Background: In experimental studies, a high fluid intake and a corresponding high urine volume have been shown to increase renal excretion rates of urinary free cortisol (UFF) and cortisone (UFE) in adults. We aimed to examine whether 24-h urinary steroid excretion rates are also affected by urine volume in children.
Methods: In 24-h urine samples of 100 prepubertal and 100 pubertal healthy children UFF, UFE, tetrahydrocortisol, 5α-tetrahydrocortisol, and tetrahydrocortisone were quantified by RIA. Urinary dehydroepiandrosterone and its 16α-hydroxylated downstream metabolites (DHEA&M) were analyzed along with the above three glucocorticoid tetrahydrometabolites using GCMS in two additional groups of prepubertal (n=100) and pubertal (n=100) children. The sum of the 3 primarily glucuronidated tetrahydrometabolites (GC3) reflects daily cortisol secretion and DHEA&M represents an index of adrenarchal androgen secretion. Associations of urine volume with outcome variables UFF, UFE, GC3, and DHEA&M were examined in each developmental group using multiple regression models adjusted for sex, body weight, height, and total energy intake.
Results: Significant positive associations were observed between 24-h urine volume and UFF, UFE and DHEA&M in the respective prepupertal and pubertal groups with the highest explained variation for UFE, especially in puberty (R2=0.24). However, GC3 was not significant in any of the groups.
Conclusion: Urinary 24-h excretion rates of UFF, UFE, and DHEA&M, but not glucocorticoid secretion parameters are affected by daily urine volume in healthy free-living children. For a more specific assessment of associations of UFF, UFE, or DHEA&M with (patho)physiologically relevant factors, urine volume should be considered as a confounder.
This work was supported by a grant from European Chemical Industry Council (Cefic).
03 - 07 May 2008
European Society of Endocrinology