The Latest View on Omega-3 Fatty Acids

Summarized by Robert W. Griffith, MD
August 28, 2006

Summary

The latest recommendation from authoritative sources is that most people should increase their intake of two omega-3 fatty acids - EPA and DHA - by eating more fatty fish and/or taking appropriate supplements.

Introduction

This article is an attempt to make sense of the jumble of names involved when we speak of long-chain fatty acids, and bring you the latest view on omega-3 fatty acids in particular. It's based on a review of the available literature done by Tufts University scientists and published in the American Journal of Clinical Nutrition, along with a helpful editorial.

Information has gradually accumulated in recent years about the possible protective effect of omega-3 fatty acids found in fatty fish and fish-oil supplements on the risk of cardiovascular disease. In 2004 the FDA announced a 'qualified health claim' for these substances, which has allowed some advertising of the potential benefits to emerge.

What they are

The omega-3s are polyunsaturated fatty acids, which means that the fatty acid chain contains a number of double bonds. The actual omega-3 designation means the first double bond occurs in the third carbon-carbon link of the chain. The Important omega-3 fatty acids in human nutrition are: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and α-linolenic acid (ALA). The first two are found chiefly in fatty fish (salmon, lake trout, tuna and herring) and fish oils, while ALA is found in vegetable oils (flaxseed, canola, soybean) and walnuts. In man, less than 5% of ALA is converted to EPA or DHA.

How they may work

Omega-3 fatty acids may exert their effect on cardiovascular disease by decreasing heartbeat irregularities (arrhythmias), lowering blood triglyceride levels, lowering blood pressure, and decreasing blood platelet aggregation (a clotting mechanism). Unfortunately, most of the evidence for these effects comes from laboratory studies rather than clinical trials, so that the relative importance of each is uncertain. Definitive clinical work is required.

The review of clinical data

Of the 842 articles reviewed, only 46 met the strict quality criteria that were established. Even then, the study designs, background diets, baseline fish or omega-3 intake, and endpoint definitions in the available studies were so variable that a combined analysis (a meta-analysis) was not possible. There were few studies that include evaluation of the dietary omega-6 fatty acid; the omega-6s (arachidonic acid and linoleic acid, for example, found in cereals, whole grains, and most vegetable oils) are involved in prostaglandin synthesis and inflammatory responses. (A lower ratio of dietary omega-6 to omega-3 fatty acids is desirable in lowering the risk of many of the chronic diseases in Western societies.)

Overall, the evidence from the analysis of these 46 studies indicated that increased consumption of EPA and DHA, either through fish or supplements (or both), reduced the rates of death from any cause, heart attack, sudden heart death, and stroke. The protective effect of these omega-3 fatty acids was more readily established in so-called secondary prevention studies, rather than in primary prevention¹. ALA was without much effect in reducing cardiovascular disease.

What we still don't know

This latest review of omega-3 fatty acid effects reveals several areas where our knowledge is seriously lacking:

• Would reducing omega-6 fatty acid intake enhance the benefits of increased omega-3 intake?
• Would measuring blood or tissue levels of EPA and DHA make it easier to see if supplements are necessary?
• How exactly do the omega-3s work? (see second paragraph above.)
• Which is most effective in lowering cardiovascular disease - EPA or DHA - or are they both needed?

In the meantime...

Based on results from all the studies examined, adverse effects of taking supplements were mild - slight nausea and vomiting, for example. One report linked high ALA blood levels to an increased risk of prostate cancer. It seems, therefore, that it's safe to support the recommendation of the editorialists: "In the United States, certainly, and in other countries where omega-3 fatty acid consumption is low, public health initiatives are needed to increase intakes of EPA and DHA." This means eat more fatty fish; the potential risk of fish toxins is smaller than the risk of too low EPA and DHA levels. Alternatively, one can take an appropriate supplement.

Sources

• N-3 fatty acids from fish or fish-oil supplements, but not α-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: a systematic review. C. Wang, WS. Harris , M. Chung,  et al., Am J Clin Nutr, 2006, vol. 84, pp. 5--17



• N-3 fatty acids and cardiovascular disease: navigating toward recommendations. Editorial. RJ. Deckelbaum, SR. Akabas, Am J Clin Nutr, 2006, vol. 84, pp. 1--2

Footnotes
1. Secondary prevention is lowering the risk of an event (e.g. sudden cardiac death) following survival of an initial event (e.g. a heart attack). Primary prevention is lowering the risk of the initial event (the heart attack).

Related Links
FDA News (2004)
High Blood Levels of Omega-3s May Lower Your Risk of Death
Omega 3 for Neck or Back Pain

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