Effect of Vitamin C on Allergy Skin Test

Study Overview
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Brief Summary
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This study will assess the effect of taking vitamin C on allergy skin test.

Detailed Description
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Allergic rhinitis (AR) is an Immunoglobulin E (IgE) mediated inflammation of the nasal cavity. House dust mite is the most common causative allergen. The skin prick test is the preferred method to confirm allergy. This test is interpreted by measuring the skin wheal reaction in response to allergen application and histamine. Prior studies have shown that Vitamin C may have antihistamine effect that may reduce the wheal reaction in skin prick test thus cause difficulties to interpret the results. Current guidelines do not recommend cessation of vitamin C prior to skin prick test. This will require further study in order to further understand the effect of vitamin C in commercially available dose on the skin prick test wheal reaction. In this randomized placebo controlled trial, consecutive participant visiting the ENT clinic with allergic rhinitis and prior positive skin prick test towards dust mite will be screened for inclusion and exclusion criteria. Participants will either receive vitamin C 1000mg daily for 7 days or placebo. The skin prick test will be performed after one week of intervention and the area of the wheal reaction area (mm2) and longest diameter (mm) recorded. This will be compared between the two groups. The expected outcome is that participants with oral supplementation of vitamin C will have reduced SPT wheal reaction compared to placebo group.

Official Title
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The Effect of Vitamin C on the Skin Prick Test Wheal Reaction

Conditions
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Rhinitis, Allergic, Allergy

Intervention / Treatment
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* Dietary Supplement: Ascorbic acid 1000mg
* Other: Placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Participants above 18-years old Participants with history at least 2 symptoms of rhinitis triggered by dust Positive SPT to Dermatophagoides pteronyssinus with wheal reaction of at least 5 mm done within the past 1 year. Exclusion Criteria: Prior skin prick test result form do not include a tracing of the wheal reaction. Prior skin prick test was not performed in HCTM. Participants who are actively smoking or who have smoked cigarette or vaped in the past 6 months Participants with skin conditions affecting the volar aspects of the arm. Participants on beta-blockers Participants contraindicated for skin prick test (pregnancy, history of anaphylaxis, poorly controlled asthma) Participants on long term supplements (multivitamin, traditional supplement) Participants contraindicated for vitamin c (vitamin c allergy, kidney dysfunction, history of kidney or bladder stones, hyperuricemia, thalassemia, G6PD deficiency, sickle cell disease, hamatochromatosis) Participants at risk of vitamin C deficiency (hyperthyroidism, elderly, beastfeeding, diarrhoea, restricted diet secondary to inflammatory bowel disease, anorexia or cancer)

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Diagnostic
Allocation: Randomized
Intervention Model: Parallel Assignment
Interventional Model Description: Participant assigned to only one intervention per arm either vitamin C or placebo tablets
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Vitamin C<br>Commercially available Tablet Vitamin C 1000mg per day for 7 days | Dietary Supplement: Ascorbic acid 1000mg<br>* Health supplement<br>* Other names: VItamin C;|
| Placebo Comparator: Placebo<br>Glucose chewable table 1x per day for seven days | Other: Placebo<br>* Glucose chewable tablet without any ascorbic acid<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Skin prick test wheal area of vitamin C group compared to placebo | Skin wheal reaction is measured using computer software. Day 8 wheal area of vitamin C group compared to placebo. | Day 8 | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Skin prick test wheal reaction at day 8 of intevention compraed to prior skin prick test done as standard of care | Skin wheal reaction are is measured from prior skin test record (baseline) and at day 8 skin test repeated and measured. Area at day 7 - baseline. | Day 8 | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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ascorbic acid, skin prick test, vitamin C, antihistamine