Abstract
BACKGROUND: Chronic urticaria (CU), especially chronic spontaneous urticaria (CSU), is a long-term inflammatory skin condition marked by wheals and/or angioedema lasting over six weeks. Emerging evidence suggests a link between vitamin D deficiency and immune dysregulation associated with CU. Given vitamin D's immunomodulatory and anti-inflammatory effects, this review explores the therapeutic potential of vitamin D supplementation in CU management. METHODS: A systematic review was conducted in accordance with PRISMA guidelines Electronic databases (PubMed, Scopus, Web of Science, and Google Scholar) were searched using relevant keywords. Studies included were randomized controlled trials (RCTs), case-control, and observational studies assessing serum vitamin D levels or supplementation in patients with CU. Data extraction and bias assessment were independently conducted using standardized tools: the Cochrane Risk of Bias Tool and the Newcastle-Ottawa Scale. RESULTS: Eleven studies involving 1,491 participants were included. Most studies demonstrated significantly lower serum 25(OH)D levels in patients with CU compared to healthy controls. Vitamin D supplementation, particularly in individuals with a deficiency, was associated with reductions in urticaria activity scores, symptom severity, and improved quality of life. High-dose regimens (e.g., 4,000 IU/day or 60,000 IU/week) appeared more effective. However, results varied due to heterogeneity in study design, dosage, and patient characteristics. CONCLUSION: Vitamin D supplementation may serve as a safe, accessible adjunct to standard CU treatment, particularly for those with confirmed deficiency. While evidence suggests potential benefits, further high-quality RCTs are needed to establish causality, optimal dosing, and long-term efficacy.