Distribution of Vitamin D Metabolites in Early Childhood: Findings from a Multicenter Belgian Cross-Sectional Study

Vitamin D metabolism is essential for calcium and phosphate homeostasis, yet reference values for its key metabolites in early childhood are lacking. This study aimed to establish percentile-based intervals for 1,25-dihydroxyvitamin D [1,25(OH)₂D], 24,25-dihydroxyvitamin D [24,25(OH)₂D], and the Vitamin D Metabolite Ratio (VMR= 24,25(OH)₂D/25(OH)D x 100%) in healthy, well vitamin D-supplemented children under 2 years of age, providing a benchmark for disorders such as idiopathic infantile hypercalcemia.

This cross-sectional study analyzed blood samples from 208 healthy full-term children undergoing elective minor surgery or diagnostic procedures at four Belgian hospitals. 25(OH)D and 24,25(OH)₂D were measured by LC-MS/MS, and 1,25(OH)₂D by IDS-iSYS immunoassay. The VMR (24,25(OH)₂D₃ / 25(OH)D₃ × 100%) was calculated. The intervals were expressed as percentiles and 95% confidence intervals. Associations between clinical factors and vitamin D markers were assessed using univariate and multivariate regression analyses.

Population-specific percentile-based intervals applicable to vitamin D-supplemented infants (2.5th - 97.5th percentiles) were 35.57 - 148.55 pg/mL for 1,25(OH)₂D, 0.50-6.61 ng/mL for 24,25(OH)₂D and 1.95-15.74 % for 24,25(OH)₂D₃ / 25(OH)D₃ × 100%. Older age was associated with lower 1,25(OH)₂D levels. The concentration of 25(OH)D was higher in older children, boys, non-Caucasians, and those with higher vitamin D supplement intake. The concentration of 24,25(OH)₂D was positively associated with supplementation. After adjustment for relevant covariates, multivariable analysis demonstrated independent associations between VMR, ethnicity, and vitamin D supplementation, whereby Caucasian ethnicity and vitamin D supplementation were associated with higher VMR values.

These data provide the first pediatric percentile-based intervals for vitamin D metabolites in well vitamin D-supplemented children under two years of age, demonstrating the influence of age, body composition, supplementation, and ethnicity. These ranges can support the early diagnosis of metabolic bone disorders and guide clinical decision-making.