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 .
Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol.
BACKGROUND The cholecalciferol inputs required to achieve or maintain any given serum 25-hydroxycholecalciferol concentration are not known , particularly within ranges comparable to the probable physiologic supply of the vitamin . OBJECTIVES The objectives were to establish the quantitative relation between steady state cholecalciferol input and the result ing serum 25-hydroxycholecalciferol concentration and to estimate the proportion of the daily requirement during winter that is met by cholecalciferol reserves in body tissue stores . DESIGN Cholecalciferol was administered daily in controlled oral doses labeled at 0 , 25 , 125 , and 250 micro g cholecalciferol for approximately 20 wk during the winter to 67 men living in Omaha ( 41.2 degrees N latitude ) . The time course of serum 25-hydroxycholecalciferol concentration was measured at intervals over the course of treatment . RESULTS From a mean baseline value of 70.3 nmol/L , equilibrium concentrations of serum 25-hydroxycholecalciferol changed during the winter months in direct proportion to the dose , with a slope of approximately 0.70 nmol/L for each additional 1 micro g cholecalciferol input . The calculated oral input required to sustain the serum 25-hydroxycholecalciferol concentration present before the study ( ie , in the autumn ) was 12.5 micro g ( 500 IU)/d , whereas the total amount from all sources ( supplement , food , tissue stores ) needed to sustain the starting 25-hydroxycholecalciferol concentration was estimated at approximately 96 micro g ( approximately 3800 IU)/d . By difference , the tissue stores provided approximately 78 - 82 micro g/d . CONCLUSIONS Healthy men seem to use 3000 - 5000 IU cholecalciferol/d , apparently meeting > 80 % of their winter cholecalciferol need with cutaneously synthesized accumulations from solar sources during the preceding summer months . Current recommended vitamin D inputs are inadequate to maintain serum 25-hydroxycholecalciferol concentration in the absence of substantial cutaneous production of vitamin
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 .