Maternal Vitamin D Use During Pregnancy and Infant Supplementation as Determinants of Serum 25(OH)D Levels in Children Aged 6–24 Months

The complementary feeding period is a critical stage for infant nutrition and vitamin D status. This study aimed to determine whether maternal vitamin D use during pregnancy and infant supplementation predict serum 25(OH)D levels in children aged 6–24 months. This analytical cross-sectional study included 267 mother–child pairs between November 2023 and February 2024. Sociodemographic characteristics, feeding practices, vitamin D supplementation habits, and serum 25(OH)D levels were collected. Group comparisons were performed using independent samples t-tests and one-way ANOVA, and predictors of serum 25(OH)D levels were assessed using multiple linear and multinomial logistic regression analyses. The mean age of the children was 13.5 ± 4.8 months. Regular vitamin D supplementation was reported in 67.0% of children, whereas 11.3% used supplementation irregularly and 21.7% received none. Vitamin D deficiency was detected in 20.6% of children and insufficiency in 10.5%. Children whose mothers used vitamin D during pregnancy had significantly higher serum 25(OH)D levels (p < 0.001). In the regression model, maternal vitamin D use during pregnancy, infant supplementation status, and vitamin D dose were significant predictors of serum 25(OH)D levels (R² = 0.346, p < 0.001). Maternal non-use of vitamin D during pregnancy increased the risk of vitamin D deficiency (OR = 15.27, 95% CI 5.82–40.02), and irregular supplementation was associated with markedly higher odds of deficiency (OR = 28.16, 95% CI 8.21–96.64). Conclusion : Maternal vitamin D use during pregnancy and regular infant supplementation are key determinants of optimal serum 25(OH)D levels in early childhood.