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Fish oil: a cautionary tale of how diet ideas persist despite contradictory evidence

Fish oil supplements
A 2014 paper that reviewed 24 previously published studies reported that 22 of those studies showed no benefit for fish oil.

In a terrific article published last week in the Washington Post, reporter Peter Whoriskey explains how fish oil supplements may exemplify “the human weakness for anything touted as a life-extending elixir.”

The supplements also offer a cautionary tale, he says, of how “diet notions can persist even when stronger evidence emerges contradicting them.” 

“People in the United States spend about $1.2 billion annually for fish oil pills and related supplements even though the vast majority of research published recently in major journals provides no evidence of a health benefit,” Whoriskey writes. “The ‘accrual of high-level evidence,’ according to a review of studies published last year in an American Medical Association journal, shows ‘that the supplements lack efficacy across a range of health outcomes.”

Yet health claims for fish oil supplements continue to be made — even on the website for the American Heart Association and, until recently, it seems, on some (but not all) of the websites for the National Institutes of Health.* 

Scientists and health officials are often just as reluctant as the general public to let go of disproven ideas. As Whoriskey also notes in his article, that’s been the case with many other pills as well, including vitamin E, beta-carotene and estrogen.

Started in Greenland

The fish oil story began, writes Whoriskey, in the 1970s, when two Danish scientists, Hans Olaf Bang and Jorn Dyerberg, observed the diets of people living in the remote Inuit villages of northwest Greenland:

The people in those villages ate mostly whale, seals and fish, according to the scientists. While orthodox thinking at the time suggested that a diet so rich in animal fat would cause heart disease, reports of heart attacks there were very few. Bang and Dyerberg were intrigued.

During their visit, they drew blood samples of 130 Inuits. The samples showed low levels of cholesterol and triglycerides, which are viewed as markers of heart disease.

Eventually, the two formally would hypothesize that the low levels of heart disease among the Inuit was caused by the omega-3s in their fishy diets.

One of the first major tests of this idea was published in the British medical journal the Lancet in 1989. The test, often referred to as the DART study, looked at more than 2,000 Welsh men who had suffered heart attack; some were told to eat more oily fish. That group, it turned out, was 29 percent less likely to die over the next two years.

No solid evidence

That finding triggered a demand for fish oil supplements, and sales climbed into the tens of millions by the mid-1990s, reports Whoriskey. Sales soared even more after the AHA issued a “scientific statement” in 2002 that concluded “omega-3 fatty acids have been shown in epidemiological and clinical trials to reduce the incidence of cardiovascular disease.”

But that statement was actually based on mixed evidence, as Whoriskey explains:

Some of the observational studies at the time showed that eating fish provided a benefit; others didn’t. Two randomized trials showed a benefit, while a third didn’t. At the same time, consuming fish and fish oil didn’t show harmful effects, either.

Bill Harris, one of the three authors of the AHA statement, said that currently the “evidence is unclear” on the benefits of fish oils.

But “it all made a lot of sense at the time,” said Harris, now a professor at the University of South Dakota. He is also president of OmegaQuant, a company that analyzes the content of foods. “There seemed to be a benefit, and they were safe, so there was just no downside. Everything looked good, so why not do it?”

A year after the AHA released its statement about fish oil, researchers published a follow-up to the DART study. Writes Whoriskey:

Of 3,000 Welsh men with angina — a chest pain caused by coronary heart disease — some were advised to eat oily fish or take fish oil supplements. This time, the fish group patients were more likely to die, and the researchers said it was particularly worse for those taking the fish oil pills.

“The excess risk [of cardiac death] was largely located among the subgroup given fish oil capsules,” they reported.

People keep believing 

By then, though, the idea that fish oil reduced the risk of heart disease was fixed in people’s minds. Fish oil supplements kept flying off the shelves, even though, as Whoriskey notes, “the pages of the academic journals were filling with evidence that fish oil has no benefits.”

A 2014 paper that reviewed 24 previously published studies reported, for example, that 22 of those studies showed no benefit for fish oil.

Of course, it’s possible, says Whoriskey, that fish oil has some health benefits that current science is unable to detect. And a clinical trial involving 26,000 people is currently under way to try to sort that out.

Still, as JoAnn E. Manson, the principal investigator of that trial and the chief of preventive medicine at the Harvard-affiliated Brigham and Women’s Hospital in Boston, told Whoriskey, “It’s amazing how popular the fish oil supplements have become without conclusive evidence of their efficacy.”

You can read Whoriskey’s article on the Washington Post’s website.

* The NIH page with the positive statement about fish oil, which Whorisky links to in his article, appears to no longer exist.

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Comments (2)

  1. Submitted by Chris Foley on 07/14/2015 - 11:27 pm.

    Really?

    So all those placebo controlled double blind trials of the past 25 years showing significant risk reduction from EFAs (essential fatty acids/polyunsaturated fatty acids) from everything from dementia to ventricular arrhythmias were just made up? And the trial of 26,000 people is going to tell us some of the same truths that led us all to the belief that dietary cholesterol was evil and that statins for primary prevention are safe and effective? Please, ma’am, the reading public is getting smarter than that. The next thing you know we will be told that “7-10 servings of grains everyday” is a great idea. Oh wait…

    Using only significant coronary events as endpoints is fraught with hazards. Does the public know that using this kind of endpoint, ~ 50% of major coronary events occur in people with normal lipid profiles? Perhaps that might be a nice follow up story for you.

    And the obtuse comment by Whoriskey that in the Welsh study the people taking only fish oil capsules had the worst outcomes overlooks the likelihood that those “only taking fish oil capsules” very possibly had terrible diets otherwise since that was the ONLY source of EFAs.

    Again, statistically this USA Today style drive-by review of a WashPo driveby review is a tad “shallow” and leaves the undereducated reader with a terrible impression that EFAs from the seafood chain are a hoax. If you want to write about hoaxes, then let’s start with statin drugs, flu shots, and the absence of a coherent community vitamin D policy on the part of our brilliant 3rd party administrators in health care.

  2. Submitted by RB Holbrook on 07/15/2015 - 10:18 am.

    Other Damage

    Fish oil capsules are also beginning to cause environmental damage to the oceans. The fish from which the oil is extracted is bottom-feeding “trash” fish that generally is not sold for human consumption. It is, however, a prime food source for fish like sea bass or salmon, which we do eat, and which are a healthier source of protein than red meat. Continued trawling for these fish is disrupting the aquatic food chain for health benefits (if any) that cold be obtained in other, less damaging ways.

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