Effect of aging on the metabolism of phosphorus and 1, 25
-dihydroxyvitamin d in healthy men.
Portale, Anthony A., Bernard P. Halloran, R. Curtis Morris, Jr., and
Edmund T. Lonergan.
Departments of Pediatrics and Medicine, The General Clinical
Research Center, University of California and Veterans Affairs
Medical Center, San Francisco, CA. 94143
APStracts 2:0243E, 1995.
We tested the hypothesis that aging alters physiologic regulation of
the serum concentration of 1,25(OH)2D by inorganic phosphorus. In 7
elderly men (age 71 +/- 1 SEM yr) and 9 young (29 +/- 2 yr), dietary
phosphorus was first normal, then increased and decreased within its
normal range. At each intake of phosphorus, serum concentrations of
1,25(OH)2D in the elderly did not differ from those in young men, but
fasting and 24-hr mean serum concentrations of phosphorus were lower
in elderly men. With phosphorus restriction, in each group serum
1,25(OH)2D increased by 47%, and 24-hr mean serum phosphorus
decreased by 0.6 +/- 0.1 mg/dl. Serum concentrations of 1,25(OH)2D
varied inversely with 24-hr mean serum phosphorus (R = -0.92,
P<0.0001). Thus, in healthy elderly men in whom GFR is normal or
near normal, serum concentrations of 1,25(OH)2D increase when dietary
phosphorus is restricted; the magnitude of response at steady-state
is unaffected by aging, however the time course of response is
delayed. At any level of serum phosphorus, serum 1,25(OH)2D is lower
than that in young men, as reflected by a lower intercept of the
regression of serum 1,25(OH)2D on 24-hr mean phosphorus.
Received 30 May 1995; accepted in final form 20 October 1995.
APS Manuscript Number E240-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95