深海魚油吃了無用也無害嗎

Fish oil is now the third most widely used dietary supplement in the United States, after vitamins and minerals, according to a recent report from the National Institutes of Health. At least 10 percent of Americans take fish oil regularly, most believing that the omega-3 fatty acids in the supplements will protect their cardiovascular health.

最近，一份來自美國國立衛生研究院(National Institutes of Health)的報告稱，在美國應用最廣泛的若干膳食補充劑中，魚油位列第三，僅次於維生素和礦質元素。至少10%的美國人定期服用魚油，其中大多數人都相信魚油中的ω-3脂肪酸會促進心血管健康。

But there is one big problem: The vast majority of clinical trials involving fish oil have found no evidence that it lowers the risk of heart attack and stroke.

不過一個明顯的問題是：絕大多數有關魚油的臨牀試驗都未發現任何證據足以證明魚油的確可以降低心肌梗死和中風的風險。

From 2005 to 2012, at least two dozen rigorous studies of fish oil were published in leading medical journals, most of which looked at whether fish oil could prevent cardiovascular events in high-risk populations. These were people who had a history of heart disease or strong risk factors for it, like high cholesterol, hypertension or Type 2 diabetes.

2005年至2012年，頂尖醫學期刊上至少登載了二十多篇有關魚油的嚴謹研究，其中大部分研究都探討了魚油能否預防高危人羣患心血管疾病的問題。這裏的高危人羣是指：具有心臟病史或者具有強風險因素，如高膽固醇、高血壓或患2型糖尿病的病人。

All but two of these studies found that compared with a placebo, fish oil showed no benefit.

這些研究中，除了兩項外研究，其他所有研究都發現與安慰劑相比，魚油未顯示任何效果。

And yet during this time, sales of fish oil more than doubled, not just in the United States but worldwide, said Andrew Grey, an associate professor of medicine at the University of Auckland in New Zealand and the author of a 2014 study on fish oil in JAMA Internal Medicine.

然而，在此期間，不只美國，全球的魚油銷售量都翻了一倍以上，2014年在《美國醫學會期刊：內科學》雜誌上(JAMA Internal Medicine)發表了一項研究的作者，新西蘭的奧克蘭大學(University of Auckland)的醫學副教授安德魯·格雷(Andrew Grey)說道。

“There’s a major disconnect,” Dr. Grey said. “The sales are going up despite the progressive accumulation of trials that show no effect.”

“脫節相當嚴重，”格雷博士說。“儘管越來越多的試驗都證明（魚油）無效，但其銷售量在節節攀升。”

In theory at least, there are good reasons that fish oil should improve cardiovascular health. Most fish oil supplements are rich in two omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — that can have a blood-thinning effect, much like aspirin, that may reduce the likelihood of clots. Omega-3s can also reduce inflammation, which plays a role in atherosclerosis. And the Food and Drug Administration has approved at least three prescription types of fish oil — Vascepa, Lovaza and a generic form — for the treatment of very high triglycerides, a risk factor for heart disease.

至少在理論上，有很多理由使人覺得魚油應該可以改善心血管健康。大多數魚油補充劑都富含兩種ω-3脂肪酸——二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)，這兩種物質都像阿司匹林那樣對血液有稀釋效果，從而降低發生血栓的可能性。ω-3脂肪酸還可以減少炎症，而炎症在動脈粥樣硬化中有一定的作用。美國食品和藥品監督管理局(Food and Drug Administration)現已批准了至少三種魚油產品——Vascepa、Lovaza（ω-3脂肪酸乙酯膠囊）和一種仿製藥——作爲治療甘油三酯過高（心臟病的一個風險因素）的處方藥。

But these properties of omega-3 fatty acids have not translated into notable benefits in most large clinical trials.

但在大多數大型臨牀試驗中，脂肪酸的這些特性未能轉化爲顯著的效益。

Some of the earliest enthusiasm for fish oil goes back to research carried out in the 1970s by the Danish scientists Dr. Hans Olaf Bang and Dr. Jorn Dyerberg, who determined that Inuits living in northern Greenland had remarkably low rates of cardiovascular disease, which they attributed to an omega-3-rich diet consisting mainly of fish, seal and whale blubber. Dr. George Fodor, a cardiologist at the University of Ottawa, outlined flaws in much of this early research, and he concluded that the rate of heart disease among the Inuit was vastly underestimated. But the halo effect around fish oils persists.

對魚油最早的追捧可以追溯到丹麥科學家漢斯·奧拉夫·邦(Hans Olaf Bang)博士和約恩·戴爾伯格(Jorn Dyerberg)博士在20世紀70年代進行的一項研究。他們認爲生活在格陵蘭北部的因紐特人患心血管疾病比率非常低的原因是，因紐特人的膳食以魚類、海豹和鯨脂爲主，這些食品富含ω-3脂肪酸。渥太華大學(University of Ottawa)的心臟病專家喬治·福多爾(George Fodor)博士列舉了這一研究中的諸多破綻，並斷定因紐特人中的心臟病率被大大低估了。不過，縈繞在魚油之上的光環仍然閃耀不息。

The case for fish oil was bolstered by several studies from the 1990s, including an Italian study that found that heart attack survivors who were treated with a gram of fish oil daily had a drop in mortality, compared with patients taking vitamin E. These findings prompted groups like the American Heart Association to endorse fish oil about a decade ago as a way for heart patients to get more omega-3s in their diets.

