This study will be an assessor-blind, randomized controlled trial in patients with CSU. The investigators will compared Vit D level in patients with Chronic spontaneous urticaria (CSU) and controls. Enrolled CSU patients with Vit D level <30ng/ml will be then randomized into three intervention arms in the ratio of 1:1:1. Patients belonging to intervention group A will be treated with low dose Vit D (2000 IU/day) for 12 weeks according to the Indian council of medical research (ICMR) guidelines. Intervention group B patients will be treated with high dose Vit D (60,000 IU/week) for 12 weeks and group C will not be given any Vit D supplements. All patients will be evaluated after 12 weeks. The urticaria activity score over 4 days (UAS4) will be used to assess the disease severity using the number of wheals and pruritus intensity based on the EAACI/GA2LEN/EDF guidelines. The patient's disease severity levels will be graded as mild (0-8), moderate (9-16), and severe (17-24).

This is a prospective, randomized, single-centre clinical study. Serum Vit D level will be assessed in all patients at baseline. Patients with Vit D level ≥30 will be excluded from the trial but included in the study and those with Vit D level <30 will be randomized into 3 groups A, B and C. Patients with Vit D level ≥30 will be categorized into Group D. Patients belonging to Group A will be treated with low dose Vit D (2000 IU/day) according to Indian council of medical research (ICMR) guidelines. Those in Group B will be treated with high dose Vit D (60,000 IU/week) and group C will not be given any Vit D supplements. Patients belonging to Group A and B will be treated for 12 weeks in order to safely restore Vit D and achieve a steady state. In addition levocetirizine, 10 mg will be given to all patients in groups to control urticaria symptoms. All patients will be treated according to EAACI/GA2LEN/EDF guidelines after 12 weeks. All participants will also be provided with rescue prednisone use for intolerable or uncontrolled symptoms. At 6 weeks and 12 weeks, a physician assessment (physician blinded to treatment arm) will be conducted to check if patients had intolerable symptoms or took rescue prednisolone 40 mg therapy. Safety monitoring will be completed throughout the entirety of the study. Specific stopping rules and discontinuation of the study included pregnancy, a serum Vit D level higher than 100 ng/mL, or a serum calcium level higher than 11 mg/dL. Patients will be followed for 6 weeks after the study completion and thereafter data analysis will be done in 3 steps:

Step 1: Comparison of serum Vit D level in CSU patients vs. controls Step 2 : Assessment of factors associated with Vit D deficiency in urticaria patients Step 3: Effect of Vit D supplementation (group A (low dose), group B (high dose), group C(no supplementation) on urticaria severity using UAS4

Inclusion Criteria:

• Adults >18 years of age, having urticaria episodes at least 2 days per week for 6 weeks or longer with/without angioedema.

Exclusion Criteria:

• Patients with only physical urticaria, only dermatographism, urticarial vasculitis, hereditary or acquired angioedema.
• Patients with BMI>25 kg/m2, dyslipidemia, diabetes, hypertension, pre-existing cardiovascular disease, cerebro-vascular accidents, hypothyroidism, smokers, and other systemic or cutaneous disorders including atopic dermatitis, psoriasis etc.
• Patients with hypercalcemia (>11 mg/dL), diabetes, renal insufficiency, hepatic disorders, hyperparathyroidism, sarcoidosis, other granulomatous disorders, malignancy.
• Pregnant and lactating women, patients who have taken Vit D supplementation in past 6 months.