Randomized trial of vitamin d supplementation and risk of acute
respiratory infection in mongolia. Observational studies suggest
that serum levels of 25-hydroxyvitamin D (25[OH]D) are inversely
associated with acute respiratory infections (ARIs). We
hypothesized that vitamin D supplementation of children with
vitamin D deficiency would lower the risk of ARIs. By using
cluster randomization, classrooms of 744 Mongolian
schoolchildren were randomly assigned to different treatments in
winter (January-March). This analysis focused on a subset of 247
children who were assigned to daily ingestion of unfortified
regular milk (control; n = 104) or milk fortified with 300 IU of
vitamin D(3) (n = 143). This comparison was double-blinded. The
primary outcome was the number of parent-reported ARIs over the
past 3 months. At baseline, the median serum 25(OH)D level was 7
ng/mL (interquartile range: 5-10 ng/mL). At the end of the
trial, follow-up was 99% (n = 244), and the median 25(OH)D
levels of children in the control v