest that functional characteristics of the gut microbiome may provide greater insight into PTSD-related biological processes than broad taxonomic measures alone. Dietary fibre intake may be associated with greater butyrate-producing capacity in trauma-exposed older adults without PTSD symptoms, although this relationship appeared less evident among older adults living with PTSD symptoms. These findings support further investigation of microbiome function, diet, and cognition within the gut-brain axis. Larger studies incorporating metagenomic and metabolomic approaches are warranted.