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ORIGINAL RESEARCH ARTICLE

Calcium Bioavailability and Kinetics of Calcium Ascorbate and Calcium Acetate in Rats

Jianwei Cai^*,2, Qinmin Zhang^*,3, Meryl E. Wastney and Connie M. Weaver^*,1

^* Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47907; and Metabolic Modeling Sciences, Ltd., Hamilton, New Zealand

To whom requests for reprints should be addressed at ¹ Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47906. E-mail: weavercm{at}cfs.purdue.edu

The objective was to investigate the bioavailability and mechanism of calcium absorption of calcium ascorbate (ASC) and calcium acetate (AC). A series of studies was performed in adult Sprague-Dawley male rats. In the first study, each group of rats (n = 10/group) was assigned to one of the five test meals labeled with ⁴⁵Ca: (i) 25 mg calcium as heated ASC or (ii) unheated ASC, (iii) 25 mg calcium as unheated AC, (iv) 3.6 mg Ca as unheated ASC, or (v) unheated AC. Femur uptake indicated better calcium bioavailability from ASC than AC at both calcium loads. A 5-min heat treatment partly reduced bioavailability of ASC. Kinetic studies were performed to further investigate the mechanism of superior calcium bioavailability from ASC. Two groups of rats (n = 10/group) received oral doses of 25 mg Ca as ASC or AC. Each dose contained 20 µCi ⁴⁵Ca. Two additional groups of rats (n = 10/group) received an intravenous injection (iv) of 10 µCi ⁴⁵Ca after receiving an unlabeled oral dose of 25 mg calcium as ASC or AC. Sequential blood samples were collected over 48 hrs. Urine and fecal samples were collected every 12 hrs for 48 hrs and were analyzed for total calcium and ⁴⁵Ca content. Total calcium and ⁴⁵Ca from serum, urine, and feces were fitted by a compartment kinetics model with saturable and nonsaturable absorption pathways by WinSAAM (Windows-based Simulation Analysis and Modeling). The difference in calcium bioavailability between the two salts was due to differences in saturable rather than passive intestinal absorption and not to endogenous secretion or calcium deposition rate. The higher bioavailability of calcium ascorbate was due to a longer transit time in the small intestine compared with ASC.

Key Words: calcium • ascorbate • bioavailability • acetate • kinetics

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