Recent results add to the evidence that marine omega-3s bring consumers’ triglyceride-lowering, anti-clotting benefits
by Craig Weatherby
While the claim that high blood cholesterol levels cause cardiovascular disease is increasingly discredited—they're more likely a marker for other problems—the risks of high blood levels of triglycerides and pro-clotting factors are very clear.
In fact, the American Heart Association’s advice to take 1,000 mg of fish oil daily has nothing to do with people’s cholesterol profiles. Omega-3s raise blood levels of both “good” (HDL) and “bad” (LDL) cholesterol: effects that cancel each other out.
Instead, their recommendation to take fish oil stems from the ability of the long-chain omega-3 fatty acids (DHA and EPA) in fish to drop triglyceride levels dramatically. (They also reduce inflammation and enhance blood flow while regularizing heart rhythms, but that's another story.)
The AHA recommends even higher doses for heart patients whose triglyceride levels are higher than 200 mg per deciliter.
The positive findings from three recent publications—a medical trifecta, if you will —confirm and clarify key cardiac benefits often attributed to the omega-3s in fish oil:
- They lower unhealthily high triglyceride levels.
- They possess powerful anti-clotting properties.
One of the new studies confirms that oily fish are the best bets for cardiovascular health, while another gives omega-3 DHA its due as a cardiovascular-health companion to omega-3 EPA.
Perhaps just as importantly, some of these recent results confirm the dangers of diets high in omega-6 fatty acids.
Perhaps just as importantly, some of these recent results confirm the dangers of diets high in omega-6 fatty acids: metabolic competitors with omega-3s that predominate in most vegetable oils—especially corn, soy, cottonseed, canola, safflower and sunflower—and therefore dominate American diets (The only exceptions are olive, macadamia nut, and hi-oleic sunflower oils).
Oily fish beat lean at lowering triglycerides; lower-omega-6 cooking oil helps
British researchers recruited 142 people for a six-month-long randomized, controlled clinical trial study whose findings were published last fall (Moore CS et al 2006).
They divided the participants into a control group (no changes to regular diet) and one of four experimental-diet groups.
During the trial, the four experimental groups used one of two vegetable oils—sunflower or canola—exclusively, to test the effects of oils with different levels of omega-3 (anti-inflammatory, anti-coagulant) fatty acids and omega-6 (pro-inflammatory, pro-coagulant) fatty acids:
- Sunflower oil is very high in pro-inflammatory, pro-coagulant omega-6 fatty acids and very low in anti-inflammatory, anti-coagulant omega-3 fats.
- Canola oil is considerably higher in omega-3 fats and lower in omega-6 fats.
These were the four experimental regimens, in descending order of their omega-3 content. That is, group one’s dietary additions provided the highest omega-3 content while group four’s additions provided the least amount:
- Two portions of oily fish (4.5 grams EPA + DHA) per week, plus canola oil
- Two portions of oily fish (4.5 grams EPA + DHA) per week, plus sunflower oil
- Two portions of lean fish (0.7 grams EPA + DHA) per week, plus canola oil
- Two portions of lean fish (0.7 grams EPA + DHA) per week, plus sunflower oil
After six months, the two oily fish groups (one and two) showed substantially lower blood triglyceride levels compared with the “lean fish + sunflower oil” group (four).
As expected, the reductions in blood triglyceride levels were greatest in the “oily fish + canola oil” group, who had the highest omega-3 intake and lowest omega-6 intake.
Surprisingly, even the control group, who were not asked to make any dietary changes, showed lower blood triglyceride levels compared with the “lean fish + sunflower oil” group: an outcome that suggests that high intake of omega-6 fatty acids is bad for blood chemistry.
Note: An earlier trial showed that fish oil lowered triglycerides equally effectively in the context of diets containing either moderate or high levels of omega-6 fats. However, the authors did not examine levels of pro-clotting factors (Brady LM et al 2004).
While the interactions of omega-6 and omega-3 fats need more study, the superiority of omega-3s for cardiovascular health is by now clear and unquestioned.
Modest omega-3 intake lowers triglycerides: DHA works well alone
Of the two omega-3 fatty acids in fish oil—EPA and DHA—it’s been thought that EPA is the more powerful aid to heart health. But this presumption has been challenged in recent years, and a trial from Colorado published last month further undermines this belief (Schwellenbach LJ et al 2006).
Researchers at Kaiser Permanente in Aurora, Colorado conducted a randomized, double-blind trial in 116 heart patients (average age 69.4 years, 70 percent men) whose triglyceride levels were higher than 200 mg per deciliter.
The coronary heart disease patients were divided them into two groups:
- Group 1 took 1000 mg of DHA for eight weeks
- Group 2 took 1,252 mg of DHA + EPA for eight weeks.
After two months, blood triglyceride levels in the DHA-only group fell by an average of 21.8 percent, versus an 18.3 percent drop in the DHA + EPA group, with the difference deemed statistically insignificant.
In addition, a higher proportion of the people in the DHA group (24.6 percent) achieved the goal of lowering triglyceride levels to less than 150 mg/dL, compared to the DHA + EPA group (10.2 percent).
