Assessment of 25(OH)D Levels, Their Association with Disease Activity and Nutritional Status in Inflammatory Bowel Disease: A Cross-Sectional Comparative Study

Background/Objectives: Vitamin D deficiency may increase the risk of IBD and be associated with disease activity. The aim of the study was to assess vitamin D levels, their association with disease activity in patients with IBD. Methods: A total of 231 subjects took part in the cross-sectional comparative study, including 129 patients with IBD and 102 healthy individuals Disease Activity Index and the Montreal classification were used to assess disease activity in patients with CD. For patients with UC, the Partial Mayo Score and the Montreal classification were applied. To determine total 25(OH)D chemiluminescent immunoassay (CLIA) technology was used. Results: The concentration of 25(OH)D was significantly lower in the group of patients with IBD compared to the control group (25.5 ng/mL vs. 28.8 ng/mL, p = 0.0027). Differences in 25(OH)D concentrations depended on IBD activity, with significantly higher vitamin D concentrations found in patients in remission compared to those with active IBD (28.9 ± 7.2 ng/mL vs. 22.3 ± 6.1 ng/mL, p = 0.0022). This association was confirmed for both UC and CD patients. A multivariate adaptive regression model using spline curves revealed a relationship between serum 25(OH)D concentrations in patients with IBD and total dietary vitamin D intake, including vitamin D supplementation, consumption of one serving of fish per week, and disease remission. Conclusions: Serum 25(OH)D levels in IBD patients may serve as an additional, useful, and non-invasive marker of disease activity.