Our group is interested in evaluating early effects of dietary interventions on bone loss. Postmenopausal women lose bone following reduction in estrogen which leads to increased risk of fracture. Traditional means of monitoring bone loss and effectiveness of treatments include changes in bone densitometry which takes years to observe effects and changes in biochemical markers of bone turnover which are highly variable and lack specificity. Prelabeling bone with 41Ca and measuring urinary 41Ca excretion with Accelerator Mass Spectrometry provides a sensitive, specific and rapid approach to evaluating effectiveness of treatment.
Estrogen therapy was a mainstay in the treatment of postmenopausal bone loss until the Women's Health Initiative demonstrated that estrogen plus progesterone increased risk of breast cancer and other undesirable side effects. Dietary supplements, especially phytoestrogens, have been the focus of recent interest as an alternative to estrogen therapy. We evaluated the dose response of soy isoflavones in a soy protein powder on bone resorption on 13 postmenopausal women with 41Ca technology. Following Ан 100 days post dose with 41Ca, women were fed 40 grams soy protein containing 0,97.5 or 135.5 mg isoflavones /day in a randomized order. Each treatment period of 50 days was followed by a 50 day recovery period. Soy protein with isoflavones up to 135.5 mg/day had no effect on bone resorption as assessed by urinary 41Ca excretion and traditional biochemical markers of bone turnover. One subject left the study when her physician put her on estrogen therapy. Subsequently, her urinary 41Ca levels dropped. We estimate that this intervention can reduce urinary 41Ca output by 15-25%. This demonstrated the potential of this method to show a treatment effect.
To better understand 41Ca technology as a tool for measuring effective treatments on reducing bone resorption, we have compared 3H-tetracycline (3H-TC) and calcium metabolism under various conditions in rat models. 3H-TC is thought to exclusively represent bone resorption, whereas, urinary calcium labels may reflect net turnover since some label released from bone can be reincorporated into bone. These studies have shown that bone resorption determined from 3H-TC or calcium tracers is similar although kinetics of excretion differs. Dietary interventions, such as Ca level, may show transcient effects on bone resorption, at least in the rat model.
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See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)