Conclusions Vitamin D supplementation  was safe and it protected against acute respiratory tract infection overall .
Patients who were very vitamin D deficient and those not receiving bolus doses experienced the most benefit .
Objectives To assess the overall effect of vitamin D supplementation on  risk of acute respiratory tract infection  , and to identify factors modifying this effect .
Effect of vitamin D3 supplementation on upper respiratory tract infections in healthy adults: the VIDARIS randomized controlled trial.
CONTEXT Observational studies have reported an inverse association between serum 25-hydroxyvitamin D ( 25-OHD ) levels and incidence of upper respiratory tract infections ( URTIs ) . However , results of clinical trials of vitamin D supplementation have been inconclusive . OBJECTIVE To determine the effect of vitamin D supplementation on incidence and severity of URTIs in healthy adults . DESIGN , SETTING , AND PARTICIPANTS R and omized , double-blind , placebo-controlled trial conducted among 322 healthy adults between February 2010 and November 2011 in Christchurch , New Zeal and . INTERVENTION Participants were r and omly assigned to receive an initial dose of 200,000 IU oral vitamin D3 , then 200,000 IU 1 month later , then 100,000 IU monthly ( n = 161 ) , or placebo administered in an identical dosing regimen ( n = 161 ) , for a total of 18 months . MAIN OUTCOME MEASURES The primary end point was number of URTI episodes . Secondary end points were duration of URTI episodes , severity of URTI episodes , and number of days of missed work due to URTI episodes . RESULTS The mean baseline 25-OHD level of participants was 29 ( SD , 9 ) ng/mL. Vitamin D supplementation result ed in an increase in serum 25-OHD levels that was maintained at greater than 48 ng/mL throughout the study . There were 593 URTI episodes in the vitamin D group and 611 in the placebo group , with no statistically significant differences in the number of URTIs per participant ( mean , 3.7 per person in the vitamin D group and 3.8 per person in the placebo group ; risk ratio , 0.97 ; 95 % CI , 0.85 - 1.11 ) , number of days of missed work as a result of URTIs ( mean , 0.76 days in each group ; risk ratio , 1.03 ; 95 % CI , 0.81 - 1.30 ) , duration of symptoms per episode ( mean , 12 days in each group ; risk ratio , 0.96 ; 95 % CI , 0.73 - 1.25 ) , or severity of URTI episodes . These findings remained unchanged when the analysis was repeated by season and by baseline 25-OHD levels . CONCLUSION In this trial , monthly administration of 100,000 IU of vitamin D did not reduce the incidence or severity of URTIs in healthy adults . TRIAL REGISTRATION anzctr.org.au Identifier : ACTRN12609000486224
Conclusions Vitamin D supplementation  was safe and it protected against acute respiratory tract infection overall .
Patients who were very vitamin D deficient and those not receiving bolus doses experienced the most benefit .
Objectives To assess the overall effect of vitamin D supplementation on  risk of acute respiratory tract infection  , and to identify factors modifying this effect .