Meta- analysis of a modest number of trials in people with predominantly mild to moderate asthma suggests that vitamin D is likely to reduce both the risk of severe asthma exacerbation and healthcare use .
Children and people with frequent severe asthma exacerbations were under-represented ; additional primary trials are needed to establish whether vitamin D can reduce the risk of severe asthma exacerbation in these groups
BACKGROUND Several clinical trials of vitamin D to prevent  asthma exacerbation  and improve  asthma control  have been conducted in children and adults , but a meta- analysis restricted to double-blind , r and omised , placebo-controlled trials of this intervention is lacking .
OBJECTIVES To evaluate the efficacy of administration of vitamin D and its hydroxylated metabolites in reducing the risk of severe asthma exacerbations ( defined as those requiring treatment with systemic corticosteroids ) and improving asthma symptom control .
Double-blind randomised placebo-controlled trial of bolus-dose vitamin D3 supplementation in adults with asthma (ViDiAs)
Rationale Asthma exacerbations are commonly precipitated by viral upper respiratory infections ( URIs ) . Vitamin D insufficiency associates with susceptibility to URI in patients with asthma . Trials of vitamin D in adults with asthma with incidence of exacerbation and URI as primary outcome are lacking . Objective To conduct a r and omised controlled trial of vitamin D3 supplementation for the prevention of asthma exacerbation and URI ( co primary outcomes ) . Measurements and methods 250 adults with asthma in London , UK were allocated to receive six 2-monthly oral doses of 3 mg vitamin D3 ( n=125 ) or placebo ( n=125 ) over 1 year . Secondary outcomes included asthma control test and St George 's Respiratory Question naire scores , fractional exhaled nitric oxide and concentrations of inflammatory markers in induced sputum . Subgroup analyses were performed to determine whether effects of supplementation were modified by baseline vitamin D status or genotype for 34 single nucleotide polymorphisms in 11 vitamin D pathway genes . Main results 206/250 participants ( 82 % ) were vitamin D insufficient at baseline . Vitamin D3 did not influence time to first severe exacerbation ( adjusted HR 1.02 , 95 % CI 0.69 to 1.53 , p=0.91 ) or first URI ( adjusted HR 0.87 , 95 % CI 0.64 to 1.16 , p=0.34 ) . No clinical ly important effect of vitamin D3 was seen on any of the secondary outcomes listed above . The influence of vitamin D3 on co primary outcomes was not modified by baseline vitamin D status or genotype . Conclusions Bolus-dose vitamin D3 supplementation did not influence time to exacerbation or URI in a population of adults with asthma with a high prevalence of baseline vitamin D insufficiency . Trial registration number NCT00978315 ( Clinical Trials.gov )
Meta- analysis of a modest number of trials in people with predominantly mild to moderate asthma suggests that vitamin D is likely to reduce both the risk of severe asthma exacerbation and healthcare use .
Children and people with frequent severe asthma exacerbations were under-represented ; additional primary trials are needed to establish whether vitamin D can reduce the risk of severe asthma exacerbation in these groups
BACKGROUND Several clinical trials of vitamin D to prevent  asthma exacerbation  and improve  asthma control  have been conducted in children and adults , but a meta- analysis restricted to double-blind , r and omised , placebo-controlled trials of this intervention is lacking .
OBJECTIVES To evaluate the efficacy of administration of vitamin D and its hydroxylated metabolites in reducing the risk of severe asthma exacerbations ( defined as those requiring treatment with systemic corticosteroids ) and improving asthma symptom control .