飲食中的亞麻油酸可能與潰瘍性結腸炎有關

作者：Laurie Barclay, MD  
出處：WebMD醫學新聞

　　July 24, 2009 — 一項7月23日線上發表於腸胃醫學期刊的研究顯示，飲食中的亞麻油酸可能與潰瘍性結腸炎有關；這是一項前瞻性世代研究中的巢式病例對照（nested case-control）分析。
　　
　　來自英國諾威治東安吉利亞大學的A. Hart醫師與其歐洲前瞻性癌症與營養（EPIC）研究的同事們寫到，飲食中的亞麻油酸(一種n-6多元不飽和脂肪酸)會被代謝成花生四烯酸，這是一種大腸細胞細胞膜的成分。花生四烯酸的代謝物具有促進發炎性質，且在罹患潰瘍性結腸炎病患粘膜中是增加的。這項研究的主要目的是進行第一個研究飲食中亞麻油酸是否會增加罹患潰瘍性結腸炎風險的研究。
　　
　　在EPIC研究中，203,193位女性以完成飲食頻率問卷來提供飲食相關資料。受試者們居住瑞典、英國、丹麥、德國或是義大利，年齡介於30至74歲。追蹤受試者是否有發生非遺傳性潰瘍性結腸炎，且每位罹患潰瘍性直腸炎病患都與4位控制組病患比較。在校正性別、年齡、是否吸菸、總能量攝取、以及研究中心，以亞麻油酸攝取四分位數計算罹患潰瘍性直腸炎風險。
　　
　　在平均後續追蹤4.0年（範圍介於1.7-11.3歲）間，126位受試者發生潰瘍性結腸炎，其中47%是女性。診斷時平均年齡為60歲。亞麻油酸攝取量最高的前四分之一病患罹患潰瘍性結腸炎風險最高（勝算比[OR]為2.49；95%信賴區間[CI]為1.23-5.07；P=0.01）。四分位數組別之間差異的趨勢達統計上顯著水準（每增加一四分位數OR增加1.32；95% CI為1.04-1.66；趨勢P值為0.02）。
　　
　　研究作者們寫到，這項研究數據支持飲食中亞麻油酸與潰瘍性結腸炎的病理生成是有關的。據估計30%的病例可以歸因為飲食攝取量高於亞麻油酸攝取量最低的四分位數。
　　
　　相對的，攝取發現自鮭魚與鯡魚的二十二碳六烯酸（omega-3酸），攝取最多的受試者，發生潰瘍性結腸炎的風險下降77%。
　　
　　這項研究的限制包括僅在收納時取得是否吸菸的資料，而在後續追蹤時並沒有相關資料、以飲食頻率問卷量測的誤差、以及因為受試者主要是中老年族群患者而限制其普遍性。
　　
　　研究作者的結論是，潰瘍性結腸炎患者調整飲食並無好處，雖然，根據這項研究發現，飲食中亞麻油酸含量較低可能值得進一步的研究。因為看似合理的生物機轉與來自流行病學研究的證據支持，這之間的正面關係可能反映了因果關係。這之間的關係，需要在其他不同族群的病理生成研究中進一步確認其一致性。
　　
　　Sir Halley Stewart信託、國家結腸炎與克隆氏症協會以及國家健康服務部門東區分部贊助這項分析。EPIC研究由英國癌症與醫學研究局；瑞典癌症學會；瑞典研究局；斯堪那區；丹麥癌症學會；Stiftung Landesbank Baden-W?rttemberg；歐盟；德國癌症援助協會；聯邦研究與科技部；以及Associazione Italiana per la Ricerca contro il Cancro and Regione Toscana贊助這項研究。研究作者們表示沒有相關資金上的往來。

Dietary Linoleic Acid May Be Implicated in Ulcerative Colitis

By Laurie Barclay, MD
Medscape Medical News

July 24, 2009 — Dietary linoleic acid may be implicated in ulcerative colitis, according to the results of a nested case–control study within a prospective cohort study reported online July 23 in Gut. Linoleic acid occurs naturally in red meat, various cooking oils, and some margarines.

"Dietary linoleic acid, an n-6 polyunsaturated fatty acid, is metabolised to arachidonic acid, a component of colonocyte membranes," write A. Hart, MD, from the University of East Anglia in Norwich, United Kingdom, and colleagues from the Inflammatory Bowel Disease in European Prospective Investigation into Cancer and Nutrition (EPIC) Study. "Metabolites of arachidonic acid have pro-inflammatory properties and are increased in the mucosa of patients with ulcerative colitis. The aim of this investigation was to conduct the first prospective cohort study investigating if a high dietary intake of linoleic acid increases the risk of developing incident ulcerative colitis."

Within the EPIC study, 203,193 men and women provided dietary data by completing food frequency questionnaires. Participants were 30 to 74 years of age and residents of the United Kingdom, Sweden, Denmark, Germany, or Italy. Participants were followed up for development of incident ulcerative colitis, and each patient with ulcerative colitis was matched with 4 control patients. After adjustment for sex, age, smoking, total energy intake, and study center, the risk for ulcerative colitis was calculated by quartile of linoleic acid intake.

After a median follow-up of 4.0 years (range, 1.7 – 11.3 years), 126 participants developed ulcerative colitis, of whom 47% were women. Average age at diagnosis was 60 years. Risk for ulcerative colitis was increased for the highest quartile of linoleic acid intake (odds ratio [OR], 2.49; 95% confidence interval [CI], 1.23 – 5.07; P = .01). There was a significant trend across quartiles (OR, 1.32 per quartile increase; 95% CI, 1.04 – 1.66; P = .02 for trend).

"The data support a role for dietary linoleic acid in the aetiology of ulcerative colitis," the study authors write. "An estimated 30% of cases could be attributed to having dietary intakes higher than the lowest quartile of linoleic acid intake."

In contrast, the highest intake of the omega-3 fatty acid docosahexanoic acid, which is found in salmon and herring, was associated with a 77% decrease in risk of developing ulcerative colitis.

Limitations of this study include that smoking data were available only at recruitment and not during subsequent follow-up, measurement error in the food frequency questionnaire, and limited generalizability because of a predominantly middle-aged to elderly population.

"There are no dietary modifications of benefit in patients with ulcerative colitis, although, based on this study's findings, a diet low in linoleic acid may merit investigation," the study authors conclude. "The positive association may reflect a causal association because of both a plausible biological mechanism and supportive evidence from other epidemiological studies. The association needs to be further investigated in other aetiological work in different populations to assess consistency."

The Sir Halley Stewart Trust, the National Association for Colitis and Crohn's Disease, and the National Health Service Executive Eastern Region funded this analysis. EPIC is supported by Cancer Research UK and the Medical Research Council, UK; the Swedish Cancer Society; the Swedish Research Council; the Region of Skane; the Danish Cancer Society; "Stiftung Landesbank Baden-Wurttemberg"; the European Union; Deutsche Krebshilfe; the Federal Ministry of Research and Technology; and the Associazione Italiana per la Ricerca contro il Cancro and Regione Toscana. The study authors have disclosed no relevant financial relationships.

Gut. Published online July 23, 2009.