Seasonal 25-hydroxyvitamin D levels in new childhood-onset SLE: associations with disease activity and peripheral lymphocyte subsets

Objective This study aimed to compare 25-hydroxyvitamin D (25-(OH)D) levels and peripheral lymphocyte subsets between children with new childhood-onset SLE and healthy controls across different seasons, and to explore the relationships of seasonal 25-(OH)D concentrations with the disease activity and peripheral lymphocyte subsets in paediatric patients with SLE. Methods A retrospective study was conducted, enrolling 285 patients with new childhood-onset SLE and 175 healthy children. All participants were divided into a winter-spring group and a summer-autumn group according to sampling seasons. Serum 25-(OH)D levels and peripheral lymphocyte subsets were detected and quantified. Results Compared with healthy controls, patients with SLE presented with significantly higher proportions of CD8 + T cells (p<0.05), alongside lower total lymphocyte counts, lower percentages of CD4 + T cells and Natural Killer(NK) cells, reduced CD4 + /CD8 + ratio and decreased serum 25(OH)-D levels (all p<0.05). Within the SLE cohort, patients in the summer-autumn SLE group had markedly higher serum level of 25-(OH)D levels than those in the winter-spring group (18.1 vs 22.8 ng/mL; p<0.001). 25-(OH) D deficiency was correlated with a higher prevalence of lupus nephritis, higher Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) scores and lower serum calcium levels. In both seasonal subgroups, serum calcium and serum albumin showed weak positive correlations with serum 25-(OH)D levels. A moderate negative correlation was observed between SLEDAI-2K scores and 25-(OH)D levels in the winter-spring group, while only a weak negative correlation was detected in the summer-autumn group. Conclusions Serum 25-(OH)D levels are affected by seasonal changes and closely correlated with disease activity in children with SLE. Patients with new childhood-onset SLE manifest abnormal peripheral lymphocyte subsets and insufficient 25-(OH)D.