Severe vitamin D deficiency is associated with severe bone mineralisation defects, but the clinical significance of what is defined as mild or moderate deficiency is more controversial. Levels vary seasonally, being lower in winter, and healthy children often have levels below the designated reference range (currently 50 nmol/L). From association studies, vitamin D deficiency is thought to predispose to respiratory infection. In a randomised controlled trial, 99% of 247 apparently healthy Mongolian schoolchildren aged 9–10 years had vitamin D deficiency defined as a serum vitamin D level <20 ng/mL (50 nmol/L). The median was 7 ng/mL (17.5 nmol/L). Pill supplements were ineffective at raising vitamin D levels for other children in the study. However, children randomised to receive cow's milk fortified with 300 U vitamin D daily for 3 months had a mean post-supplementation vitamin D level of 18.9 ng/mL (47.5 nmol/L) compared with 7.2 ng/mL (18 nmol/L) for children who received unfortified milk. The main outcome measure, the incidence of respiratory virus infections, was approximately halved in association with vitamin D supplementation. This is one of very few papers to show that vitamin D supplementation can improve non-bone-related outcomes, presumably by improving innate immune function.
Reviewers: Craig Munns, firstname.lastname@example.org; David Isaacs, Children's Hospital at Westmead, Westmead, NSW, 2145