Supplementary Material for: Distinct Association of Serum Vitamin D Concentration with Disease Activity and Trough Levels of Infliximab and Adalimumab during Inflammatory Bowel Disease Treatment

Background: Studies of serum vitamin D (Vit-D) levels in patients with inflammatory bowel disease (IBD) treated with anti-tumor necrosis factor-alpha (anti-TNF-α) agents are scarce. The conjunction of Vit-D as well as zinc levels and anti-TNF-α-trough concentrations (TC) has not yet been explored. Objectives: To determine the association of serum Vit-D, zinc and C-reactive protein (CRP) levels with clinical and biochemical remission and a possible correlation with serum TC and antibody levels of anti-TNF-α. Methods: Serum Vit-D and zinc levels as well as Infliximab (IFX) and Adalimumab (ADA) TC during the maintenance phase of treatment were measured in 112 IBD patients. Statistical analysis were performed for clinical and biochemical remission. Results: Vit-D and zinc deficiency were detected in 58 and 4.5% of the patients respectively. In IFX-treated patients, IFX-TC, Vit-D and CRP levels were associated independently with clinical remission with an OR of 20 (95% CI 1.3–333, p = 0.03), 1.3 (95% CI 1.1–1.7, p = 0.02) and 0.4 (95% CI 0.2–0.8, p = 0.01) respectively. Serum IFX-TC and Vit-D levels correlated positively (r = 0.39, p = 0.001), while serum IFX-TC and CRP levels showed an inverse correlation (r = –0.43, p < 0.001). Only ­IFX-TC associated independently with biochemical remission with a threshold of 3.1 µg/mL. In ADA-treated patients, ADA-TC associated independently with clinical and biochemical remission with an OR of 2.5 (95% CI 1.1–5.0, p = 0.04) and 1.3 (95% CI 1.1–1.4, p = 0.03) respectively. The serum zinc level was associated neither with clinical nor with biochemical remission in either cohort. Conclusions: Our results indicate that serum Vit-D level may be a predictive marker in addition to drug trough levels in IBD patients treated with IFX. Furthermore, due to the correlation between serum IFX and Vit-D levels, Vit-D substitution should be conducted in patients with low Vit-D levels.