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作者：Nancy A. Melville  
出處：WebMD醫學新聞

　　September 24, 2009 (科羅拉多丹佛) — 美國骨質研究協會第31屆年會中發表的研究，對多攝取異黃酮有助於停經相關骨質流失的理論提出質疑。
　　
　　因為「Women's Health Initiative」這項研究發現雌激素及黃體素治療與乳癌及心血管併發症有關，荷爾蒙替代療法就失寵了！有些婦女轉而相信富含異黃酮的大豆有助於預防或延緩停經相關的骨質流失。
　　
　　這兩篇研究結果並不支持此一理論。
　　
　　第一篇包括248名停經婦女、平均年紀52.5歲；66%是西班牙裔且研究開始時沒有人有骨質疏鬆。研究者隨機平均分派這些婦女接受每天200 mg的大豆異黃酮或安慰劑，為期兩年。
　　
　　整個研究期間，研究者觀察發現，在大豆組與安慰劑組，第一型骨膠原蛋白之氮端端肽值不變。研究者結論表示，純化的大豆異黃酮無法影響停經後最初五年之婦女的骨骼再吸收。
　　
　　研究者表示，他們計畫進行後續研究，以評估大豆異黃酮預防停經後骨質流失與停經症候群的效果。
　　
　　第二篇研究是隨機雙盲試驗，比較每天80 mg或120 mg大豆異黃酮錠劑與安慰劑的效果，研究對象是45至65歲的停經後婦女。每一組的婦女也接受每天500 mg鈣質與600 IU的維他命D3。
　　
　　完成三年研究的209名研究對象中，研究者發現，三組的腰椎、髖骨或全身骨密度值沒有顯著差異；不過，120 mg劑量對於股骨頸BMD顯示有顯著的保護效果(P= .024)。大豆之外的其他因素，例如年紀、全身體脂肪量、第一型膠原蛋白之交聯C端端肽，是這些研究對象骨骼結果的共通預測因子。
　　
　　大豆異黃酮治療與副作用無關。在三年研究期間，子宮內膜厚度減少，血清25(OH)維他命D值增加，骨骼代謝周轉生化標記並未改變。
　　
　　第一作者、愛荷華州立大學營養與健康研究中心營養學教授D. Lee Alekel博士表示，研究發現與研究者原本假設的大豆異黃酮有潛在利益相反，而且，在骨骼結果的其他預測因子中，對於股骨頸BMD的適度保護效果，並不具有足以提出其他建議的強力證據。
　　
　　她表示，我們假設異黃酮錠劑可以保留BMD，而生物學(年紀、體重、血清25(OH)維他命D值)與生活型態(體力活動與飲食)等因素則是管控BMD流失。
　　
　　校正這些因素之後，120 mg劑量對於股骨頸BMD顯示有保護效果(P= .024)。不過，比較全身體脂肪量或年紀時，較高的劑量對於股骨頸的影響效果很小。
　　
　　Alekel博士指出，之前的研究也已經否認大豆異黃酮保護骨骼的好處。
　　
　　她表示，除了我們的研究結果，其他檢視大豆異黃酮錠保護骨骼停經後婦女之骨骼的研究顯示，對於骨密度效果小。
　　
　　Alekel博士指出，骨質疏鬆風險中值得注意的部位是腰椎與近端股骨(髖骨)，而非全身骨骼。充其量，只有一些研究指出一點骨骼保留效果，而多數設計良好的研究都顯示只有一點生物反應。
　　
　　波特蘭Maine醫學中心研究機構資深科學家Clifford J. Rosen醫師同意，該研究增加了質疑大豆異黃酮保護停經者骨質流失之治療利益的疑問。
　　
　　他表示，隨機試驗提供有力證據認為，大豆或異黃酮對於骨骼代謝周轉的效果有限，Alekel博士研究所見的大豆對於股骨頸的效果，可能無法改變此一結論。股骨量的些微效果可能無臨床顯著意義。
　　
　　兩篇研究都接受國家關節炎與肌肉骨骼和皮膚疾病研究中心的支持。 Alekel博士和Rosen醫師皆宣告沒有相關財務關係。
　　
　　美國骨質研究協會(ASBMR)第31屆年會：摘要SA0412與MO0374。發表於2009年9月11-15日。

Soy Isoflavone Tablets Do Not Appear to Prevent Menopausal Bone Loss

By Nancy A. Melville
Medscape Medical News

September 24, 2009 (Denver, Colorado) — Studies presented here at the American Society for Bone and Mineral Research 31st Annual Meeting cast doubt on the theory that a high isoflavone intake could help slow bone loss related to menopause.

