MDD patients with suicidal ideation showed preliminary characteristics in gut microbiota diversity, composition, and plasma levels of CRP and SCFAs, and CRP may play a partial mediating role in the relationship between Blautia and suicidal ideation, though these findings were confounded by depression severity.
MDD patients had significantly lower levels of short-chain fatty acids and higher CRP levels compared to healthy controls.
Alpha diversity was significantly lower in MDD patients with suicidal ideation compared to healthy controls, and also lower than MDD patients without suicidal ideation.
Beta diversity analysis showed significant differences in gut microbiota composition among the three groups (HC, SC0, SC1).
Linear discriminant analysis effect size (LEfSe) identified 24 differentially abundant bacterial taxa across classification levels among the three groups.
Blautia abundance was positively correlated with suicidal ideation severity, depression severity, and CRP levels, while Bacteroides, Roseburia, and Sutterella were negatively correlated with suicidal ideation and depression severity.
CRP may partially mediate the relationship between Blautia abundance and suicidal ideation intensity, but this mediating effect was confounded by depression severity.
This research suggests that people with major depressive disorder (MDD) who also experience suicidal thoughts have distinct patterns in their gut bacteria compared to both people with MDD who do not have suicidal thoughts and healthy individuals. Specifically, those with suicidal ideation showed less diversity in their gut microbiome, lower levels of beneficial short-chain fatty acids (like acetic, propionic, and butyric acids), and higher blood levels of C-reactive protein (CRP), a marker of inflammation. Certain bacterial groups—particularly Blautia—were more abundant and linked to greater suicidal ideation and depression severity, while others like Bacteroides, Roseburia, and Sutterella were less abundant and inversely associated with these symptoms. The study also found preliminary evidence that inflammation, as measured by CRP, may act as a partial link between the gut bacterium Blautia and the severity of suicidal thoughts, though this relationship was intertwined with how severe a person's depression was overall. This makes it difficult to determine whether the gut microbiota changes are specifically related to suicidal ideation or are more broadly a feature of depression severity. This research suggests that the gut-brain connection—sometimes called the gut-brain axis—may be relevant to understanding suicidal ideation in MDD, potentially through inflammatory pathways. However, the authors caution that the findings are exploratory and confounded by depression severity, meaning further research with larger samples and more controlled study designs is needed before any clinical conclusions can be drawn.
Li F, Jiang Z, Xing J, Guo F, Qu C, Zhang A, et al.. (2026). Characterization and correlation of gut microbiota in major depressive disorder patients with suicidal ideation.. BMC psychiatry. https://doi.org/10.1186/s12888-026-08290-9