Association of vitamin D supplementation with respiratory tract infection in infants

Abstract

Vitamin D deficiency has been reported to be associated with respiratory tract infection (RTI). However, evidence regarding the effects of vitamin D supplementation on susceptibility of infants to RTI is limited. In this prospective birth cohort study, we examined whether vitamin D supplementation reduced RTI risk in 2,244 infants completing the follow-up from birth to 6 months of age. The outcome endpoint was the first episode of paediatrician-diagnosed RTI or 6 months of age when no RTI event occurred. Infants receiving vitamin D supplements at a daily dose of 400-600 IU from birth to the outcome endpoint were defined as vitamin D supplementation and divided into four groups according to the average frequency of supplementation: 0, 1-2, 3-4, and 5-7 days/week. We evaluated the relationship between vitamin D supplementation and time to the first episode of RTI with Kaplan-Meier plots. The associations of vitamin D supplementation with infant RTI, lower RTI (LRTI), and RTI-related hospitalization were assessed using modified Poisson regression. The median time to first RTI episode was 60 days after birth (95% CI [60, 90]) for infants without supplementation and longer than 6 months of age for infants with supplementation (p < .001). We observed inverse trends between supplementation frequency and risk of RTI, LRTI, and RTI-related hospitalization (p for trend < .001), with the risk ratios in the 5-7 days/week supplementation group of 0.46 (95% CI [0.41, 0.50]), 0.17 (95% CI [0.13, 0.24]), and 0.18 (95% CI [0.12, 0.27]), respectively. These associations were significant and consistent in a subgroup analysis stratified by infant feeding.

Keywords: feeding; infant; respiratory tract infection; vitamin D supplementation.

Figure 1

Kaplan–Meier curves^a for time to first RTI developed by infants stratified by vitamin D supplementation, according to feeding during the first 6 months of life. The solid line is the Kaplan–Meier curve for the vitamin D supplementation group, and the dotted line for the group without supplementation. ^aTinted region indicates 95% confidence intervals around the proportion of infants free of RTI. ^bMedian time indicates the time by which 50% of infants were found experiencing the first RTI episode. ^cEstimation was not possible because the median time was longer than the 6‐month follow‐up period of the study. Abbreviations: CI, confidence interval; RTI, respiratory tract infection