The researchers calculated that 33 people would need to take vitamin D supplements to prevent one acute respiratory tract infection. Benefit was greater in those receiving daily or weekly vitamin D without additional bolus doses (NNT=20), and the protective effects against acute respiratory tract infection in this group were strongest in those with profound vitamin D deficiency at baseline - <25 nmol/L baseline blood levels (NNT=4).
But in a linked editorial other academics, who recently questioned the evidence using vitamin D supplements to prevent disease, said that a clinically useful effect remains uncertain and requires confirmation in further “well designed, adequately powered” randomised controlled trials. The authors argued that the absolute risk reduction of 2% found in the study would not be a sufficient justification for most of the general population to take supplements. They said that the results should be viewed as “hypothesis generating only”.