Calcium absorptive effects of vitamin D and its major metabolites

Robert P. Heaney, M. Janet Barger-Lux, M. Susan Dowell, Tai C. Chen, Michael F. Holick

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162 Scopus citations


The absorptive response to graded doses of vitamin D3, 25(OH)D, and 1,25(OH)2D was measured in healthy adult men after treatment periods of eight, four, and two weeks, respectively. While no relationship was found between baseline absorption and serum vitamin D metabolite levels, all three vitamin D compounds significantly elevated 45Ca absorption from a 300 mg calcium load given as part of a standard test meal. 1,25(OH)2D was active even at the lowest dose (0.5 μg/day), and the slope was such that doubling of absorption would occur at an oral dose of approximately 3 μg/day. 25(OH)D was also active in elevating absorption and did so without raising total 1.25(OH)2D levels. On the basis of the dose response curves for 1.25(OH)2D and 25(OH)D, the two compounds exhibited a molar ratio for physiological potency of approximately 100:1. The absorptive effect of vitamin D3 was seen only at the highest dose level (1250 μg, or 50,000 IU/day) and was apparently mediated by conversion or 25(OH)D. Analysis of the pooled 25(OH)D data from both the 25(OH)D- and vitamin D3-treated groups suggests that approximately one eighth of circulating vitamin D-like absorptive activity under untreated conditions in winter may reside in 25(OH)D. This is a substantially larger share than has been predicted from studies of in vitro receptor binding.

Original languageEnglish (US)
Pages (from-to)4111-4116
Number of pages6
JournalJournal of Clinical Endocrinology and Metabolism
Issue number12
StatePublished - 1997

All Science Journal Classification (ASJC) codes

  • Endocrinology, Diabetes and Metabolism
  • Biochemistry
  • Endocrinology
  • Clinical Biochemistry
  • Biochemistry, medical


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