Vitamin D status in adolescents: seasonal variations and effects of vitamin D-3 supplementation during winter.

Background. - Recently, 25 hydroxyvitamin D (25 OHD) blood concentrations m easured in adolescents during or at the end of winter were found very low. A concomitant stimulation of parathyroid function,vas observed. The aim of the present study was to test the biological effects of a treatment with vi tamin D-3 during winter. Populations and methods, - The effects of vitamin D-3 supplementation (100, 000 IU, twice, at the end of November and of January) were assessed in 24 m ale Caucasian adolescents (mean age +/- SD:14 y 6 m +/- 9 m). They were pup ils in a lad-jockeys training center located in the countryside near Chanti lly (49 degrees northern latitude). Blood concentrations of 25 OHD, calcium and intact parathormone (PTH) were measured three times: before each oral intake of vitamin D-3 and 2 months after the last intake (March). A group o f 32 male adolescents (mean age +/- SD:14 y 9 m +/- 6 m), pupils in the sam e center, receiving no vitamin D and sampled in November and in March, serv ed as controls. Results. - In March, mean concentrations of 25 OHD (8.36 +/- 2.73 mu g/L) w ere very low in vitamin D-not supplemented adolescents since 34% had levels less than 6 mu g/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 D-3 25 OND serum concentrations measured in January (17.5 +/- 3.2 mu g/L) and in March (18.7 +/- 4.0 mu g/L) remained at a leve l not very different from that measured in November (16.6 +/- 3.8 mu g/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) rema ined at their basal level as well. Conclusions. - The observation that, after winter, a relatively large numbe r of adolescents presented low concentrations of 25 OHD suggests that, duri ng 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 D-3 could maintain the vitamin D status at its initial level. T he efficiency of such a prophylactic treatment is also assessed by its effe ct on parathyroid function. (C) 1998 Elsevier, Paris.