With hormone replacement therapy falling out of favor after findings from the Women's Health Initiative linked estrogen and progestin therapies to breast cancer and cardiovascular complications, some women turned to soy in the belief that its high isoflavone content could help prevent or slow menopause-related bone loss.

Findings from 2 studies presented here do not support that theory.

The first involved 248 menopausal women with a mean age of 52.5 years; 66% were Hispanic and none had osteoporosis at baseline. The researchers randomized the women in equal proportions to receive either soy isoflavone 200?mg daily or placebo over the course of 2 years.

Throughout the study, the researchers observed that N-telopeptide of type?I bone collagen levels remained constant for both the soy and placebo groups. The researchers concluded that "purified soy isoflavones do not influence bone resorption in women in the first 5 years of menopause."

The researchers say they plan future studies to assess the effectiveness of soy isoflavones in preventing postmenopausal bone loss and menopausal symptoms.

The second study was a randomized double-blind trial comparing the effects of 80?mg or 120?mg daily soy isoflavone tablets or matching placebo in 3 groups of postmenopausal women between the ages of 45 and 65 years. The women in each group also received daily calcium 500?mg and daily vitamin D3 600?IU.

Among the 209 subjects who completed the 3-year study, the researchers found no significant differences in lumbar spine, hip, or whole-body bone mineral density (BMD) among the 3 groups; however, the 120?mg dose did show a significant protective effect on femoral neck BMD (P?= .024). Factors other than soy, including age, whole-body fat mass, and cross-linked C-terminal telopeptides of type?I collagen, were found to be common predictors for bone outcome among the subjects.

Soy isoflavone treatment was not associated with adverse events. Over the 3-year study period, endometrial thickness declined, serum 25(OH) vitamin?D levels increased, and biochemical markers of bone turnover did not change.

Lead author D. Lee Alekel, PhD, professor of nutrition at Iowa State University's Nutrition and Wellness Research Center in Ames, said the findings countered the researchers' original hypothesis about potential benefits from soy isoflavone, and, in the context of the other predictors of bone outcome, the modest protection seen in femoral neck BMD did not qualify as strong enough evidence to suggest otherwise.

"We hypothesized that isoflavone tablets would spare BMD, with biologic [age, body weight, serum 25(OH) vitamin?D] and lifestyle [physical activity, dietary intake] factors modulating BMD loss," she said.

"[After] adjusting for these factors, the 120?mg [dose] was protective (P?= .024) for femoral neck BMD. However, in comparison with whole-body fat mass or age, the higher-dose treatment exerted minimal effect on the femoral neck."

Dr. Alekel noted that previous studies have also negated benefits from soy isoflavone tablets on bone protection.

"Aside from the results of our study, other studies examining the effect of soy isoflavone tablets on bone for postmenopausal women have demonstrated little effect on bone mineral density," she said.

"The bone sites of interest for osteoporotic risk should be the lumbar spine and proximal femur (hip) rather than whole-body bone. At best, some studies have indicated a small bone-sparing effect, while most well-conducted studies have shown little biological response," Dr. Alekel noted.

Clifford J. Rosen, MD, senior scientist at Maine Medical Center's Research Institute in Portland, agreed that the studies add to a growing body of research that cast doubt on any therapeutic benefits of soy isoflavones in preventing menopausal bone loss.

"Randomized trials provide strong evidence that there is little effect of soy or isoflavones on bone turnover," he said, adding that the effect of soy on the femoral neck seen in Dr. Alekel's study likely doesn't change that conclusion. "The very modest effects on femoral bone mass are probably not clinically significant."

Both studies received support from the National Institute of Arthritis & Musculoskeletal & Skin Diseases, NIH. Drs. Alekel and Rosen have disclosed no relevant financial relationships.

American Society for Bone and Mineral Research (ASBMR) 31st Annual Meeting: Abstracts SA0412 and MO0374. Presented September 11-15, 2009.