1970s fish oil study criticized

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January 2015

The 1970s studies that set the stage for decades of ongoing research on the heart benefits of omega-3 fatty acids have recently come under attack. A 2014 review article highlights the alleged flaws of the studies that revealed a correlation between a high-marine-fat diet, low serum lipid levels, and low incidence of heart disease among Greenland Inuits. But are the allegations true? One of the studies’ original authors, Jørn Dyerberg, now an emeritus professor at the University of Copenhagen, says no.

A Surprising Finding About Fish

Nearly five decades ago, a team of Danish researchers set out to understand how the Inuit population in Greenland could have such a low incidence of heart disease and diabetes despite a diet with high levels of marine fat. Their initial findings, published in The Lancet in June 1971, surprised them: The average Greenland Inuit had lower serum cholesterol and lipid levels than the average Dane. Their levels were also lower than Inuits who lived in Denmark, suggesting an environmental, and not genetic, explanation. The findings begged the question: Could a diet high in oily coldwater fish actually be the secret to good heart health? The study did not claim to answer this question but rather proposed it as an area of future investigation.

To this day, that 1971 study continues to be cited as the first to show a possible connection between fish oil and heart health. Denmark’s Aalborg Hospital North researchers Hans Olaf Bang, Jørn Dyerberg, and Aase Brøndum Nielsen analyzed the plasma-lipid pattern of 130 Greenland Inuits in the northern part of Greenland’s west coast. The team determined the concentrations of plasma lipids, cholesterol, and triglycerides in both men and women age 30 and above, and compared them to the levels in a Danish control group. In nearly all categories, lipid concentrations were significantly lower among Inuits than Danes, and the net difference increased with age. This was the first study to thoroughly examine the serum-lipid pattern of both of these populations.

“In the [Inuits] the association of low level of most types of lipid (except α-lipoproteins) with very low incidence of ischaemic heart-disease is striking,” the authors wrote, “but not necessarily causal . . . The food of the [Inuits] still living as hunters and/or fishermen consists mostly of meat of whales, seals, sea birds and fish . . . [which] is extremely rich in protein and fat.” To explain how a diet so high in animal fat could coincide with low plasma cholesterol levels, the authors speculated that the large amount of polyunsaturated fatty acids in marine food could be protective against increasing plasma-cholesterol levels, and thus protective against heart disease—a view that followed the thinking of that time.

A series of follow-up studies published over the next decade revealed more detailed information about the Inuit diet and other health factors. The researchers did not collect their own data on the incidence of heart disease among the Inuits but rather received this information from reports compiled by the chief medical officer in Greenland.

A Harsh Critique Attracts Media Attention

In April 2014, George J. Fodor, University of Ottawa Heart Institute professor, and coworkers, published a paper in the Canadian Journal of Cardiology titled “‘Fishing’ for the origins of the ‘Eskimos and heart disease’ story. Facts or wishful thinking? A review” The critical review caught the attention of several mainstream media outlets, which ran stories with headlines such as, “The Fishy Origins of the Fish Oil Craze” and “Fish Oil May Not Prevent Heart Disease After All”.

In the article, the authors state their biggest issue with Bang and Dyerberg’s studies is that they did not directly examine the cardiovascular status of Greenland Inuits, relying instead on data from the annual reports from the chief medical officer in Greenland. These reports, which show deaths due to coronary artery disease in the 1960s ranging from 8.5% to 11.8% of total deaths, “have limited validity,” the authors claim. “These reports are based on death certificates and hospital admissions.” However, about a third of the population lived in small settlements, far from hospitals and medical officers, both of which had “limited diagnostic facilities,” leading the authors to conclude “the reported data are likely an underestimation of the true magnitude of the disease in this area.

“Bang and Dyerberg’s seminal studies from the 1970s are routinely invoked as ‘proof’ of low prevalence of [coronary artery disease, or CAD] in Greenland Eskimos ignoring the fact that these two Danish investigators did not study the prevalence of CAD,” Fodor et al. wrote. “Instead, their research focused on the dietary habits of Eskimos and offered only speculation that the high intake of marine fats exerted a protective effect on coronary arteries.”

A Response From One of The Original Authors

It seems one of the things that bothers Fodor and his colleagues about the 1970s study is that, to this day, many researchers credit Bang and Dyerberg for finding out Inuits had low rates of heart disease. “Nobody even, obviously, read this paper!” Fodor told Slate. (Inform contacted Fodor, but he was not available for comment).

But it’s not their fault that people misquote the decades-old papers as proof that fish promote heart health, Dyerberg told Inform. That was not their intention and they never made that claim. The studies were meant to generate hypotheses that could be further investigated with interventional studies, he said.

“We based our statement of the rare occurrence of acute myocardial infarction in Greenland on a meticulous review [of the data that were] available at that time,” Dyerberg said. The data from the chief medical officer of Greenland were consistent with slightly older epidemiological data on medial deaths in northern Greenland.

“They’re trying to disprove the story by saying that the epidemiological data from Greenland way back in the ‘70s and earlier were not correct, so the story is not correct, which is, of course, bogus,” he said. “The only [way to] prove or disprove whether there’s a connection between diet and disease pattern is by doing an intervention study. I’ve been a professor of human nutrition for many years and I know it’s difficult, but that’s the only way you can do it. And there have been several studies, some finding a positive and others finding not a positive association between fish intake and cardiovascular heart disease. But most of them are positive.

“The cardiovascular story is rather solid but has some weak points,” Dyerberg added. “But then it has opened up for a lot of other interesting aspects of the story,” such as the lack of long-chain omega-3 fatty acids in the Western diet and the medical consequences that have resulted.

Dyerberg pointed out several times in the 2014 review article where Fodor et al. twisted the facts and misquoted basic papers in an effort to make the data fit into their fish-oil-debunking narrative. For example, they cite another one of Dyerberg’s papers, published in 1988 in the International Journal of Epidemiology, which found that Greenland Inuits have a similar prevalence of cardiovascular heart disease and a mortality rate twice as high as non-Inuit population, which is correct. But the authors failed to mention another significant finding from that report, which is that people living in Greenland settlements have lower incidence of ischemic heart disease. It wouldn’t have fit into their narrative—that there is no evidence that fish have heart health benefits—so they left it out, Dyerberg said, which is a deliberate twisting of the facts in an attempt to gain attention. “It’s nice to have attention, but you shouldn’t use science for that.”

Fodor et al. also cite data that shows Greenland Inuits do not have lower rates of cardiovascular heart disease and acute myocardial infarction today as evidence that the data from half a century ago is flawed.

This is a weak argument, Dyerberg said. That does not disprove that it was that way back then, “and we only had the data that we had. Of course, you can put a question mark on anything, but this doesn’t disprove anything.”

Dyerberg said his response to the review article by Fodor et al., in a nutshell, is: “And so what?

“The only one[s] who didn’t do any studies are Fodor and his companions,” he said. “They just quoted the literature; they misquoted a lot of it . . . I’m not annoyed, I’m just bewildered why they do it.”

But negative stories are always interesting, he said, which may explain why the article caught the attention of mainstream media, despite its flaws. Dyerberg said he was not contacted by any media outlet, other than Inform, for comment on this 2014 critique of his decades-old studies. He continues to stand by the recommendations of the American Heart Association and other international organizations that recommend two or three servings of coldwater, fatty fish a week because, he said, the evidence is sufficient that the long-chain omega-3 fatty acids found in fish are beneficial for health.