Reduced gut microbiome alpha diversity associates with depressive symptom severity and somatic symptom burden in major depression

OBJECTIVE: Alteration in gut microbiome have been increasingly linked to many psychiatric disorders inclusive depression. However, findings regarding microbiome diversity in depression remain inconsistent. Differences in depression subtypes, particularly the somatic versus affective symptoms profiles may partly explain this heterogeneity in previous results. METHODS: This cross-sectional study included 31 Participants diagnosed with major depressive disorder. The participants divided into two groups by severity of depression (BDI-II >34 vs. <34) and severity of somatic symptoms of depression (somatic dimension vs. cognitive-affective dimension of BDI-II). Fecal samples were collected, and 16S rRNA gene sequencing of the V3/V4 region was performed on an Illumina platform to profile the gut microbiome. Amplicon Sequence Variants (ASVs) were used to analyze microbial alpha diversity, including ACE, Chao1 and Shannon. RESULTS: Participants with higher depressive severity showed significantly reduced gut microbiome alpha diversity compared to lower depressive state (ACE; p = 0.019, Chao1; p = 0.019, and Shannon; p = 0.053). Across the total sample, BDI-II total score correlated negatively with alpha diversity significantly for ACE (r = -0.435, p = 0.015), Chao1 (r = -0.435, p = 0.015) and Shannon (r = -0.376, p = 0.037). While the somatic dimension of the BDI-II showed significant negative correlation with all tested alpha diversity indices, no significant correlations were detected between gut microbiome alpha diversity and the cognitive-affective dimension. Shannon diversity further correlated negatively with HDRS-17 scores (p = 0.033). CONCLUSION: In conclusion, the results show that a lower diversity of gut microbiota alpha is linked to more severe depressive symptoms, specifically the somatic aspect of depression. These results emphasize the importance of considering somatic symptom profiles in microbiome research and point to the gut-brain axis as a potential target for future therapeutic interventions.