Serum 25-Hydroxy Vitamin D Levels in Japanese Infants with Respiratory Syncytial Virus Infection Younger than 3 Months of Age.

Low blood levels of vitamin D have been reported in children who have frequent respiratory tract infections. We measured serum concentrations of 25-hydroxy (OH) vitamin D in Japanese infants under 3 months of age who had respiratory syncytial virus (RSV) infection. Serum levels of 25-OH vitamin D in the 10 infants, excluding those with underlying diseases, were between < 4 and 29.8 ng/mL. In 8 out of 10 subjects (80.0%), serum 25-OH vitamin D levels were lower than 20 ng/mL. There was no statistically significant association between the levels of 25-OH vitamin D and age, duration of admission, respiratory severity score, white blood cell count, blood gas levels, and N-terminal pro-natriuretic peptide levels. Levels of serum 25-OH vitamin D in children who required hospitalization owing to RSV infection were low, indicating deficiency. These results suggest that vitamin D deficiency affects the susceptibility to RSV infection, but not the severity of the infection.