Fish-based EFAs increase certain risks.
Studies have found that there is a significant reduction of vitamin E in the liver and plasma when DHA is taken without vitamin E supplementation.1 Not only is there is a close relationship between peroxidation and cardiovascular diseases, but also other diseases including cancers, cataracts, immune system decline, and brain dysfunction.
Therefore, those who take fish oil supplements or whose diets are high in fish are strongly advised to take added vitamin E supplements. This is the main advantage to consuming ALA rather than DHA and EPA from fish. Even high intakes of ALA from plant-based oils do not cause a vitamin E deficiency, but fish oil and other DHA and EPA supplements can.2
The formation and progression of atherosclerosis have been directly linked to lipid peroxidation (the deterioration of the EFAs that cause trans fats). When DHA was used to decrease this risk, DHA was transformed into a promoter of the disease when there was not enough antioxidants present.3
Some researchers are expressing concern that fish oil supplements appear to depress the immune system’s response to infection. Moderate to high intakes of EPA but not of ALA can decrease natural killer (NK) cell activity in healthy subjects.4 Natural killer cells play an important role in defending the body against viral infections. Researchers at Tufts University Human Nutrition Center have determined that fish oil reduces the production of T-cells and other lymphocytes by at least 63 percent and actually use this method to create vitamin E deficiencies in their experiments: “Feeding of fish oil has been a classic method for inducing vitamin E deficiency in laboratory experiments. 5
Another risk factor is aimed at those taking anticoagulants (blood thinners), especially aspirin, warfarin, dalteparin, and enoxaparin. Fish oil tends to intensify blood-thinning effects; and these patients are at a greater risk for bleeding episodes, including internal bleeding. While blood-thinners help prevent heart attacks, they can increase the risk of hemorrhagic stroke. Therefore, those on anticoagulants and those with high blood pressure are advised not to take fish oil supplements.6
Diabetics are at greater risk for heart disease and are now being advised not to use fish oil supplements. Although studies have shown that the supplements lower triglyceride levels, fish oil supplements tend to increase LDL cholesterol, often referred to as the bad cholesterol. The increase was significant, especially in those taking the highest doses.7, 8
Consuming fish oil (or vitamin E) also does not prevent secondary coronary heart disease (subsequent episodes following non-fatal heart attacks or strokes). Researchers did admit that important questions still remain about the benefits of plant sources of EFAs, but they were definite about the promotion of fish oil capsules for the prevention of further episodes.9
- 1Song and Miyazawa. 2001. “Enhanced level of n-3 fatty acid in membrane phospholipids induces lipid peroxidations in rats fed dietary docosahexaenoic acid oil.” Atherosclerosis 155:9-18.
- 2Simopoulos. 2002. “Omega-3 fatty acids in wild plants, nuts, and seeds.” Asia Pacific Journal of Clinical Nutrition.
- 3Song, Fujimoto, and Miyazawa. 2002. “Polyunsaturated (n-3) fatty acids susceptible to peroxidation are increased in plasma and tissue lipids of rats fed docosahexaenoic acid DHA-containing oils.” American Journal of Clinical Nutrition 130:3028-33.
- 4Thies, Caron, Powel, Yagoob, Newsholme, and Calder. 2001. “Dietary supplementation with eiosapentaenoic acid, but not with other long-chain n-3 or n-6 polyunsaturated fatty acids, decreases natural killer cell activity in healthy subjects aged >55 years.” American Journal of Clinical Nutrition 73:539-48.
- 5“Fish oil poses problems, researchers charge – Agricultural Research Human Nutrition Center on Aging at Tufts University; Food and Drug Administration unconvinced of health benefits.” Nutrition Health Review, Spring 1991.
- 6“Fish Oil.” UC Berkeley Wellness Letter, November 2003.
- 7Friedberg, Janssen, Heine, and Grobbee. 1998. “Fish oil and glycemic control in diabetes.” Diabetes Care 21(4):494-500.
- 8Montori, Farmer, Wollan, and Dinneen. 2000. “Fish oil supplementation in type 2 diabetes.” Diabetes Care 23(9):1407-15.
- 9Stone. 2000. “The Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto Miocardio (GISSI)-Prevenzione Trial on Fish Oil and Vitamin E Supplementation in Myocardial Infarction Survivors.” Current Cardiology Reports 2(5):445-51.
This page was researched in November 2005.