Do sufficient vitamin D levels at the end of summer in children and adolescents provide an assurance of vitamin D sufficiency at the end of winter? A cohort study

J Pediatr Endocrinol Metab. 2017 Oct 26;30(10):1041-1046. doi: 10.1515/jpem-2017-0132.

Abstract

Background: The changes in serum 25-hydroxyvitamin D (25(OH)D) in adolescents from summer to winter and optimal serum vitamin D levels in the summer to ensure adequate vitamin D levels at the end of winter are currently unknown. This study was conducted to address this knowledge gap.

Methods: The study was conducted as a cohort study. Sixty-eight participants aged 7-18 years and who had sufficient vitamin D levels at the end of the summer in 2011 were selected using stratified random sampling. Subsequently, the participants' vitamin D levels were measured at the end of the winter in 2012. A receiver operating characteristic (ROC) curve was used to determine optimal cutoff points for vitamin D at the end of the summer to predict sufficient vitamin D levels at the end of the winter.

Results: The results indicated that 89.7% of all the participants had a decrease in vitamin D levels from summer to winter: 14.7% of them were vitamin D-deficient, 36.8% had insufficient vitamin D concentrations and only 48.5% where able to maintain sufficient vitamin D. The optimal cutoff point to provide assurance of sufficient serum vitamin D at the end of the winter was 40 ng/mL at the end of the summer. Sex, age and vitamin D levels at the end of the summer were significant predictors of non-sufficient vitamin D at the end of the winter.

Conclusions: In this age group, a dramatic reduction in vitamin D was observed over the follow-up period. Sufficient vitamin D at the end of the summer did not guarantee vitamin D sufficiency at the end of the winter. We found 40 ng/mL as an optimal cutoff point.

Keywords: 25-hydroxyvitamin D; adolescents; children; vitamin D deficiency.

MeSH terms

  • Adolescent
  • Age Factors
  • Child
  • Female
  • Humans
  • Male
  • Seasons*
  • Sex Factors
  • Sunlight
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / diagnosis*

Substances

  • Vitamin D
  • 25-hydroxyvitamin D