This case-control study was conducted on 53 asthmatic patients and 53 healthy controls in Mofid hospital, Tehran during 2013. The selection of samples was based on simple census sampling method. The patients aged above 2 years who were diagnosed with asthma and hyperreactive airway disease, were included in the study. Asthma was diagnosed according to the EPR3 and GINA criteria [1, 13]. All included patients gave informed written consent and the study was approved by the ethics committee at Shahid Beheshti University of Medical Sciences (registration number: IR.SBMU. MSP.REC.1392.405). Human rights were respected in accordance with the Helsinki Declaration. The exclusion criteria were having disease or conditions which might affect serum level of vitamin D and or its metabolism, including chronic renal failure, metabolic disorder, malabsorption, cholestasis, refractory Rickets.
The control subjects were randomly selected from children without asthmatic children or other underlying disorders the baseline characteristics were collected from clinical checklist completed by interviewing parents and patients including gender, age, duration of asthma, and hospitalization rate. The level of serum vitamin D in both groups was measured by radioimmunoassay (RIA) method at the reference lab and was categorized as sufficient ( 30 ng/ml), insufficient (20 to 30 ng/ml), or deficient ( 20 ng/ml). The severity of asthma was also stratified according to the asthma guideline into four grades of intermittent or mild, moderate, severe persistent [14]. Also, the control status of asthma in patients group was classified as controlled, partially controlled, and uncontrolled based on GINA (Global Initiative for Asthma) criteria including daytime symptoms, limitation of activities, nocturnal symptoms, need for reliever or rescue inhaler, and lung function [13]. Moreover, the risk for appearance of symptoms was assessed based on the frequency of worsening symptoms need to use systemic corticosteroids according to the guidelines [1, 13].
For statistical analysis, Results were presented as mean?±?standard deviation (SD) for quantitative variables and were summarized by absolute frequencies and percentages for categorical variables. Categorical variables were compared using chi-square test or Fisher’s exact test when more than 20% of cells with expected count of less than 5 were observed. Quantitative variables were also compared with t test, ANOVA (Analysis of Variance) tests or Mann- Whitney U test. The association between quantitative variables was tested using the Pearson’s or Spearman’s correlation test. We used the multivariable regression modeling to assess the relation between vitamin D deficiency and severity of asthma with the presence of confounders. For the statistical analysis, the statistical software SPSS version 16.0 for windows (SPSS Inc., Chicago, IL) was used. P values of 0.05 or less were considered statistically significant.