Vitamin D status in Norwegian children and associations between child vitamin D status, dietary factors, and maternal vitamin D status

Background and aims: There is limited data regarding the vitamin D status of infants and young children in Norway. We aimed to assess vitamin D status among Norwegian children at approximately 6 and 12 months of age and explore associations between child vitamin D status, dietary factors, and maternal vitamin D status. Methods: Mothers/parents completed a food frequency questionnaire for their 6/12-month-old child. Dried blood spot samples were collected from the mother and child. Results: The mean serum 25-hydroxyvitamin D (S-25(OH)D) concentration was 81 nmol/L (standard deviation [SD] 22 nmol/L) for 6-month-old children (n = 84) and 72 nmol/L (SD 22 nmol/L) for 12-month-old children (n = 56) (P = 0.03 for difference between age groups). In the younger and older age groups, 94 and 88% of the children, respectively, had a S-25(OH)D concentration ≥ 50 nmol/L. The mean dietary vitamin D intake was 12 μg/day for the 6-month-olds and 14 μg/day for the 12-month-olds. Adjusted linear regression models showed that for every μg/day increase in dietary vitamin D intake, serum 25(OH)D (nmol/L) increased by around one nmol/L for both age groups (P = 0.002 for the younger age group and P = 0.04 for the older age group). Use of vitamin D supplements was associated with higher S-25(OH)D concentrations in both age groups, while a higher S-25(OH)D concentration among formula users was found only in the youngest age group. Breastfeeding was not associated with S-25(OH)D concentration in either age group. Small positive correlations between child and maternal vitamin D status were observed for both the younger (r = 0.22) and the older (r = 0.28) age groups (P = 0.04 for both groups). Conclusion: While there was a wide range in S-25(OH)D concentrations among children, most were within the sufficient range. Adequate vitamin D intake should be encouraged both in the first and second year of life.