Vitamin D Supplementation and Serum 25-Hydroxyvitamin D Response in Infants and Children: A Narrative Review

Vitamin D deficiency remains common among infants and young children, particularly in higher latitudes and among exclusively breast-fed infants. Although routine supplementation is widely recommended, variability in achieved serum 25-hydroxyvitamin D [25(OH)D] concentrations has been reported across pediatric populations. Understanding the consistency of biochemical response across diverse pediatric settings remains clinically relevant for both research and supplementation practice.

To summarize evidence from pediatric clinical studies utilizing a standardized vitamin D formulation and to assess the magnitude and consistency of serum 25(OH)D response across independent investigator-initiated studies.

Relevant studies were identified through company-supported research records and a supplementary PubMed search. Eligible publications were published between 2010 and 2020 and included infants or children ≤18 years receiving vitamin D supplementation with reported baseline and follow-up 25(OH)D concentrations. Studies were required to explicitly identify the study formulation and report serum 25(OH)D outcomes. A narrative synthesis approach was applied.

Seven studies (Canada, Australia, Vietnam, and Mongolia; total n ≈ 3,800) met inclusion criteria. Supplementation doses ranged from 400 IU/day to 14,000 IU/week across study durations of 1-12 months. Mean baseline 25(OH)D concentrations (≈53 nmol/L) increased to ≈75 nmol/L (mean Δ ≈22 nmol/L). Daily supplementation at 400 IU achieved sufficiency in the majority of infants, while higher-dose regimens produced proportionally greater increases. No study reported clinically significant adverse events attributable to supplementation.

Vitamin D supplementation produced consistent and clinically meaningful increases in serum 25(OH)D concentrations across diverse pediatric populations. The approximately 20-25 nmol/L increase observed across the included studies was broadly consistent with published pediatric vitamin D supplementation literature. These findings support current supplementation practices while highlighting the reproducibility of biochemical response across independent pediatric research settings.