Bioavailability of calcium salts and the effects of soy isoflavones on calcium and bone metabolism in adult ovariectomized rats
Abstract
Osteoporosis is a disease resulting from bone loss and from the structural deterioration of bone tissue. Yet osteoporosis is both controllable and preventable. In terms of prevention, a good source of calcium supplementation is important in promoting strong, healthy bones. The bioavailability of calcium ascorbate and calcium acetate was studied in an animal model using a radioactive tracer technique. At two dosage levels, calcium from calcium ascorbate was absorbed higher than from calcium acetate, indicating calcium ascorbate is a better bioavailable calcium supplement. Alpha-lactalbumin, a whey protein fraction, further enhanced calcium absorption from both salts in an animal model. Therefore, calcium ascorbate in combination with alpha-lactalbumin was a superior bioavailable calcium source. Several animal and short-term human studies indicate that isoflavones may be used as an alternative therapy to estrogen replacement therapy. However, the results were contradictory. The inadequacy of information and controversy on skeletal effects of isoflavones led us to design the present study to test the effectiveness of soy isoflavones on treating osteoporosis in comparison to the estrogen replacement therapy in an adult animal model for postmenopausal osteoporosis. Unmated 6 mo. old ovariectomized and sham operated female Sprague-Dawley rats were randomly assigned to 9 groups (16 rats/group). Calcium metabolic balance, bone densitometry, bone histomorphometry and bone mechanical testing were used to investigate calcium and bone metabolism. After ovariectomy, estrogen prevented bone loss in trabecular bone and suppressed formation on both trabecular and cortical bone surfaces. Isoflavones given as soy protein or supplements did not prevent trabecular bone loss. Combining isoflavones with estrogen had no additional benefits. None of the treatments affected calcium absorption or calcium balance significantly. Therefore, we conclude that soy isoflavones did not alter calcium metabolism or bone metabolism at the doses tested.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition|Food science|Surgery
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