Collectively , the evidence suggests that higher serum levels of 25(OH)D are associated with a reduced risk of asthma exacerbations , but there was little evidence to suggest an association with asthma incidence , prevalence or severity .
Asthma is a major public health issue .
The co-occurrence of the high prevalence of asthma and vitamin D deficiency documented globally in recent decades has prompted several investigations into a possible association between the two conditions .
The objective of this paper was to synthesize the evidence from studies that have measured the association between serum vitamin D  and asthma incidence , prevalence , severity and exacerbations .
Serum vitamin D levels and severe asthma exacerbations in the Childhood Asthma Management Program study.
BACKGROUND Asthma exacerbations , most often caused by respiratory tract infections , are the leading causes of asthma morbidity and comprise a significant proportion of asthma-related costs . Vitamin D status might play a role in preventing asthma exacerbations . OBJECTIVES We sought to assess the relationship between serum vitamin D levels and subsequent severe asthma exacerbations . METHODS We measured  25-hydroxyvitamin D levels in sera collected from 1024 children with mild-to-moderate persistent asthma at the time of enrollment in a multicenter clinical trial of children r and omized to receive budesonide , nedocromil , or placebo ( as-needed beta-agonists ) : the Childhood Asthma Management Program . Using multivariable modeling , we examined the relationship between baseline vitamin D levels and the odds of any hospitalization or emergency department visit over the 4 years of the trial . RESULTS Thirty-five percent of all subjects were  vitamin D insufficient , as defined by a level of 30 ng/mL or less 25-hydroxyvitamin D. Mean vitamin D levels were lowest in African American subjects and highest in white subjects . After adjusting for age , sex , body mass index , income , and treatment group , insufficient vitamin D status was associated with a higher odds of any hospitalization or emergency department visit ( odds ratio , 1.5 ; 95 % CI , 1.1 - 1.9 ; P = .01 ) . CONCLUSION Vitamin D insufficiency is common in this population of North American children with mild-to-moderate persistent asthma and is associated with higher odds of severe exacerbation over a 4-year period
Collectively , the evidence suggests that higher serum levels of 25(OH)D are associated with a reduced risk of asthma exacerbations , but there was little evidence to suggest an association with asthma incidence , prevalence or severity .
Asthma is a major public health issue .
The co-occurrence of the high prevalence of asthma and vitamin D deficiency documented globally in recent decades has prompted several investigations into a possible association between the two conditions .
The objective of this paper was to synthesize the evidence from studies that have measured the association between serum vitamin D  and asthma incidence , prevalence , severity and exacerbations .