Chronic vascular complications remain a major clinical burden in individuals with long-standing type 1 diabetes mellitus (T1DM). In Cardiovascular Diabetology, a cross-sectional analysis examined associations between oral and gut microbiome features and vascular complications in T1DM.

The study enrolled 75 participants with T1DM of at least 10 years’ duration and 43 healthy controls. All participants underwent comprehensive clinical assessment. This included blood glucose testing, lipid profiling, and complication-related examinations. Fecal and oral rinse samples were collected. Shotgun metagenomic sequencing was performed. Participants with T1D were stratified by the presence of microvascular complications, macrovascular complications, or no complications. Microbial composition was compared across groups.

Significant differences in oral and gut microbiota were observed between T1DM participants with and without vascular complications. A core set of 26 gut microbial species and 8 oral microbial species was specifically associated with complications. Butyrate-producing gut bacteria, including Blautia wexlerae, Anaerobutyricum hallii, Roseburia inulinivorans, and Anaerobutyricum soehngenii, were enriched in individuals without complications. Specific oral Neisseria species showed similar enrichment. Mediation analyses showed associations consistent with partial mediation between selected microbial species and relationships of glycemic control or insulin resistance with complication risk. These measures included glycated hemoglobin (HbA1c), glucose risk index, and estimated glucose disposal rate. Classification models integrating both oral and gut microbial features outperformed models based on either site alone in distinguishing T1DM participants with complications.

These findings link distinct oral and gut microbiome features with chronic vascular complications in long-standing T1DM.