Wintertime vitamin D deficiency in male adolescents: Effect on parathyroidfunction and response to vitamin D-3 supplements

The first part of this study consisted of an 18 month follow-Lip of the vit amin D status and parathyroid function in a group of 54 French male adolesc ents., aged from 13 to 16 years old and all pupils of a jockey training sch ool. During the IS month period four samplings were made, one every 6 month s. The first was during September of the first year, the second and third d uring March and October of the second year, and the last in March of the th ird year. Therefore we had two main periods: summer and winter. The summer 25-hydroxyvitamin D (25(OH)D) concentrations were higher (71.6 +/- 19.9 and 52.4 +/- 16.5 nmol/l) than the winter ones (20.4 +/- 6.9 and 21.4 +/- 6.1 nmol/l). Conversely. the winter intact parathyroid hormone (iPTH) serum lev els (4.18 +/- 1.18 and 4.11 +/- 1.35 pmol/l)) were higher than the summer o nes (2.44 +/- 0.82 and 2.71 +/- 0.71 pmol/l). At the two winter time points the 25(OH)D concentrations were lower than 25 nmol/l (10 ng/ml) in 72% (2n d year) and 68% (3rd year) of the adolescents. In the second part of the st udy we tried a vitamin D-3 supplementation procedure designed to maintain t he 25(OH)D and iPTH postsummer serum levels throughout the winter. Pairs of male adolescents matched for height, weight and Tanner pubertal stage were randomly assigned to either vitamin D-3 supplementation (2.5 mg, i.e., 100 000 IU) administered orally at three specific periods (end of September, No vember and January) or no vitamin D-3 treatment (control subjects). Blood w as collected just before the first intake of vitamin D-3 and 2 months after the last intake (March). The control subjects had blood drawn at the same time points. In the vitamin D-3-treated subjects, the concentrations of 25 (OH)D (55.3 +/- 11.5 nmol/l) and of iPTH (3.09 +/- 1.16 pmol/l) in March an d September (53.8 +/- 12.3 nmol/l and 2.75 +/- 1.26 pmol/l) were not signif icantly different. In the control subjects.. March 25(OH)D levels (21.0 nmo l/l were low, with values below 25 nmol/l in 78% of subjects, and iPTH conc entrations (3.97 +/- 1.08 pmol/l) were significantly (p < 0.001) higher tha n in September (2.91 +/- 0.81 pmol/l). The constant vitamin D wintertime de ficiency and wintertime rise in iPTH in adolescent French males throughout puberty has been demonstrated. In adolescents with low dairy calcium intake s, the vitamin D-3 treatment was sufficient to maintain 25(OH)D concentrati ons at their summer levels throughout winter and to prevent an excessive wi nter-time rise in iPTH levels.