The importance of taking omega 6 into consideration when assessing the effects of omega 3 on myocardial infarction
Experimentally, omega-3 polyunsaturated fatty acids (PUFAs) have been shown to have beneficial cardiovascular effects, including reducing the myocardial infarct size. However, results from recent clinical trials suggest a lesser role for omega-3 PUFAs in cardiovascular health. The dichotomy between experimental studies and clinical investigation with regard to the beneficial effects of omega-3 PUFA in myocardial infarction led a team of Canadian researchers to try and identify different parameters that might be the cause. From observations in their laboratory, the authors formulated the hypothesis that the presence of omega-6 PUFA could partly explain the differences in the studies.
In a number of animal studies, supplementation with fish oil (EPA and DHA), EPA or DHA significantly reduced the infarct size in mice, rabbits and pigs (in this case, infusion in the pericardium) compared to controls and protected against ischaemia and reperfusion in isolated mouse hearts. Other studies highlight that the ratio omega-3:omega-6 must be over 1:5 for these effects to occur. Injections of resolvin E1 or D1 have also been observed to significantly reduce the infarct size in mouse and pig models of myocardial ischaemia. All the data indicate that omega-3 PUFAs and their metabolites can protect the myocardium from ischaemic injury.
With regard to clinical studies, the authors state that on the basis of such trials it is difficult to determine whether omega-3 PUFAs have positive effects on cardiovascular health (increased fish consumption probably reduces that of meat; many of the individuals studied take statins, there are microconstituents of fish and fish oil that could be beneficial to cardiovascular health, etc.). Overall, the positive effects of omega-3 PUFA are debatable.
The role of omega-6 PUFAs in cardiovascular health is controversial. Some studies link linoleic acid to lower cardiovascular risk, others conclude that arachidonic acid (AA) and some of its metabolites have proinflammatory and aggregant properties, while others argue that competition between omega-6 and omega-3 for the same metabolic pathway could reduce the beneficial effects of omega-3. Some of the metabolites of AA (such as prostacyclin and lipoxin A) have anti-inflammatory and antithrombotic properties, but it is not known whether these effects have a greater weight than those of other AA metabolites in the context of myocardial infarction.
In short, assessments of the effects of omega-3 PUFAs in myocardial infarction should bear in mind the consumption/concentration of omega-6 PUFA.