Omega-3 Fish Oils Reduce Mortality from All Causes

Omega-3 Fatty Acids for Better Health

Omega-3 Fish Oils Reduce
Mortality from All Causes

Powerful evidence shows they strongly reduce triglyceride levels,
which is great for your heart
By Will Block

kepticism about modern medicine is nothing new. In an address before the Massachusetts Medical Society in 1860, the great physician and writer Oliver Wendell Holmes said, “I firmly believe that if the whole materia medica as now used could be sunk to the bottom of the sea, it would be all the better for mankind—and all the worse for the fishes.” Dr. Holmes, who was a professor of anatomy and physiology at Harvard, would doubtless be fascinated to know what we now know about certain fishes: hauling them up from the deep is good for mankind, not just for the food value they represent, but also for the medicinal value of their oils.

Fish oils—omega-3 fish oils, to be exact—are highly beneficial to human beings: they’re among our hearts’ best friends (see the sidebar). Ever since this was first surmised, in the 1970s, the evidence for the role of these fish oils in protecting us from cardiovascular disease—and from other diseases as well, including dementia, the metabolic syndrome, and perhaps cancer—has continued to mount. The medical literature now contains thousands of papers dealing with innumerable aspects of the effects of omega-3 fatty acids (which are components of the fish oils) on human physiology, especially as it pertains to cardiovascular disease.

Omega-3’s—Good for Heart and Brain

Omega-3 fish oils are called that because they’re composed in part of omega-3 fatty acids, organic acids that have a long hydrocarbon chain with several double bonds in it, the first one at the omega-3 position (third carbon from the end). When three fatty acid molecules (of any kind) are chemically bound to a molecule of glycerol (which is an alcohol), the result is a triglyceride, or fat molecule. Almost all fats of animal or plant origin are triglycerides; if the compound is a solid at room temperature, it’s a called a fat; if it’s a liquid at room temperature, it’s called an oil.

Although triglycerides are vital to your health, they can be highly detrimental, especially to your heart and brain, if their levels in your blood become too high (in that, they’re analogous to cholesterol, another potentially dangerous substance that’s vital to your health). For good heart health, therefore, and for good brain health as well, your triglycerides must be kept under control.

Furthermore, the molecular structure of the fatty acids contained in your triglycerides makes a big difference in how those fat molecules will affect your health. The most healthful fatty acids are unsaturated ones: monounsaturated or polyunsaturated. Among the polyunsaturated fatty acids (PUFAs), the most beneficial ones are the omega-3 fatty acids, or omega-3’s.

Government Sees the Light

Scientists affiliated with the Tufts-New England Medical Center in Boston recently undertook an exhaustive critical survey—a meta-analysis*—of this vast literature, and they published the results in two parts, each one a massively detailed report.1,2 The sponsoring organization was the Agency for Healthcare Research and Quality (U.S. Department of Health and Human Services), and both the request and the funding for these studies came from the Office of Dietary Supplements at the National Institutes of Health. That bespeaks a growing acceptance by the federal government of the value of some dietary supplements as agents with genuine medicinal value.

*The conclusions reached from a meta-analysis are generally more credible than those drawn from any individual study, because of the much greater statistical significance of the pooled data and the power of the mathematical techniques used to evaluate them. For more on this concept, see the sidebar “Lies, Damned Lies, and Meta-Analysis” (p. 26) in the article on horse chestnut extract in this issue.

Even the Food and Drug Administration has acknowledged the value of omega-3 fish oils: in November 2000, it issued a statement that said, in part, “Consumption of omega-3 fatty acids may reduce the risk of coronary heart disease.” Furthermore, it has ruled that up to 3 grams per day of DHA + EPA is safe for human consumption.1

This Sounds Fishy

The two most important omega-3 fatty acids for your cardiovascular health are DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid). In nature, DHA and EPA are found mainly as components of the oils of coldwater fish, notably shad (North American), mackerel (Atlantic or Pacific), salmon (virtually all species, but especially Chinook), herring (Atlantic or Pacific), anchovies (European), and tuna (especially fresh bluefin).

Another important omega-3 fatty acid, ALA (alpha-linolenic acid), is found only in plants—mainly in walnuts, butternuts, soybeans, and wheat germ, and in certain plant oils, especially flaxseed oil but also walnut, canola, soybean, and wheat germ oils. Our bodies can’t make ALA, which is an essential fatty acid in our diet; it’s essential in part because it’s the precursor to DHA and EPA. Unfortunately, though, the conversion of ALA to DHA or EPA is too slow and inefficient for optimal health purposes. It’s therefore important that we get these molecules from fish or, better yet, from omega-3 fish-oil supplements, a more reliable source for maintaining optimal levels on a daily basis.

Tufts Team Tackles Tough Assignment

The Tufts team began by screening about 7500 abstracts of research papers (in English only) on omega-3 fatty acids. For each of the two major meta-analyses—one on cardiovascular disease (CVD) clinical outcomes and one on CVD risk factors—they chose about 800 of the most promising papers to evaluate in full. For the final, detailed analysis, they then selected those relatively few dozens of papers representing the best combination of clinical relevance and methodological quality. The two meta-analyses were closely coordinated so as to be consistent in approach and complementary in coverage.

The fatty acids in a triglyceride (fat) molecule can be the same or different (these are not omega-3’s).