The Colorado team came to an obvious conclusion (our clarifications in brackets ): “Our results indicate that the American Heart Association recommended cardio-protective dose of omega-3 fatty acids can also significantly lower triglycerides in patients with CAD. There do not appear to be significant differences in triglyceride-lowering between DHA only and DHA + EPA combination products when dosing is based on [the same amount of] DHA.” (Schwellenbach LJ et al 2006)
Note: Since we know that EPA and DHA have different bodily functions and benefits, it makes good sense to take both: the point of this study is simply that DHA deserves more credit for fish oil's cardiac benefits than it usually receives.
Dutch clinical trials confirm blood fat and clotting benefits
Earlier this month, researchers at Holland’s Maastricht University published the results of two clinical trials.
These trials were designed to gauge the ability of fish oil to reduce undesirably high blood levels of triglycerides and clot-promoting chemicals: cardiovascular risk factors considered equally or more important than people’s cholesterol profiles (Vanschoonbeek K et al 2007).
Study #1: Uncontrolled trial in overweight men
This trial involved 54 overweight men without cardiovascular disease, hypertension, or diabetes, none of whom were taking cardiac medications.
Blood samples were collected at the beginning of the trial and after four weeks of fish oil intake. All the men took fish oil capsules containing 3.1 grams of omega-3s per day (2,025 mg EPA and 1,125 mg DHA).
Study #2: Controlled trial in overweight diabetics
The second study involved 42 overweight patients with type 2 diabetes (26 men and 16 women), who were divided into two groups:
- 20 participants took the same fish oil regimen as the men in Study #1.
- 22 participants took corn oil capsules high in omega-6 fatty acids (linoleic acid).
Blood samples were collected at the beginning of the trial and after eight weeks of taking either fish oil or corn oil capsules.
Results: Fish oil improve unhealthy blood profiles; Diabetics get biggest benefits
The Dutch researches found that the participants with the highest blood triglyceride and cholesterol levels also had the highest levels of various factors that promote the unhealthful blood clotting tendencies associated with risk of clogged arteries and cardiac death (i.e., prothrombin, fibrinogen, factor V, factor VII and factor X).
Among the study #1 participants taking fish oil, those with the highest blood levels of triglycerides and pro-clotting agents also enjoyed the greatest reductions in these risk factors, but the effect was small, and weaker than seen in a previous trial conducted by the same Dutch team (Vanschoonbeek K et al 2004).
In study #2, the diabetics in the fish oil group who had the unhealthiest blood profiles enjoyed the biggest drop in blood levels of triglycerides and pro-clotting agents: reductions greater than those seen in the healthy overweight men in Study #1.
In contrast, the study #2 participants who took corn oil saw no improvements.
Overall, the people in the fish oil groups of studies # 1 and 2 enjoyed decreases in three-quarters of the blood-clotting factors measured—with the diabetics seeing the biggest drops by far.
In contrast, the corn oil groups in studies # 1 and 2 suffered increases in two-thirds of these pro-clotting factors.
Overall, the fish oil groups showed increases in levels of HDL (“good”) cholesterol and LDL (“bad”) cholesterol alike, while the corn oil (omega-6 fatty acid) group showed only reductions in HDL cholesterol and rises in LDL cholesterol.
In other words, omega-3-rich fish oil produced changes in blood fats and pro-clotting factors far preferable to those produced by omega-6 fatty acids.
- Moore CS, Bryant SP, Mishra GD, Krebs JD, Browning LM, Miller GJ, Jebb SA. Oily fish reduces plasma triacylglycerols: a primary prevention study in overweight men and women. Nutrition. 2006 Oct;22(10):1012-1024.
- Vanschoonbeek K, Feijge MA, Saris WH, de Maat MP, Heemskerk JW. Plasma triacylglycerol and coagulation factor concentrations predict the anticoagulant effect of dietary fish oil in overweight subjects. J Nutr. 2007 Jan;137(1):7-13.
- Vanschoonbeek K, Feijge MAH, Paquay M, Rosing J, Saris W, Kluft C, Giesen PL, de Maat MP, Heemskerk JWM. Variable hypocoagulant effect of fish oil intake in humans: modulation of fibrinogen level and thrombin generation. Arterioscler Thromb Vasc Biol. 2004;24:1734–40.
- Schwellenbach LJ, Olson KL, McConnell KJ, Stolcpart RS, Nash JD, Merenich JA. The triglyceride-lowering effects of a modest dose of docosahexaenoic acid alone versus in combination with low dose eicosapentaenoic acid in patients with coronary artery disease and elevated triglycerides. J Am Coll Nutr. 2006 Dec;25(6):480-5.
- Brady LM, Lovegrove SS, Lesauvage SV, Gower BA, Minihane AM, Williams CM, Lovegrove JA. Increased n-6 polyunsaturated fatty acids do not attenuate the effects of long-chain n-3 polyunsaturated fatty acids on insulin sensitivity or triacylglycerol reduction in Indian Asians. Am J Clin Nutr. 2004 Jun;79(6):983-91.