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Abstract
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 later, at the end of winter (March of 1994). At
each timepoint their height and weight were measured and their pubertal status determined.
Blood was collected and 25-hydroxyvitamin D [25(OH)D], intact parathyroid hormone
(PTH1-84), and 1,25-dihydroxy-vitamin D [1,25(OH)2D] were measured. 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 micrograms/L in September
had significantly (p = 0.0001) fallen by a mean of 23.31 +/- 6.6 micrograms/L in March
(6.61 +/- 2.04 micrograms/L). March and September concentrations of 25(OH)D were significantly
correlated (r = 0.536, p = 0.0039). March values were negatively correlated with the
pubertal status (r = 0.41; p = 0.03). In the meantime, 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)2D
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 positively correlated with pubertal
status (r = 0.49; p = 0.008). Modulation of PTH secretion by vitamin D appears to
be a physiological mechanism occurring during adolescence. In spite of a marked depletion
of vitamin D stores after winter, PTH values remained within normal range. Nevertheless,
we cannot exclude that a more prolonged vitamin D deficiency could adversely affect
bone metabolism during this critical period of life characterized by an increased
need of vitamin D.