Original Oily Fish Study Flawed
You’ve heard it here on ThirdAge and probably elsewhere as well: Oily fish such as salmon, fresh tuna, and swordfish are currently recommended as part of a heart healthy diet. Oops! An international team of researchers have called into question the validity of a now-classic study from the 1970s that claimed that because the diet of Eskimos in Greenland is rich in whale and seal blubber, these peopledon’t have coronary artery disease at the same rate as other populations.On the contrary, the Eskimos turn out to have alarmingly high rates of lethal CAD and stokes. The new study was done by investigators at the University of Ottawa Heart Institute in Canada, Martin Luther University in Germany, and Slovak Medical University in Slovakia andpublished online in April 2014 inthe Canadian Journal of Cardiology.
A release from the publishers quotes lead investigator George Fodor, MD, PhD, FRCPC, FAHA as saying"Considering the dismal health status of Eskimos, it is remarkable that instead of labeling their diet as dangerous to health, a hypothesis has been construed that dietary intake of marine fats prevents CAD and reduces atherosclerotic burden."
The original study, done by the Danish researchers Bang and Dyerberg, connected the low incidence of coronary artery disease (CAD) among the Eskimos to what they typically ate but the current study reports that the authors found that the Eskimos actually suffered from CAD at the same rate as their Caucasian counterparts, meaning there is insufficient evidence to back Bang and Dyerberg's assertions.
Using 40 years of new information and research, the team set out to reexamine Bang and Dyerberg's study, which is still widely cited today and is the origin of the practice of recommending the dietary addition of fish oil supplements with omega-3 fatty acids or oily fish to help avoid cardiovascular problems. However, the new review of information has determined that Bang and Dyerberg actually failed to investigate the cardiovascular health of the Eskimo population, meaning that the cardioprotective effects of their diet are unsubstantiated.
"Bang and Dyerberg's seminal studies from the 1970s are routinely invoked as 'proof' of low prevalence of CAD in Greenland Eskimos ignoring the fact that these two Danish investigators did not study the prevalence of CAD. 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," Dr. Fodor said.
Bang and Dyerberg relied mainly on annual reports produced by the Chief Medical Officer of Greenland to ascertain CAD deaths in the region. The 2014 study has identified a number of reasons that those records were likely insufficient, mainly that the rural and inaccessible nature of Greenland made it difficult for accurate records to be kept and that many people had inadequate access to medical personnel to report cardiovascular problems or heart attacks. In fact, researchers have now found that concerns about the validity of Greenland's death certificates have been raised by a number of different reports and that at the time, more than 30% of the population lived in remote outposts where no medical officer was stationed. This meant that 20% of the death certificates were completed without a doctor having examined the body.
The data collected through this new investigation shows that Eskimos do have a similar prevalence of CAD to non-Eskimo populations, and in fact, they have very high rates of mortality due to cerebrovascular events (strokes). Overall, their life expectancy is approximately 10 years less than the typical Danish population and their overall mortality is twice as high as that of non-Eskimo populations.
Many recent large and well-designed studies have shown ambiguous or negative results regarding the cardioprotective properties of omega-3 fatty acids and fish oil supplements, and yet partly based on the work of Bang and Dyerberg, they are still widely recommended as part of a heart healthy diet plan.
"Publications still referring to Bang and Dyerberg's nutritional studies as proof that Eskimos have low prevalence of CAD represent either misinterpretation of the original findings or an example of confirmation bias," concludes Dr. Fodor. "To date, more than 5000 papers have been published studying the alleged beneficial properties of omega-3 fatty acids, not to mention the billion dollar industry producing and selling fish oil capsules based on a hypothesis that was questionable from the beginning."