AJP - Endocrinology and Metabolism, Vol 270, Issue 3 E483-E490, Copyright © 1996 by American Physiological Society
Effect of aging on the metabolism of phosphorus and 1,25-dihydroxyvitamin D in healthy men
A. A. Portale, B. P. Halloran, R. C. Morris Jr and E. T. Lonergan
Department of Pediatrics, The General Clinical Research Center, University of California, San Francisco 94143, USA.
We tested the hypothesis that aging alters physiological regulation of the
serum concentration of 1,25-dihydroxyvitamin D [1,25(OH)2D] by inorganic
phosphorus. In seven elderly men [age 71 +/- 1 (SE) yr] and 9 young men (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-h 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-h mean serum phosphorus decreased by
0.6 +/- 0.1 mg/dl. Serum concentrations of 1,25(OH)2D varied inversely with
24-h mean serum phosphorus (R= -0.92, P<0.0001). Thus, in healthy
elderly men in whom glomerular filtration rate 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, but 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 regression of serum 1,25(OH)2D on 24-h mean
phosphorus.
