營養物質可能加速或減緩腎臟功能惡化
作者：Jacquelyn K. Beals, PhD
出處：WebMD醫學新聞
November 6, 2009（加州聖地牙哥訊）－麻州波士頓布萊根婦女醫院內科部腎臟科醫師Julie Lin在2009年腎臟週美國腎臟醫學會年度會議上指出，多攝取特定營養素可能對腎臟功能造成影響。
根據護士健康研究的一項分析指出，相較於鈉攝取量四分位數最低者，較高者其腎功能下降的勝算比顯著較高。相對的，貝他胡蘿蔔素攝取四分位數較多的人，相較於攝取最少者，風險下降近40%。
Lin醫師表示，這是另一個不食用高鹽飲食的理由。她在自由交流座談中發表這項發現。
高蛋白飲食被認為會透過超過濾作用（hyoerfultration）加速腎功能惡化，某些研究數據顯示，低蛋白飲食對腎臟功能可能有保護力。然而，對於這個效應的數據，尤其是其他營養素，如果有的話，也是非常少的。她與共同作者Gary Curhan醫師，針對3,296位參加護士健康研究的女性，檢驗個別營養物質與腎臟功能之間的關係。受試者被收納到護士健康研究的腎功能下降或第二型糖尿病的次研究中，研究者在1989年與2000年時記錄參與者的血清肌酐酸和營養物質濃度，根據飲食日記與頻率問卷來估計營養攝取，這些資料追蹤過去一年內超過130種食物與飲料的使用記錄。
在試驗前，年齡中位數為67歲，估計腎絲球廓清率中位數為76 ml/min/1.73 m2，Lin醫師描述這對於該年齡的女性來說算是保養不錯的。
整體而言，主要試驗終點，估計腎絲球廓清率下降超過30%，在11年之間，發生在372位（11.2%）受試者身上。這代表血清肌酐酸濃度平均上升0.33 mg/dl。在校正後，鈉攝取四分位數最高的，相較於最低的，發生主要試驗終點的勝算比為1.52。貝他胡蘿蔔素方面，攝取最多相較於最少者，勝算比為0.62。
Lin醫師報告，其他分析中的營養素與腎臟功能下降並無顯著關係，例如動物脂肪、低脂乳製品、維生素E、葉酸、其他維生素、蛋白質與單元不飽和脂肪酸。
她表示，這項研究大部分收納年齡較大的白人女性，因此，男性、較年輕或是不同種族的人們可能會有不同的結果，即使並沒有生物上的理由顯示為什麼這些發現不能適用於他們身上。
Lin醫師的結論是，整體而言，這些發現代表「飲食上的調整可能是維持腎臟健康的重要策略」。
那什維爾Vanderbilt大學醫學副教授，同時也是大學門診病患透析診所主任的Talat Ikizler醫師表示，腎臟功能與最高的營養物質攝取之間有強烈關聯是非常吸引人的；Ikizler醫師並未參與研究，他提醒這是一項相關性研究，且無法展現出因果關係。除此之外，這代表我們必須花更多的心思在病患的營養需求上。
Lin醫師與Ikizler醫師們表示已無相關資金上的往來。
Nutrients May Slow or Speed Renal Decline
By Jacquelyn K. Beals, PhD
Medscape Medical News
November 6, 2009 (San Diego, California) - High intakes of certain nutrients may have an effect on renal function, Julie Lin, MD, MPH, an internist and nephrologist at Brigham and Women's Hospital in Boston, Massachusetts, said here at Renal Week 2009, the annual meeting of the American Society of Nephrology.
In an analysis of data from the Nurses' Health Study, sodium consumption in the highest quartile was associated with significantly higher odds of renal function decline compared with sodium intake in the lowest quartile. In contrast, beta carotene intake in the highest quartile was associated with a decrease in risk of nearly 40% compared with in the lowest quartile.
"This is another reason not to take a high-salt diet," said Dr. Lin. She presented the findings here during a free communication session.
High-protein diets are thought to hasten progressive renal decline through hyperfiltration, and some data suggest that low-protein diets may protect kidney function. However, data on the effect, if any, of other nutrients on renal function are scarce, Dr. Lin explained. She and her coauthor, Gary Curhan, MD, ScD, examined long-term associations between individual nutrients and kidney function in 3296 women participating in the Nurses' Health Study. The participants were included in the Kidney Function Decline or Type 2 Diabetes Mellitus substudies of the Nurses' Health Study and had had their plasma creatinine and nutrient levels analyzed in 1989 and 2000. Nutrient consumption was estimated from food diaries and frequency questionnaires, which tracked the subjects' consumption of more than 130 foods and beverages during the previous year.
At baseline, median age was 67 years, and median estimated glomerular filtration rate was 76 mL/minute/1.73 m2, which Dr. Lin described as "well-preserved" for women of that age.
Overall, the primary outcome measure- a decrease in estimated glomerular filtration rate of 30% or more - was seen in 372 (11.2%) of the participants during 11 years. This represented a median increase in plasma creatinine of 0.33 mg/dL. After multivariate adjustment, the highest quartile of sodium intake was associated with an odds ratio of 1.52 for the primary outcome compared with the lowest quartile. For beta carotene, the odds ratio was 0.62 for the highest vs the lowest quartile of intake.
No other significant associations were seen for the other nutrients analyzed, such as animal fat, low-fat dairy products, vitamin E, folate, other vitamins, protein, and monounsaturated fat, said Dr. Lin.
This study included mostly older white women, and it is possible that men, younger people, or people of different ethnicities might have different results, although "there's no biological reason why these findings would not apply to them, too," she noted.
Overall, these findings suggest that "dietary modification may represent an important strategy for maintaining kidney health," Dr. Lin concluded.
"The finding of a strong association between kidney function and the highest level of nutrient intake is very interesting," said Talat Ikizler, MD, associate professor of medicine at Vanderbilt University, Nashville, Tennessee, and director of the university's outpatient dialysis clinic. Dr. Ikizler, who was not involved in this research, cautioned that this was an associative study and cannot show cause and effect. Still, he said, "it suggests that we must pay more attention to the nutritional needs of our patients."
Dr. Lin and Dr. Ikizler have disclosed no relevant financial relationships.
Renal Week 2009: American Society of Nephrology (ASN) 2009 Annual Meeting: Abstract SA-FC342. Presented October 31, 2009.
