Omega-3 index could be goalposts for max heart health
are beneficial to heart health, and proposes a new measure of
cardiovascular risk called the "omega-3 index".
The measure, merely a quantification of the fatty acid status of a person, could help physicians and heart patients achieve levels of omega-3 that are reported scientifically to provide cardiovascular benefits.
"As is the case now for LDL [so-called 'bad' cholesterol], in the future cardiac societies might very well recommend [intake of] EPA and DHA to become goal orientated," wrote Clemens von Schacky from Ludwig-Maximilians-Universitat in Munich, and William Harris from the University of South Dakota.
Omega-3 fatty acids have been linked to a wide-range of health benefits, including cardiovascular disease (CVD), good development of a baby during pregnancy, joint health, behaviour and mood, and certain cancers.
But some much publicised studies, and in particular a recent meta-analysis (British Medical Journal, doi: bmj.38755.366331.2F), have claimed that there was no evidence linking omega-3 intake and improvements in heart health.
However, the BMJ review contained several flaws, said von Schacky and Harris, including the exclusion of biomarker studies and relevant cohort studies, inclusion of a study with "questionable scientific integrity", and combining studies from vastly different population groups.
Their new review, published on-line ahead of print in the Elsevier journal Cardiovascular Research (doi: 10.1016/j.cardiores.2006.08.019), reviewed epidemiological and four large scale intervention studies, and concluded that the majority of the evidence supports the benefits of omega-3 intake for heart health.
The mechanism behind such benefits, said von Schacky and Harris, is proposed to be the incorporation of EPA and DHA into cell membranes, which replaces other fatty acids and changes the properties of the cell.
Such changes include expanding blood vessels to improve blood flow, reducing inflammation, and lowering blood triglyceride levels.
And since the omega-3 are incorporated into the cell it would be worthwhile measuring the omega-3 cellular content as a marker of cardiovascular risk, said von Schacky and Harris.
"The possibility that an omega-3 biomarker might have clinical prognostic utility, must be considered," they said.
Von Schacky and Harris proposed, therefore, the "omega-3 index", defined as the percentage of EPA plus DHA in red blood cell membranes, relative to all other fatty acids.
Using data from the scientific literature, the reviewers calculated that an omega-3 index value of eight per cent or above is associated with a 90 per cent reduction in the risk of sudden cardiac death, compared to a value of four per cent or less.
"The standard dose of one gram per day of the omega-3 fatty acids, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), recommended by the cardiac societies is probably far from ideal for everybody, since not only this standard dose, but also diet, individual genetic background, BMI… and other factors all taken together probably determine the omega-3 fatty acid status of a given person," wrote the reviewers.
The risk of pollutants from oily fish, such a methyl mercury, dioxins, and polychlorinated biphenols (PCBs) have led to some to advocate a reduction in fresh fish intake, despite others advising that the benefits of fish consumption outweigh the risks.
Such conflicting views on fish intake have seen the number of omega-3 enriched or fortified products on the market increase as consumers seek omega-3s from 'safer' sources. Most extracted fish oil are molecularly distilled and steam deodorised to remove contaminants.
Indeed, von Schacky and Harris recommend that such contaminants be avoided.
Fears about dwindling fish stocks have pushed some academia and industry to start producing omega-3s from alternative sources, such as algae extraction. Indeed, companies such as Martek Biosciences and Lonza are already offering algae-derived omega-3 DHA as a dietary supplement.
