Effect of High-Dose Vitamin D Supplementation on Upper Respiratory Tract Infection Symptom Severity in Healthy Children.

BACKGROUND: Observational studies support the role of vitamin D in reducing viral upper respiratory tract infection (URTI) symptom severity in adults and children. This study assessed whether wintertime high-dose vitamin D supplementation (2000 IU/day) reduces URTI symptom severity compared with standard-dose (400 IU/day) supplementation in preschool children. Secondary objectives were to assess effects of high-dose supplementation on outpatient physician visits, emergency department (ED) visits and antibiotic prescriptions for URTI. METHODS: This was a secondary analysis of a multisite randomized clinical trial involving 703 healthy 1- to 5-year-old children in Toronto, Canada. High-dose or standard-dose oral vitamin D was randomly assigned for 1 winter season. For each URTI, parents completed symptom checklists based on the Canadian Acute Respiratory and Flu Scale. Symptom severity, frequency of outpatient visits, ED visits and antibiotic prescriptions for URTI between groups were analyzed using negative binomial regression. RESULTS: URTI symptom severity was not reduced in the high-dose vs. standard-dose group [incidence rate ratio (IRR) = 0.97; 95% confidence interval (CI): 0.76-1.23]. High-dose vitamin D did not decrease frequency of outpatient visits (IRR = 1.16; 95% CI: 0.84-1.60), ED visits (IRR = 1.17; 95% CI: 0.57-2.40) or antibiotic prescriptions (IRR=1.02; 95% CI: 0.61-1.72). Serum 25-hydroxyvitamin D was higher in the high-dose group (48.7 ng/mL; 95% CI: 46.9-50.5) than the standard-dose group (36.8 ng/mL; 95% CI: 35.4-38.2; P < 0.001). CONCLUSIONS: High-dose vitamin D supplementation did not reduce URTI symptom severity, outpatient visits, ED visits or antibiotic prescriptions relative to standard-dose. These results do not support vitamin D supplementation above the standard recommended dose for reducing URTI symptoms in children.