Evidence of an age-related decrease in intestinal responsiveness to vitamin D: Relationship between serum 1,25-dihydroxyvitamin D3 and intestinal vitamin D receptor concentrations in normal women

Peter R. Ebeling, Maria E. Sandgren, Eugene P. Dimagno, Ann W. Lane, Hector F. Deluca, B. Lawrence Riggs

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Abstract

Although aged rats reportedly have reduced intestinal vitamin D receptor (VDR) concentrations, it is unclear whether an analogous age-related defect occurs in man. Thus, we assessed the interrelationship among serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], calcium absorption and intestinal VDR in 44 healthy, ambulatory women, ages 20-87 yr. Fractional calcium absorption was measured after oral administration of 45Ca (20 mg CaCl2 as carrier); serum 1,25-(OH)2D3, by the calf thymus binding assay; and serum intact PTH, by a two-site immunochemiluminometric assay. Vitamin D receptor concentration was measured, by a new immunoradiometric assay, in biopsy specimens taken from the second part of the duodenum during gastroduodenoscopy in 35 of the women. Despite an age-related increase in serum PTH (r = 0.48; P < 0.001) and in serum 1,25-(OH)2D3 concentration (r = 0.32; P < 0.05), intestinal VDR concentration decreased with age (r = -0.38; P = 0.03) and fractional calcium absorption did not change with age. Although a contribution of decreased 25-hydroxyvitamin D 1 α-hydroxylase activity to the blunting of the increase in serum 1,25-(OH)2D3 concentration late in life is not excluded, the data are far more consistent with impaired intestinal responsiveness to 1,25-(OH)2D3 action. This defect could lead to compensatory increases in PTH secretion and 1,25-(OH)2D3 production which maintain calcium absorption and serum ionic calcium, but at the expense of increased bone loss.

Original languageEnglish
Pages (from-to)176-182
Number of pages7
JournalThe Journal of Clinical Endocrinology and Metabolism
Volume75
Issue number1
DOIs
Publication statusPublished - 1 Jan 1992
Externally publishedYes

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