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 .
Vitamin D3 and gargling for the prevention of upper respiratory tract infections: a randomized controlled trial
Background We undertook a 2X2 factorial , r and omized controlled trial ( RCT ) to assess whether vitamin D3 supplementation ( 10,000 international units per week ) versus placebo and gargling versus no gargling could prevent  viral  ,  clinical upper respiratory tract infection ( URTI ) in university students . Methods We r and omized 600 students into 4 treatment arms : 1 ) vitamin D3 and gargling , 2 ) placebo and gargling , 3 ) vitamin D3 and no gargling , and 4 ) placebo and no gargling . Students completed weekly electronic surveys and su bmi tted self-collected mid-turbinate nasal flocked swabs during September and October in 2010 or 2011 . Symptomatic students also completed an electronic symptom diary . The primary and secondary outcomes were the occurrence of symptomatic clinical URTI and laboratory confirmed URTI respectively . Results Of 600 participants , 471 ( 78.5 % ) completed all surveys while 43 ( 7.2 % ) completed none ; 150 ( 25.0 % ) reported clinical URTI . Seventy participants ( 23.3 % ) r and omized to vitamin D3 reported clinical URTI compared to 80 ( 26.7 % ) r and omized to placebo ( RR:0.79 , CI95:0.61 - 1.03 , p = 0.09 ) . Eighty-five participants ( 28.3 % ) r and omized to gargling reported clinical URTI compared to 65 participants ( 21.7 % ) r and omized to the no gargling arm ( RR:1.3 , CI95:0.92 - 1.57 , p = 0.19 ) . Laboratory testing identified 70 infections ( 46.7 per 100 URTIs ) . Vitamin D3 treatment was associated with a significantly lower risk for laboratory confirmed URTI ( RR : 0.54 , CI95:0.34 - 0.84 , p = 0.007 ) and with a significantly lower mean viral load measured as log10 viral copies/mL ( mean difference : -0.89 , CI95 : -1.7 , -0.06 , p = 0.04 ) . Fewer students assigned to gargling experienced laboratory confirmed URTI , however this was not statistically significant ( RR:0.82 , CI95:0.53 - 1.26 , p = 0.36 ) . Conclusions These results suggest that vitamin D3 is a promising intervention for the prevention of URTI . Vitamin D3 significantly reduced the risk of laboratory confirmed URTI and may reduce the risk of clinical infections . Trial registration Clinical Trials Registration : NCT01158560
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 .