Statut vitaminique D de l’adolescent: variations saisonnières et effets d’une supplémentation hivernale par la vitamine D3

Abstract

Recently, 25 hydroxyvitamin D (25 OHD) blood concentrations measured in adolescents during or at the end of winter were found very low. A concomitant stimulation of parathyroid function was observed. The aim of the present study was to test the biological effects of a treatment with vitamin D3 during winter. The effects of vitamin D3 supplementation (100,000 IU, twice, at the end of November and of January) were assessed in 24 male Caucasian adolescents (mean age +/- SD: 14 y 6 m +/- 9 m). They were pupils in a lad-jockeys training center located in the countryside near Chantilly (49 degrees northern latitude). Blood concentrations of 25 OHD, calcium and intact parathormone (PTH) were measured three times: before each oral intake of vitamin D3 and 2 months after the last intake (March). A group of 32 male adolescents (mean age +/- SD: 14 y 9 m +/- 6 m), pupils in the same center, receiving no vitamin D and sampled in November and in March, served as controls. In March, mean concentrations of 25 OHD (8.36 +/- 2.73 micrograms/L) were very low in vitamin D-not supplemented adolescents since 34% had levels less than 6 micrograms/L. In March, PTH concentrations (40.5 +/- 12.2 ng/L) were significantly (P = 0.0001) higher than in November (28.8 +/- 9.9 ng/L). In boys receiving vitamin D3 25 OHD serum concentrations measured in January (17.5 +/- 3.2 micrograms/L) and in March (18.7 +/- 4.0 micrograms/L) remained at a level not very different from that measured in November (16.6 +/- 3.8 micrograms/L). During the same period, calcium and PTH concentrations (32.2 +/- 11.7 ng/L in November; 32.4 +/- 14.3 in January and 32.9 +/- 13.5 ng/L in March) remained at their basal level as well. The observation that, after winter, a relatively large number of adolescents presented low concentrations of 25 OHD suggests that, during winter, usual dietary intakes and/or vitamin D stores are not sufficient to provide for their needs. Administration of two oral doses of 100,000 IU of vitamin D3 could maintain the vitamin D status at its initial level. The efficiency of such a prophylactic treatment is also assessed by its effect on parathyroid function.