Supplemental Material for: No Independent Association Between Serum Zinc Levels and Endoscopic Disease Activity Assessed by the Ulcerative Colitis Endoscopic Index of Severity: A Single-Center Retrospective Study

This single-center retrospective observational study included consecutive serum zinc–endoscopy pairs from patients with UC. The primary analysis included serum zinc measurements obtained within 30 days of endoscopy, whereas serum zinc measurements obtained within 180 days were analyzed as a sensitivity analysis. Endoscopic activity was assessed using the total UCEIS score.

Associations were evaluated using Spearman’s correlation and multivariable linear mixed-effects models adjusted for age, sex, disease extent, serum albumin, C-reactive protein, and advanced therapy, with a random intercept for patient.</p><p dir="ltr">Results: The primary analysis included 44 serum zinc–endoscopy pairs from 40 patients. Serum zinc levels showed a weak, non-significant negative correlation with UCEIS scores in univariate analysis (Spearman's ρ = −0.23, p = 0.139).

In the primary linear mixed-effects model, serum zinc levels were not independently associated with UCEIS (β = −0.186, 95% CI −0.572 to 0.200; p = 0.335). In a sensitivity analysis excluding serum albumin from the model, serum zinc levels were significantly associated with UCEIS (β = −0.389, 95% CI −0.728 to −0.051; p = 0.028). Results from the 180-day sensitivity analysis were consistent with those of the primary analysis.</p><p dir="ltr">Conclusion: Serum zinc levels were not independently associated with endoscopic disease activity.

These findings suggest that nutritional and inflammatory status should be considered when interpreting serum zinc levels in patients with ulcerative colitis.</p>