Available evidence from this systematic review suggests that high dose vitamin D may prevent  asthma exacerbation .
CONTEXT Observational studies have suggested a relationship between vitamin D status and asthma-related respiratory outcomes .
The benefit of vitamin D supplementation for pulmonary function , symptoms and exacerbations is not well established .
OBJECTIVE To systematic ally review paediatric clinical trials investigating the role of vitamin D on asthma-related respiratory outcomes .
Vitamin D levels, lung function, and steroid response in adult asthma.
RATIONALE Patients with asthma exhibit variable response to inhaled corticosteroids ( ICS ) . Vitamin D is hypothesized to exert effects on phenotype and glucocorticoid ( GC ) response in asthma . OBJECTIVES To determine the effect of vitamin D levels on phenotype and GC response in asthma . METHODS Nonsmoking adults with asthma were enrolled in a study assessing the relationship between serum 25(OH)D ( vitamin D ) concentrations  and lung function , airway hyperresponsiveness ( AHR ) , and GC response , as measured by dexamethasone-induced expression of mitogen-activated protein kinase phosphatase (MKP)-1 by peripheral blood mononuclear cells . MEASUREMENTS AND MAIN RESULTS A total of 54 adults with asthma ( FEV(1 ) , 82.9 + /- 15.7 % predicted [ mean + /- SD ] , serum  vitamin D  levels of 28.1 + /- 10.2 ng/ml ) were enrolled . Higher vitamin D levels were associated with greater lung function , with a 22.7 ( + /-9.3 ) ml ( mean + /- SE ) increase in FEV(1 ) for each nanogram per milliliter increase in vitamin D ( P = 0.02 ) . Participants with vitamin D insufficiency ( < 30 ng/ml ) demonstrated increased AHR , with a provocative concentration of methacholine inducing a 20 % fall in FEV(1 ) of 1.03 ( + /-0.2 ) mg/ml versus 1.92 ( + /-0.2 ) mg/ml in those with vitamin D of 30 ng/ml or higher ( P = 0.01 ) . In ICS-untreated participants , dexamethasone-induced MKP-1 expression increased with higher vitamin D levels , with a 0.05 (+/-0.02)-fold increase ( P = 0.02 ) in MKP-1 expression observed for each nanogram per milliliter increase in vitamin D , a finding that occurred in the absence of a significant increase in IL-10 expression . CONCLUSIONS In asthma , reduced vitamin D levels are associated with impaired lung function , increased AHR , and reduced GC response , suggesting that supplementation of vitamin D levels in patients with asthma may improve multiple parameters of asthma severity and treatment response . Clinical trials registered with www . clinical trials.gov ( NCT00495157 , NCT00565266 , and NCT00557180 )
Available evidence from this systematic review suggests that high dose vitamin D may prevent  asthma exacerbation .
CONTEXT Observational studies have suggested a relationship between vitamin D status and asthma-related respiratory outcomes .
The benefit of vitamin D supplementation for pulmonary function , symptoms and exacerbations is not well established .
OBJECTIVE To systematic ally review paediatric clinical trials investigating the role of vitamin D on asthma-related respiratory outcomes .