Study Suggests More Omega-3s Do Not Reduce CVD

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Back in the 1970s, population studies comparing the risk the death from coronary artery disease (CAD) between Greenland Eskimos (a.k.a. Inuit) and aged-matched Danes found the Europeans were 3 to 5 times more likely to die from heart disease [Bang HO, et al. Am J Clin Nutr 1980;33:2657-61]. The Inuit also had blood lipids and other CAD risk factors that put them at lower risk of dying from heart attacks. They had total cholesterol levels 21% lower with LDL-C that were 12% lower and serum triglyceride levels 63% lower than that of the Northern Europeans. The Inuit also had HDL-C levels about 50% higher than their European counterparts. [Bang HO, Dyerberg J. Acta Med Scand. 1972;192:85-94]. These presumably favorable changes in blood lipids were suspected to be the primary reason the Eskimo diet was far heart healthier than a typical Western diet despite the fact that the traditional Eskimo diet was high in both total fat and cholesterol. Of course, it should be pointed out that the fat content of seafood (fish and sea mammals) is much lower in saturated fatty acids (SFA) than the fat derived from land animals (cattle, pigs, and poultry) and particularly fat found in dairy products. The average Inuit diet had only 9% SFA calories compared to nearly double that amount for the average Northern European diet back in the 1970s. [Dyerberg J. Nutr Rev 1986;44:125-33]. In addition to the much lower SFA content of the Inuit diet, there were other differences in lifestyle that likely contributed to their lower risk of CAD. Eskimos were thinner with less diabetes, ate less salt and had much less hypertension and were more active than the European or Northern American populations they were being compared to. Smoking was also far more common among Western populations back in the 1970s than among Eskimos and there genetic differences too so these population studies cannot tell us specifically why the Eskimos had a low risk of dying from heart attacks. Nevertheless, the relatively low rate of CAD mortality triggered interest in the potential of omega-3 fatty acids to protect against heart disease. While omega-3 supplements have shown some presumably beneficial effects on CAD risk factors in the past more recent clinical trials have found little or no benefit to omega-3s supplements in terms of preventing cardiovascular events.

A new meta-analysis looking at the effects of omega-3 fatty acids in patients at high risk for cardiovascular events has shown that the supplements have no beneficial effects on hard clinical outcomes, including all-cause mortality, cardiac death, sudden death, heart attack, or stroke. The meta-analysis included 20 clinical trials of 68 680 patients. The mean omega-3 dose used in the clinical trials was 1.5 g/day, or 0.77 g/day eicosapentaenoic acid (EPA) and 0.60 g/day docosahexaenoic acid (DHA). The median treatment duration was two years, and the maximum was 6.2 years. There was a trend toward benefit in terms of sudden death, about a 13% reduction, and myocardial infarction, about a 10% reduction, but the decrease did not quite reach statistical significance. The strongest trend toward benefit was for the prevention of sudden death, but even this reduction failed to reach statistical significance, a finding that undermines the supposed antiarrhythmic-mediated effect of omega-3 fatty acids. [Rizos EC, et al. JAMA 2012;308:1024-33]. Results of Dr. Rizos's study are shown in Table 1 above:

Bottom Line: Omega-3 fatty acids are certainly essential fatty acids but most data suggests that people who consume at least 1 or 2 servings of fish a week get enough. Indeed, even modest fish eaters are less likely to have a heart attack and die than people who eat no seafood at all. [Kromout D. et al. N Engl J Med 1985;312:1205-9]. However, as with most nutrients, taking a fish oil supplement would most likely be beneficial only if the person taking it were actually deficient in omega-3s to begin with. Indeed, in many cases, taking supplements of nutrients in high doses can have pharmacological and toxic effects. So an important question about the clinical trials in the meta-analysis is: What was the initial omega-3 nutritional status of people in those trials? If the omega-3 supplements were not correcting an omega-3 deficiency because most of the subjects already were consuming at least 4-8oz/week of fish per week there would have been no omega-3 deficiency to correct so any beneficial effect would be due to a pharmaceutical effect. Currently, the US FDA has approved high-dose omega-3 fatty acids only for the treatment of high triglyceride levels in patients with overt hypertriglyceridemia and who are at risk of pancreatitis. The scientific evidence cannot support claims for consuming more than 8-10oz per week of omega-3-rich seafood or taking omega-3 supplements are heart healthy.

By James J. Kenney, PhD, FACN

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