Associations of vitamin status and T-lymphocyte subsets with tic severity in children: a cross-sectional study using the Yale Global Tic Severity Scale

Vitamin D insufficiency and immune dysregulation have been implicated in tic disorders; however, the relationship between vitamin status, peripheral T-lymphocyte subsets, and tic severity in children remains incompletely defined.

We aimed to evaluate associations between serum vitamin indices, peripheral lymphocyte subsets, and tic severity, measured by the Yale Global Tic Severity Scale (YGTSS) global severity score, in newly diagnosed children with tic disorders.

This single-center cross-sectional study included children aged <14 years with newly diagnosed, treatment-naive tic disorders who attended Zhangjiagang Hospital affiliated to Soochow University/The First People's Hospital of Zhangjiagang City between January 2022 and August 2025. The YGTSS global severity score was calculated as the sum of the total tic score and impairment score. Normality was assessed using the Shapiro-Wilk test. Associations were examined using Spearman correlation with Benjamini-Hochberg FDR correction and adjusted linear regression with HC3 robust standard errors. Vitamin D groups were compared using the Kruskal-Wallis test followed by Dunn-Bonferroni pairwise tests. Analyses were performed using IBM SPSS Statistics version 27.0 and R version 4.4.2.

In total, 41 children were included (29 male and 12 female participants; mean age, 8.61 ± 2.70 years). The mean YGTSS global severity score was 30.71 ± 10.25. CD4⁺ T-cell absolute count showed the strongest inverse correlation with the YGTSS global severity score (Spearman ρ = -0.474, P = 0.0017; FDR-adjusted P = 0.0260). After adjustment for age, sex, and disease duration, the association remained significant using HC3 robust standard errors (B = -0.018, 95% CI -0.031 to -0.005; P = 0.0069). The overall difference among vitamin D groups was significant (Kruskal-Wallis P = 0.0073); Dunn-Bonferroni testing identified a difference only between the <20- and 20- to <30-ng/mL groups (adjusted P = 0.0077).

Lower peripheral CD4⁺ T-cell absolute count remained associated with greater tic-related symptom burden after covariate adjustment in children with tic disorders. Vitamin D findings were exploratory, did not show a monotonic dose-response pattern, and were less robust than the CD4⁺ T-cell association. Larger prospective studies are needed.