Cardiovascular disease, omega 3 and the study from the wrong conclusions

Heart disease: omega 3 expert clarifies all doubts about it

Prof. William S. Harris, a world authority on the role of omega-3s in cardiovascular disease, criticizes the scientific basis for invalidating the conclusions of a recent meta-analysis that cast doubt on the benefits of these fatty acids. The doubts raised recently about the usefulness of taking Omega-3s to reduce the risk of cardiovascular disease are not borne out by the facts and the study. This is said by Prof. William S. Harris, professor of medicine at the University of South Dakota (Sioux Falls, USA) and an expert on Omega-3, in response to findings published by Evangelos Rizos and colleagues in the Journal of the American Medical ^Association1 (JAMA). According to Harris, Rizos and colleagues came to too definitive conclusions based on a statistical analysis that was much more restrictive than those normally conducted and accepted by the scientific community. 

Omega-3 and cardiovascular disease, why there is doubt 

The first studies on the benefits of Omega-3s for the cardiovascular system date back to the 1970s. Since then, researchers have gathered more and more evidence in favor of the hypothesis that increasing intake of these fatty acids protects against diseases affecting the heart and blood vessels. Rizos and colleagues reviewed the results of 20 studies involving a total of about 70,000 individuals to find out whether intake of the Omega-3s in fish oil really reduces the risk of heart attacks, strokes or premature death due to cardiovascular problems. The purpose of the analysis, not the first of its kind, was to shed light on a topical issue. In fact, the authors' conclusions created more confusion on the topic. According to Harris, this confusion stems from the overly sharp and generalized claims made by Rizos and colleagues, which are based on a statistical analysis that is much more restrictive than the standards of the scientific community. 

The importance of proper statistical analysis 

The authors of the analysis published in JAMA concluded that Omega-3s exert no statistically significant benefit on cardiovascular disease risk. But what, exactly, does the phrase "statistically significant" mean in their intepretation? Statistical significance does not represent a certainty, but a probability. A statistically significant result is one that is much more likely to be true than false. When researchers perform a statistical analysis, they choose how large the probability of the result being wrong should be. Rizos and colleagues decided to set the parameters of their analysis by reducing this probability much more than scientists normally do. This arbitrary choice made the association between fish oil and reduced cardiovascular risk statistically insignificant. Harris explained that maintaining the standard statistical parameters would instead have shown thatfish oil reduces the risk of death from heart diseaseby 9 percent. Of the 16 such analyses done on different topics and published by JAMA in 2012, Rizos' was the only one that changed the statistical parameters. This entirely subjective choice turned a favorable effect of omega 3 into a non-effect. 

Too low amounts of omega 3? 

Harris also addressed another technical aspect of the studies involved in this analysis, pointing out that in 84 percent of the cases omega-3 was taken in the form of ethyl esters. According to recent research, this particular form of omega-3 is absorbed very little when taken on an empty stomach (24). This means that, in reality, most of the 70,000 individuals involved in the analysis may have been taking too low doses of Omega-3 to be beneficial. 

Is it fair to generalize the results? 

If those concerning statistics and doses taken are rather technical details, the interpretation of the results is much less so, and according to Harris, the conclusions reached by Rizos and colleagues are too stark. The expert points out that, precisely because of current knowledge about the benefits of Omega-3 intake, it would have been more correct to make distinctions based on the clinical picture of patients who took these fatty acids. Harris agrees, for example, that in patients with an average age of 63 years who have been diagnosed with cardiovascular disease and are undergoing optimal medical therapy, taking about 1 gram per day of Omega-3 for 2 years does not reduce the risks to the heart and arteries any more than the medical treatment already underway. The situation may be different for those taking larger doses of Omega-3 or taking 1 gram but for more than 2 years. Rizo's analysis also does not show that Omega-3s provide any benefit to patients at an earlier stage of the disease or who are not receiving optimal care. For these reasons, according to Harris, the results of this extensive analysis cannot be applied to reality. 

Source:

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