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作者：Nancy A. Melville  
出處：WebMD醫學新聞

　　September 15, 2009 (科羅拉多丹佛) — 研究顯示，攝取鈣質有助於緩解髖骨骨折風險，且與攝取高蛋白質飲食有關，但是，研究者在美國骨骼與礦物質研究協會第31屆年會中發表的一篇新研究認為，鈣的好處可能比瞭解的還要顯著。鈣質補充品可能會因為攝取高蛋白質而可顯著地逆轉骨折風險。
　　
　　一般相信攝取蛋白質可藉由增加鈣質分泌而影響骨骼健康，導致負向鈣平衡。不過，蛋白質也顯示會增加腸道鈣吸收。
　　
　　為了清楚釐清高蛋白質飲食中鈣質的角色，研究者評估了「Framingham Offspring Study」這項研究中，1,752名男性和1,972名女性的資料，他們在1990至1994年或1995至1999年間完成食物頻率問卷。研究者追蹤這些參與者的髖骨骨折，直到2005年。
　　
　　研究者評估研究對象攝取的總蛋白質、熱量、鈣質、維他命D、酒精、咖啡因。根據蛋白質攝取量將研究對象分組，看來源是否為動物性或植物性、動物性與植物性蛋白質比率、攝取的蛋白質總量、校正總攝取熱量。
　　
　　共同作者Shivani Sahni博士向Medscape Ob/Gyn Women's Health表示，我們選擇從不同來源檢視蛋白質攝取，因為研究顯示蛋白質吸收和蛋白質來源有關。
　　
　　結果令人驚訝。低鈣質攝取量(每天<800 mg)者中，攝取動物性蛋白質最高者，髖骨骨折風險是攝取動物性蛋白質最低者的2.84倍。
　　
　　同時，鈣質攝取量每天超過800 mg者中，攝取動物性蛋白質最高的前三分之一，髖骨骨折風險比率比攝取動物性蛋白質最低者低85%。
　　
　　Sahni博士表示，低鈣質攝取量這組中，攝取動物性蛋白質最高的前三分之一，顯然比其他人有較多的骨折。Sahni博士是哈佛醫學院老化研究中心老化與肌肉骨骼研究博士後研究員。
　　
　　她報告指出，截然不同的是，高鈣質攝取量組中，攝取動物性蛋白質最高的前三分之一，髖骨骨折比率顯著低於其他人。這些發現顯示出高蛋白質飲食中鈣質的重要性。Sahni博士結論表示，整體鈣質攝取調整了蛋白質攝取和髖骨骨折風險之間的關係。增加攝取動物性蛋白質可以藉由攝取超過800 mg鈣質發揮作用，但是若鈣質攝取低於800 mg，會有反效果。
　　
　　研究者並未發現整體蛋白質攝取、動物性及植物性蛋白質比率與髖骨骨折風險之間的顯著關係。
　　
　　新墨西哥大學醫學院內科臨床助理教授E. Michael Lewiecki醫師表示，雖然鈣質影響攝取高蛋白質之骨折風險關聯的特定機轉還未確認，該研究提供了飲食中包含這兩種成分之潛在利益的證據。
　　
　　Lewiecki醫師認為，雖然研究結論因為屬於觀察性質而受限，但是適當攝取蛋白質、以及鈣質和維他命D，對於所有人來說都是合理的建議。
　　
　　他指出，這是一個有趣的研究，認為良好的營養對於骨骼健康有好處，各種營養成分之間可能有重要的交互作用。本研究無法解釋蛋白質和鈣質之間交互作用的本質，這是需要後續研究的領域。
　　
　　研究者未接受資金進行本研究。Lewiecki醫師宣告沒有相關財務關係。
　　
　　美國骨骼與礦物質研究協會第31屆年會：摘要1056。發表於2009年9月12日。

Calcium Reverses Fracture Risk Associated With Diet High in Animal Protein

By Nancy A. Melville
Medscape Medical News

September 15, 2009 (Denver, Colorado) — Research has shown that the intake of calcium can help mitigate the increased risk for hip fracture that is associated with the dietary intake of high levels of protein, but a new study suggests that calcium's benefits may even be more significant than realized. Calcium supplements could potentially result in a striking reversal of the fracture risk that comes with high protein intake, investigators announced here at the American Society for Bone and Mineral Research 31st Annual Meeting.

Protein intake is believed to affect bone health by causing an increase in calcium secretion, resulting in a negative calcium balance. However, protein has also been shown to increase intestinal calcium absorption.

To better gauge the role of calcium in a high-protein diet, researchers evaluated data on 1752 men and 1972 women enrolled in the Framingham Offspring Study who completed a food frequency questionnaire either between 1990 and 1994 or from 1995 through 1999. The participants were followed up for hip fracture until 2005.

The researchers estimated the participants' intake of total protein, energy, calcium, vitamin D, alcohol, and caffeine. Participants were grouped by protein intake, whether the source was animal or plant, animal:plant protein ratios, and total protein intake, with adjustments for total energy intake.

"We chose to examine protein intake from different sources because studies have shown that absorption of protein can vary depending on the source of protein," study coauthor Shivani Sahni, PhD, told Medscape Ob/Gyn Women's Health.

The results were striking. Among those who had low calcium intakes (<800 mg per day), the group with the highest intake of animal protein had a risk for hip fracture that was 2.84 times greater than the risk for fracture in the group with the lowest intake of animal protein.

Meanwhile, among those with a higher calcium intake of more than 800 mg per day, the tertile with the highest consumption of animal protein had a rate of hip fracture risk that was in fact 85% lower than the risk in the lowest animal protein intake group.

"In the group with low calcium intake, subjects in the highest tertile of animal protein intake had significantly more fractures compared to the other tertiles," said Dr. Sahni, who is a postdoctoral fellow in aging and musculoskeletal research at the Institute for Aging Research at Harvard Medical School in Boston, Massachusetts.

"Contrastingly, in the group with high calcium, subjects in the highest tertile of animal protein intake had significantly low hip fractures, compared to the rest of the group," she reported. The findings shed important light on the role of calcium intake with a high-protein diet. "Total calcium intake modifies the association of protein intake and the risk of hip fracture," Dr. Sahni concluded. "Increased animal protein intake may be productive with a high calcium intake of 800 mg or more, but the effect may be reversed with an intake of less than 800 mg."

The researchers did not find a significant association between total protein intake and animal:plant protein ratio and the risk for hip fracture.

Although the specific mechanisms behind calcium's apparent ability to offset the fracture risk associated with a high protein intake remain undetermined, the study offers further evidence of potential benefits in combining the 2 in a diet, said E. Michael Lewiecki, MD, clinical assistant professor of medicine at the University of New Mexico School of Medicine, Albuquerque.

"Although the conclusions in this study are limited due to the observational nature of the study, adequate intake of protein, as well as calcium and vitamin D, are probably reasonable recommendations for all," commented Dr. Lewiecki.

"This is an interesting study that suggests that good nutrition is good for skeletal health, and that there may be important interactions among various nutritional factors," he added. "The nature of the interaction between protein and calcium intake is not explained in this report and is an area of interest for future investigation."

The researchers received no funding for the study. Dr. Lewiecki has disclosed no relevant financial relationships.

American Society for Bone and Mineral Research 31st Annual Meeting: Abstract 1056. Presented September 12, 2009.