The tens of thousands of individuals (most of them outside the United States) who had been enrolled in the studies fell into three categories: (1) healthy adults with no known CVD or risk factors; (2) adults at increased risk for CVD due to diabetes, hypertension, or hyperlipidemia (high lipid levels, such as cholesterol and triglycerides); and (3) adults with known CVD. Depending on the circumstances, their primary intake of omega-3 fatty acids—DHA, EPA, or ALA (the precursor that all of us get from plants)—had been in the form of dietary fish, dietary fish oils, or fish-oil supplements—or, in a small minority of the studies, in the form of dietary plants, dietary plant oils, or flaxseed supplements.

Omega-3’s Improve CVD Outcomes

In the first meta-analysis (for which 39 studies passed the inclusion criteria), the investigators looked at the association between omega-3 fatty acid consumption and clinical CVD outcomes, as well as potential adverse effects from consuming omega-3’s.1 Among their findings, first of all, were that: American men consume significantly less ALA (when expressed as a percentage of total daily energy intake) than women; that youths consume less ALA than adults; and, most significantly, that people with a history of CVD consume much less ALA than people without CVD.

The catch, however, is that, although everyone gets some ALA in their diet, only 25% of the U.S. population consumes any DHA or EPA at all (and very little at that) on a daily basis. As you will see, our cardiovascular health—especially that of the highly deprived 75%—would doubtless benefit from a reversal of this situation.

The investigators found that, overall, consumption of omega-3 fatty acids from fish or fish-oil supplements significantly reduced various CVD outcomes, mainly heart attack (fatal and nonfatal), cardiac arrhythmias, angina pectoris, stroke, and death. Furthermore, it reduced all-cause mortality, i.e., death from all causes. (This does not mean that omega-3 fatty acids can save you if you’re hit by a truck, only that, on a statistical basis, consuming them regularly will reduce your overall chances of dying within a given time frame, regardless of the cause.)

The dosages of DHA + EPA used in the studies ranged from 0.3 to 8 g/day. Adverse events (mostly mild gastrointestinal upset) attributed to consumption of these compounds were described as minor. By contrast with the DHA + EPA supplements, the evidence for benefits attributable to ALA supplements was “sparse and inconclusive.”

The investigators concluded,

Overall, the evidence supports the hypothesis that consumption of omega-3 fatty acids (EPA, DHA, or ALA) from fish or from supplements of fish oil reduces all-cause mortality and various CVD events, although the evidence is strongest for fish and fish-oil supplements.

Omega-3’s Improve CVD Risk Factors

In the second meta-analysis (123 studies), the investigators looked at the association between omega-3 fatty acid consumption and a number of risk factors for CVD, including: high levels of cholesterol, triglycerides, or other lipids; high blood pressure; poor measures of glucose tolerance; and high levels of C-reactive protein.2 They found a consistently large, dose-dependent reduction in triglyceride levels associated with the omega-3’s—an effect that must surely play a role in the improved cardiac outcomes found in the first meta-analysis. The reductions ranged from 10% to 33% in various studies; as a rule, they tended to be greatest in those people with the highest baseline triglyceride levels, and they were independent of age, sex, weight, diet, etc. The dosages of DHA + EPA used in these studies ranged from 0.8 to 5.9 g/day.

The omega-3’s also reduced blood pressure by a small but significant amount (about 2 mmHg) and may have had a small effect on exercise tolerance and heart-rate variability in patients with heart disease. They had no consistent beneficial effect, however, on any of the other CVD risk factors.

Omega-3’s May Counter Arrhythmias

The Tufts group also conducted a meta-analytical study on the association of omega-3 fatty acids with many factors involved in the heart’s electrical activity, including the origin of cardiac arrhythmias—disruptions of the normal heartbeat that can lead to serious illness or sudden death.3 Here the studies they evaluated (86 out of 1807 initially considered) all involved laboratory animals, isolated animal tissues, or animal cell cultures.

Based on the evidence examined, the investigators concluded that supplementation with DHA and EPA might have anti-arrhythmic benefits when compared with a variety of other fatty acids (there was no significant effect from ALA supplementation). To the extent that this is true, it would, of course, contribute to the reduction in mortality rates definitely associated with the omega-3 fatty acids.

A Gift from the Sea

With regard to the question of the health benefits of omega-3 fatty acids, the authors of the meta-analyses said it best: “General scientific agreement supports an increased consumption of omega-3 fatty acids . . . to promote good health.”1,2 Their own work has added great weight to this assertion by providing an uncommonly solid foundation for that scientific opinion. Unquestionably, omega-3 fish oils are among the most valuable nutritional supplements available to us—a precious gift from the sea.

The three AHRQ publications cited below can be downloaded from that agency’s Web site: Click on Evidence-Based Practice, then on Dietary Supplements.

  1. Wang C, Chung M, Lichtenstein A, Balk E, Kupelnick B, DeVine D, Lawrence A, Lau J. Effects of omega-3 fatty acids on cardiovascular disease. Agency for Healthcare Research and Quality Pub. No. 04-E009-2, March 2004.
  2. Balk E, Chung M, Lichtenstein A, Chew P, Kupelnick B, Lawrence A, DeVine D, Lau J. Effects of omega-3 fatty acids on cardiovascular risk factors and intermediate markers of cardiovascular disease. Agency for Healthcare Research and Quality Pub. No. 04-E010-2, March 2004.
  3. Jordan H, Matthan N, Chung M, Balk E, Chew P, Kupelnick B, DeVine D, Lawrence A, Lichtenstein A, Lau J. Effects of omega-3 fatty acids on arrhythmogenic mechanisms in animal and isolated organ/cell culture studies. Agency for Healthcare Research and Quality Pub. No. 04-E011-2, March 2004.

Will Block is the publisher and editorial director of Life Enhancement magazine.

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