Vitamin D Status and Its Determinants in a Paediatric Population in Norway

Recommendations for sufficient vitamin D intake in children were recently revised in Norway. However, optimal levels of vitamin D are still debated and knowledge on supplementation and vitamin D levels in healthy children in Norway is scarce. Therefore, we measured the plasma-concentration of 25-hydroxyvitamin D (25(OH)D) in children and adolescents attending the outpatient paediatric clinics in Innlandet Hospital Trust, Norway during two consecutive years (2015–2017). We recruited 301 children and adolescents aged 5 months to 18 years (mean 7.8, SD 4.4 years) for the study and obtained sample material for 25(OH)D measurements from 295 (98%). Information on diet, vitamin D supplementation, sun exposure, ethnicity, parental education and general health was collected by questionnaire. 25(OH)D levels were analysed and determinants for 25(OH)D were estimated by linear regression. 1.0% of the children had deficient levels (25(OH)D < 25 nmol/L) and 21.0% had insufficient levels (25–50 nmol/L). 25(OH)D levels ranging from 50 to 75 nmol/L were found among 38.3%, while 39.7% had levels above 75 nmol/L. The mean 25(OH)D level was 70.0 nmol/L (SD 23.4, range 17–142 nmol/L) with a significant seasonal variation with lowest levels in mid-winter and highest in late summer. In addition to seasonal variation independent determinants for 25(OH)D-levels were age of the child, parental ethnicity, vitamin D supplementation and soda consumption. Along with parental ethnicity other than Nordic, age was the strongest determinant of 25(OH)D, with adolescents having the lowest levels.