Seasonal 25-hydroxy Vitamin D3 Variations in School-aged Children from Santiago de Chile

Helena Poggi; Gonzalo Dominguez; Arancibia Monica; Rosario Moore; Ivonne D'Apremont; Sandra Solari; Fidel Allende; Sofia Sifaqui; Hernan Garcia; Alejandro Martinez-Aguayo

Introduction: The main role of Vitamin D (VitD) is the regulation of calcium, which is also regulated by the parathyroid hormone (PTH), and phosphate metabolism. The main source of the more biologically active 25-hydroxy-Vitamin D3 (25OHVitD3) comes from the action of ultraviolet light on the skin.

Aim: To determine if there are differences in concentrations of 25OHVitD3, calcium and PTH in school-aged children throughout the four seasons

Subjects and Methods: Children 5-8 years old with no Vitamin D supplementation were recruited in different urban areas of Santiago de Chile (latitude -33.4372). 25OHVitD3 was measured by Liquid Chromatography-Mass Spectrometry, PTH by an automated immunoassay and calcium by a colourimetric automated assay. A One-way ANOVA was conducted to compare the 25OHVitD3, PTH and calcium concentrations and the Tukey's multiple comparison test to establish which mean was different from the other.

Results: 133 children were recruited during the four seasons by chance. No differences were found in age (P=0,419), height Z-score (P=0,466) or Body Mass Index (P=0,962) among the groups. Results for calcium, PTH and 25OHD3 are shown in the table below.


	Summer (n=41)	Autumn (n=28)	Winter (n=35)	Spring (n=29)	P (Anova)
Calcium (mg/dL)	9.92 ±0.37	9.89 ±0.26	9.89 ±0.28	10.00 ±0.27	0.425
PTH (pg/mL)	25.9 ±6.3	36.1 ±12.6	36.9 ±9.4	36.7 ±11.3	<0.001
25OHVitD3 (ng/mL)	31.2 ±6.7	24.2 ±4.9	21.5 ±5.7	25.7 ±7.7	<0.001

Compared to summer, mean differences in 25OHVitD3 concentrations were as follows: 5.4 ng/mL higher than in spring (95% CI: 1.3-9.5 ng/mL, P= 0.0045), 6.9 ng/ml higher than in autumn (95% CI: 2.8-11.1 ng/mL, P= 0.0001) and 9.6 ng/mL higher than in winter (95% CI: 5.7-13.5 ng/mL, P <0.0001). In comparison to summer, PTH concentrations were 10.8 pg/mL lower than in spring (95% CI: 5.3 to 16.3 pg/mL, P <0.0001), 8.3 pg/mL lower than in autumn (95% CI: 2.7 to 13.9 pg/ mL, P= 0.001) and 11.1 pg/mL lower than in winter (95%CI: 5.9 to 16.3 pg/mL, P <0.0001).

Conclusions: In autumn and winter, 25OHVitD3 concentrations decrease importantly, triggering an increase in PTH, in order to maintain calcium concentration. In regions where no Vitamin D supplementation is performed but where relatively prolonged winters are observed, as in Santiago de Chile and further south, reduced exposure to sunlight can lead to lower levels of vitamin D at least in school-aged children.

ESPE Abstracts

P2-46