該項關於魚油的研究得到了從20世紀90年代起的若干項研究的支持，其中一項來自意大利的研究發現，每日服用一克魚油的心肌梗死倖存者的死亡率較服用維生素E的患者有所降低。這些研究結果促使美國心臟協會(American Heart Association)等組織在大約十年前大力推崇心臟病患者服用魚油來補充膳食ω-3脂肪酸。

“But since then, there has been a spate of studies showing no benefit,” said Dr. James Stein, the director of preventive cardiology at University of Wisconsin Hospital and Clinics. Among them was a clinical trial of 12,000 people, published in The New England Journal of Medicine in 2013, that found that a gram of fish oil daily did not reduce the rate of death from heart attacks and strokes in people with evidence of atherosclerosis.

“但此後的大量研究卻顯示魚油沒什麼功效，”威斯康星大學醫院和診所(University of Wisconsin Hospital and Clinics)的預防心臟病學主任詹姆斯·斯坦(James Stein)博士說。其中2013年發表在《新英格蘭醫學雜誌》(The New England Journal of Medicine)上的一項涉及12000人的臨牀試驗發現，在存在動脈粥樣硬化證據的人羣中，每日服用一克魚油並未降低因心肌梗死和中風死亡率。

“I think that the era of fish oil as medication could be considered over now,” said the study’s lead author, Dr. Gianni Tognoni of the Institute for Pharmacological Research in Milan.

該研究的作者之一，米蘭藥理研究所(Institute for Pharmacological Research in Milan)的詹尼·託尼奧尼(Gianni Tognoni)博士說：“我認爲，現在是該考慮結束將魚油當做藥物的時代了。”

Dr. Stein said the early fish oil studies took place in an era when cardiovascular disease was treated very differently than it is today, with far less use of statins, beta blockers, blood thinners and other intensive therapies. So the effect of fish oil, even if it were minor, he said, would have been more noticeable.

斯坦博士說，有關魚油的早期研究出現在心血管疾病的治療還十分困難的時代，那時，他汀類藥物、β受體阻滯劑、血液稀釋劑和其他強化治療的使用都比現在少得多。因此，魚油的作用——哪怕十分輕微——也會較爲顯而易見。

“The standard of care is so good today that adding something as small as a fish oil capsule doesn’t move the needle of difference,” he said. “It’s hard to improve it with an intervention that’s not very strong.”

“如今的醫護水平已經非常高，多吃一顆小小的魚油膠囊不會帶來多大改觀，”他說。“要改善本來就已經十分強效的干預措施是非常困難的。”

Dr. Stein also cautions that fish oil can be hazardous when combined with aspirin or other blood thinners. “Very frequently we find people taking aspirin or a ‘super aspirin’ and they’re taking fish oil, too, and they’re bruising very easily and having nosebleeds,” he said. “And then when we stop the fish oil, it gets better.”

斯坦博士還提醒說，當與阿司匹林或其他血液稀釋劑合起用時，魚油可能會帶來危險。“我們經常發現人們在服用阿司匹林或‘超級阿司匹林’的同時服用魚油，這些人身上很容易出現青紫的瘀傷，也容易流鼻血，”他說。“當他們停止服用魚油後，情況就好轉了。”

Like many cardiologists, Dr. Stein encourages his patients to avoid fish oil supplements and focus instead on eating fatty fish at least twice a week, in line with federal guidelines on safe fish intake, because fish contains a variety of healthful nutrients other than just EPA and DHA. “We don’t recommend fish oil unless someone gets absolutely no fish in their diets,” Dr. Stein said.

像許多心臟病專家一樣，斯坦博士也鼓勵他的患者儘量不要服用魚油補充劑，而是注意每週至少食用兩次富含脂肪的魚類（遵循聯邦指南中魚肉的安全攝入量），因爲除了EPA和DHA，魚肉中還含有多種其他有益健康的營養成分。斯坦博士說：“除非飲食中完全沒有魚類，否則我們不建議服用魚油。”

But some experts say the case for fish oil remains open. Dr. JoAnn Manson, the chief of preventive medicine at Brigham and Women’s Hospital in Boston, said the large clinical trials of fish oil focused only on people who already had heart disease or were at very high risk. Fish oil has also been promoted for the prevention of a variety of other conditions, including cancer, Alzheimer’s and depression.

但一些專家稱，有關魚油的這段公案仍未了結。位於波士頓的布萊根婦女醫院(Brigham and Women’s Hospital)的預防醫學主任喬安·曼森(JoAnn Manson)博士表示，針對魚油的大型臨牀試驗只側重於那些已患有心臟病或風險非常高的人。魚油還被一些人稱作可預防多種其他疾病，如癌症、阿爾茨海默氏症和抑鬱症。

Dr. Manson is leading a five-year clinical trial, called the Vital study, of 26,000 people who are more representative of the general population. Set to be completed next year, it will determine whether fish oil and vitamin D, separately or combined, have any effect on the long-term prevention of heart disease, Type 2 diabetes, and other diseases in people who do not have many strong risk factors.

目前，曼森博士正領導開展着一項名爲“Vital”的臨牀試驗，該實驗選取2.6萬個更能代表普通人情況的人作爲研究對象，爲期五年，計劃明年完成。它將確定在無強風險因素的人羣中，魚油和維生素D（無論是單獨使用還是聯用）對於心臟病、2型糖尿病和其他疾病是否具有長期效果。

Dr. Manson says that although she recommends eating fatty fish first, she usually does not stop people from taking fish oil, in part because it does not seem to have major side effects in generally healthy people.

曼森博士說，她雖然建議優先食用富含脂肪的魚類，但一般不會阻止人們服用魚油，一部分原因是魚油對於健康的普通人似乎沒有什麼嚴重的副作用。

“But I do think people should realize that the jury is still out,” she said, “and that they may be spending a lot of money on these supplements without getting any benefit.”

“不過我認爲人們應該意識到事情沒有最後定論，”她說，“他們很可能花了很多冤枉錢買這些補充劑，卻沒能獲得任何幫助。”