Serum 25-hydroxyvitamin D levels in pediatric atopic dermatitis: seasonal variability and association with disease...

Vitamin D has important immunomodulatory and skin barrier-protective effects that may influence the pathogenesis of atopic dermatitis (AD). However, the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and AD severity remains controversial. This study aimed to evaluate the association between serum 25(OH)D levels and disease severity assessed by the SCORAD index in pediatric patients with AD and to examine seasonal variability in vitamin D levels. In this retrospective study, pediatric patients diagnosed with AD according to the Hanifin and Rajka criteria were included, and their medical records were reviewed. Serum 25(OH)D levels measured at the time of diagnosis and disease severity assessed using the SCORAD index were recorded. Ordinal logistic regression was performed as the primary analysis to evaluate the association between serum 25(OH)D levels and AD severity across all three severity categories (mild, moderate, severe), adjusting for age, sex, food allergy, and season. As a secondary, clinically oriented analysis, disease severity was dichotomized as mild versus moderate-to-severe, and binary logistic regression together with receiver operating characteristic (ROC) curve analysis was performed to determine an optimal serum 25(OH)D cutoff value for discriminating mild disease. As a sensitivity analysis, a 25(OH)D-by-season interaction was tested within the primary ordinal model. A total of 222 pediatric patients with AD, aged 3 months to 17 years, were included. Based on SCORAD classification, disease severity was mild in 134 patients (60.4%), moderate in 62 (27.9%), and severe in 26 (11.7%). The median serum 25(OH)D level was 19.17 ng/mL (IQR 15.62-27.20). 25(OH)D levels differed significantly across SCORAD severity groups (p < 0.001), with the lowest levels observed in patients with severe disease (median 15.40 ng/mL, IQR 13.42-17.00) and the highest in those with mild disease (median 22.88 ng/mL, IQR 17.60-32.02 ng/mL). Ordinal logistic regression demonstrated that higher serum 25(OH)D levels were independently associated with lower odds of a more severe category (OR = 0.91 per 1 ng/mL increase; 95% CI 0.88-0.94; p < 0.001); food allergy was associated with higher odds of more severe disease (OR = 2.11, 95% CI 1.10-4.05, p = 0.026), and the association between 25(OH)D and severity did not differ significantly across seasons (25(OH)D-by-season interaction, p = 0.74). As a secondary, clinically oriented analysis, binary logistic regression confirmed that higher serum 25(OH)D levels were independently associated with mild AD (OR = 1.095 per 1 ng/mL increase; 95% CI 1.055-1.137; p < 0.001), and ROC analysis identified a cutoff value of 20 ng/mL for discriminating mild disease (AUC = 0.728; sensitivity = 62.7%; specificity = 84.1%). Serum 25(OH)D levels decreased significantly with increasing age (r =  - 0.233, p < 0.001), while disease severity was not significantly associated with season.

Lower serum 25(OH)D levels were significantly associated with increased disease severity in pediatric AD. Serum 25(OH)D levels below 20 ng/mL were associated with a higher likelihood of more severe disease. Although serum 25(OH)D levels varied by season, disease severity was not associated with seasonal variation. These findings support an association between vitamin D status and the clinical expression of AD; given the retrospective design, causality cannot be established, and prospective studies are needed to clarify the clinical relevance of monitoring vitamin D status in pediatric AD management.

• Vitamin D deficiency is common in children with atopic dermatitis and has been associated with increased disease severity in several studies. • The relationship between serum 25(OH)D levels and AD severity remains inconsistent across geographic regions and patient populations.

• In this Turkish pediatric cohort, serum 25(OH)D levels were independently associated with AD severity after adjustment for age, sex, food allergy, and season. • A serum 25(OH)D cutoff of 20 ng/mL discriminated mild from moderate-to-severe AD, consistent with established clinical thresholds for vitamin D status.