Small Intestinal Bacterial Overgrowth and Systemic Laboratory Parameters: A Multivariable Cross-Sectional Analysis

Background: Small intestinal bacterial overgrowth (SIBO) has been linked to systemic inflammation and vitamin D deficiency, but its independent clinical relevance remains uncertain. Methods: In this cross-sectional study, 162 adults undergoing hydrogen breath testing were evaluated. Serum 25-hydroxyvitamin D [25(OH)D], leukocyte count, red blood cell distribution width—standard deviation (RDW-SD), and C-reactive protein were analyzed. Associations were assessed using unadjusted comparisons and multivariable regression models adjusted for age, sex, and BMI. Hydrogen increment was additionally examined as a continuous variable. Results: In unadjusted analyses, SIBO-positive individuals had lower 25(OH)D levels and higher leukocyte counts. However, after adjustment for age, sex, and BMI, SIBO status was not independently associated with 25(OH)D, leukocyte count, or RDW-SD. BMI was independently associated with leukocyte count, and age with RDW-SD. Hydrogen increment was not correlated with laboratory parameters. Conclusions: SIBO was not independently associated with vitamin D status or systemic hematological markers. Host-related factors, particularly BMI and age, appeared to have a greater influence on laboratory variability than SIBO.