Association between intestinal vitamin D receptor, calcium absorption, and serum 1,25 dihydroxyvitamin D in normal young and elderly women.
The exact mechanism for the decrease in intestinal calcium absorption with age is not yet understood. A decrease with age in serum 1,25-dihydroxyvitamin D (1,25(OH)2D) or a decrease in the intestinal vitamin D receptor (VDR) protein concentration are possible causes. The objective of this study was to examine the effect of age on these factors. Fifty-nine young women age 25-35 years were compared with 41 elderly women age 65-83 years who underwent measurements of VDR, calcium absorption using a 20 mg and 100 mg calcium carrier, and calciotropic hormones. Calcium absorption by both tests was lower in the elderly women compared with the young women (p < 0.05). Serum 1,25(OH)2D and duodenal VDR protein concentration were not significantly different between the two age groups. Serum 1,25(OH)2D correlated with the 20 mg calcium absorption test in both young (r = 0.35, p < 0.007) and elderly women (r = 0.58, p < 0.0001) and with the 100 mg calcium absorption in the elderly (r = 0.32; p < 0.05). VDR did not correlate with calcium absorption in young women or elderly women, nor did VDR correlate with serum 1,25(OH)2D and serum 25-hydroxyvitamin D. In summary, the decrease in calcium absorption cannot be explained by a decrease in intestinal VDR. The correlation between serum 1,25(OH)2D and both calcium absorption tests only accounts for 12-30% of the variance in the age-related change in the calcium absorption tests. Other factors, not yet understood, are responsible for the decline in calcium absorption with age.
Kinyamu
H K
HK
Bone Metabolism Unit, Creighton University School of Medicine, Omaha, Nebraska, USA.
Gallagher
J C
JC
Prahl
J M
JM
DeLuca
H F
HF
Petranick
K M
KM
Lanspa
S J
SJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood / Q000378:metabolism*; D002117:Calcitriol / Q000097:blood*; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004386:Duodenum / Q000378:metabolism*; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D018167:Receptors, Calcitriol / Q000378:metabolism*
D002136:Calcium, Dietary; D018167:Receptors, Calcitriol; D002117:Calcitriol