Characteristics of included studies.

Abbreviations: w, winter; sp, spring; su, summer; f, fall; NR, not reported; HDM, house dust mites; SIT, specific immunotherapy; ED, emergency department visits; AE, asthma exacerbations; AS, asthma severity/symptoms; ICS, inhaled corticosteroid use; β2, β2 agonist use; LF, lung function; VD, serum 25(OH)D concentration; AdvE, adverse events. a55 participants were randomized into three groups: pharmacotherapy group, SIT group, SIT + vitamin D group. Only SIT (n = 15) and SIT + vitamin D (n = 17) were included in this review (n = 32). b430 participants were randomized into vitamin D or placebo group. Only those who were previously diagnosed with asthma were used in the calculation of the RR presented in the meta-analysis (n = 230). c54 participants were randomized into three groups: placebo group, steroid group, steroid + vitamin D group. Only steroid group (n = 18) and steroid + vitamin D group (n = 18) were used (n = 36). dInformation obtained directly from authors. Characteristics of included studies.