A cross-sectional study was performed from January 2013 to September 2014 in the Pediatric Chest Clinic of the Department of Pediatrics at All India Institute of Medical Sciences (AIIMS), New Delhi, India. Children with physician-diagnosed asthma, aged 5-15 years, who had been in regular follow-up in the clinic for at least previous six months were enrolled into the study after ruling out chronic illness, clinical rickets or evidence of vitamin D supplementation in last six months, and after getting informed written consent. We planned to enroll a convenience sample of 100 children. The study protocol was approved by the Ethics Committee of the institute.

Data were collected on structured performa and managed using MS Excel software. Statistical analysis was performed using Stata 11.0 (Stata Corp, College Station, TX). We used descriptive statistics for the characteristics of the subjects. Fisher’s exact test/ chi-squared test were used for proportions. For continuous variables, ANOVA or Kruskal-Wallis test were used to assess statistical significance based on the distribution of variable (normal and non-normal, respectively). Vitamin D levels in children with different levels of control were compared by Kruskal-Wallis equality of population rank test.

A total of 108 children were enrolled into the study; 3 children were excluded from analysis because blood sample was not collected. The characteristics of the 105 enrolled children are shown in Table I.

TABLE I Comparison of Characteristics of Study Subjects Classified by the Asthma Control Status

Abbreviations: PFT: Pulmonary function test; SD: standard deviation; IQR: Interquartile range. 

Asthma status of 50 (47.6%) children were categorized as controlled, 32 (30.5%) as partly controlled, and 23 (21.9%) as uncontrolled. Table II compares the pulmonary function tests (PFT) values between these groups.

TABLE II  Pulmonary Function Tests in Children With Different Levels of Control of Asthma

The median (IQR) serum 25(OH)D level in the study participants was 9 (6,14) ng/mL. The median serum 25(OH)D levels were comparable in the three groups based on control of asthma. The prevalence of vitamin D deficiency in uncontrolled asthma group was higher with 78.2% children being vitamin D deficient (P=0.52) (Table III).

TABLE III  Vitamin D in Different Asthma Control Groups

The asthma control subgroups did not show any significant seasonal differences with the time of sampling. Median (IQR) cumulative inhaled steroid use were 423 (214.5, 684) mg, 456 (241.5, 576) mg, and 363 (330, 600) mg in deficient, insufficient and sufficient vitamin D status groups (P=0.98). Daily sunlight exposure was comparable in vitamin D sufficient participants and others (P=0.97).

Limitation of our study was a small sample size. We did not collect detailed information about dietary intakes, particularly vitamin D, and did not measure serum IgE levels. We did not have healthy children as controls as we compared the levels of vitamin D in children with various levels of control of asthma.

We conclude that there is unlikely to be any association between vitamin D levels and the control of asthma in children.

Contributors: TKK: study design, data collection and writing of manuscript; RL, SKK: designed the study, analyzed the data and wrote the manuscript; NG: laboratory assays and writing of manuscript.

Funding: None; Competing interest: None stated.

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