VITAMIN-D-DEPENDENT SEASONAL-VARIATION OF PTH IN GROWING MALE-ADOLESCENTS

Twenty-eight young male adolescents (age from 13 years 6 months to 15 years 9 months) from a horseback-riding school were studied, They were studied at the end of summer (September of 1993) and, six months late r, at the end of winter (March of 1994), At each timepoint their heigh t and weight were measured and their pubertal status determined, Blood was collected and 25-hydroxyvitamin D [25(OH)D], intact parathyroid h ormone (PTH1-84), and 1,25-dihydroxyvitamin D [1,25(OH)(2)D] were meas ured. After winter, weight and height had increased by a mean of 2.9 /- 1.3 kg and of 3.3 +/- 1.2 cm, respectively. 25(OH)D concentrations which were 29.96 +/- 7.46 mu g/L in September had significantly (p = 0 .0001) fallen by a mean of 23.31 +/- 6.6 mu g/L in March (6.61 +/- 2.0 4 mu g/L). March and September concentrations of 25(OH)D were signific antly correlated (r = 0.536, p = 0.0039), March values were negatively correlated with the pubertal status (r = 0.41; p = 0.03), In the mean time, PTH had significantly (p = 0.0001) increased by a mean of 8.59 /- 8.53 ng/L (22.8 +/- 7.44 ng/L in September vs, 30.33 +/- 8.05 ng/L in March), A statistically significant correlation between PTH and 25( OH)D concentrations (r = 0.493; p 0.0001) was obtained. Serum 1,25(OH) (2)D concentrations measured in September (37.7 +/- 12.94 ng/L) and in March (38.2 +/- 7.8 ng/L) were not different, March values were posit ively correlated with pubertal status (r = 0.49; p = 0.008). Modulatio n of PTH secretion by vitamin D appears to be a physiological mechanis m occurring during adolescence, In spite of a marked depletion of vita min D stores after winter, PTH values remained within normal range, Ne vertheless, we cannot exclude that a more prolonged vitamin D deficien cy could adversely affect bone metabolism during this critical period of life characterized by an increased need of vitamin D.