Supplements containing soy isoflavones may do little to preserve women's bone mass after menopause.

    In a study of more than 200 women ages 46 to 65, researchers found that the soy supplement did not appear to ward off bone-density loss over 3 years. In general, women on the supplement showed the same degree of bone loss as those given a placebo -- though there was some evidence that a higher dose helped protect bone density in the hip.

    The findings, reported in the American Journal of Clinical Nutrition, add to a conflicting body of research on soy and postmenopausal bone health.

    Some studies have suggested that soy-based foods, isolated soy protein or isoflavone-containing supplements may be beneficial, while others have found no advantage.

    Isoflavones are natural chemicals found in soybeans and certain other plant foods that are structurally similar to estrogen, and may have certain estrogen-like effects in the human body. Since declining estrogen levels after menopause spur bone-density loss, isoflavone supplements could theoretically protect women's bone mass.

    The current findings, however, do not support that theory.

    "I would not be able to recommend that women should take soy isoflavone tablets -- extracted from soy protein -- since these have not been demonstrated convincingly to be effective for prevention of bone loss," lead researcher Dr. D. Lee Alekel, a professor of nutrition at Iowa State University in Ames, told Reuters Health in an email.

    Still, she said, women should still try to eat a variety of soy-based foods -- such as tofu, tempeh and soy-derived versions of cheese and yogurt -- since these are "nutritionally sound" choices.

    For their study, Alekel and her colleagues randomly assigned 255 postmenopausal women to one of three groups: one that took 80 milligrams （mg） of a soy isoflavone supplement each day; one that took a 120-mg dose; and one given inactive placebo pills.

    All of the women also took calcium and vitamin D supplements.

    Over three years, women in the isoflavone and placebo groups showed similar average declines in whole-body bone mass, as well as bone density in the spine and hip area.

    Women in the higher-dose isoflavone group did, however, show less bone loss in the femoral neck -- an area at the top of the thigh bone, where it meets the pelvis. But, the researchers write, because the effect was "very modest," and limited to the femoral neck, "we cannot conclude that soy isoflavones hold potential promise in the prevention of postmenopausal osteoporosis."

    The idea that soy or soy isoflavones may protect bone mass comes, in part, from studies showing lower rates of hip fracture among women in Southeast Asia, where the traditional diet is rich in soy.

    Those types of studies do not prove cause-and-effect, however. Because the current study looked only at soy isoflavone supplements, Alekel said it cannot speak to the potential effects of soy foods on women's bone health.

    含有大豆黃酮異構衍生物的補充品對防止女性絕經后的骨質流失幾乎沒有作用。

    在一項對200多名年齡在46到65歲的女性調查研究中，研究者發現，在這3年當中大豆補充品并沒有防止骨密度的減少。雖然有些證據表明大劑量的補充品有助于保持髖部的骨密度，但是從總體上看，給予這種補充物的女性與給予安慰劑的女性其骨質流失程度是一致的。

    發表在美國臨床營養雜志的這項發現，是對大豆與絕經后骨健康研究的一個反例補充。

    一些研究提示，大豆食品、分離出的大豆蛋白或是黃酮異構體衍生物的補充品可能對人體有益，然而另一些研究卻沒有發現對人體有益。

    黃酮異構體衍生物是存在于大豆和其他某種植物食物中的天然化學成分。其結構上與雌激素相似，并且對人體可能有一定的雌激素樣作用。由于絕經后雌激素水平下降導致了骨密度的降低，理論上，含有黃酮異構體衍生物的補充品就可能保持女性的骨質重量。

    然而目前的發現還不支持上述理論。

    "我不能給出建議說，女性應該服用含有從大豆蛋白中提取的黃酮異構衍生物的片劑，因為還沒有明確這些衍生物對預防骨質流失是有效的，"重要研究成員D.Lee Alekel博士（愛荷華州立大學營養學教授）在給路透社健康專欄的一封e-mail里這樣寫道。

    但是她說，女性朋友們應該依然試著食用各種大豆制品的食物，例如豆腐、印尼豆豉以及各種來源于大豆的奶酪和酸奶。這些都是"天然的極佳"選擇。

    為了研究，Alekel和她的同事隨機分配255名絕經后婦女到三個實驗組中。一組每天服用80毫克的含有大豆黃酮異構體衍生物的補充品，一組每天服用120毫克，剩下一組給予沒有作用效果的安慰劑。

    這些婦女同時也全部服用鈣劑和維生素D.

    三年后，黃酮異構體衍生物實驗組和安慰劑組的女性，其全身骨質重量平均下降水平相似，同樣，脊椎和髖部的骨密度平均下降水平也相似。

    不過，服用高劑量黃酮異構體衍生物組的女性，其股骨頸（大腿骨頂端位置，連接骨盆）骨質流失量要比其他組少。研究人員報告說，由于效果"很溫和",且只對股骨頸有效，"我們不能作出大豆黃酮異構體衍生物對預防絕經后的骨質疏松癥有潛在前景的結論。"

    在某種程度上，大豆或大豆黃酮異構體衍生物有可能維護骨質增加的研究觀點顯示，東南亞的女性髖部骨折發生率較低。這些地方的傳統飲食富含大豆。

    然而那些各種類型的研究沒能驗證因果關系。因為目前的研究只關注于大豆黃酮異構體衍生物補充品，Alekel說這不能證明大豆食品對女性骨質健康有潛在效用。