Studies have shown that omega-3 fatty acids from fish and fish oils are beneficial for helping to prevent and treat arrhythmias,1 thrombosis,2 atherosclerosis,3,4 inflammation,5 high blood pressure6 and elevated triglycerides7 and that they improve endothelial function,8 though the mechanisms by which they confer their benefits are not fully understood.
In 2004, the Food and Drug Administration approved a qualified health claim for foods and supplements containing eicosapentaenoic acid and docosahexaenoic acid omega-3 fatty acids.9 The health claim states, "Supportive, but not conclusive, research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease." The United Kingdom recently became the first country outside the United States to grant an omega-3 fish oil health claim.10
Intakes and recommendations
The average intake of total omega-3 fatty acids in the United States is approximately 1.6 g per day (0.7 percent of energy intake), with only 0.1 to 0.2 g coming from EPA and DHA.11 Though no official recommendation has been set for intakes of EPA and DHA, in 2004 the International Society for the Study of Fatty Acids and Lipids developed some guidelines for adequate intakes.12 ISSFAL recommends that healthy adults consume 0.65 g per day of EPA and DHA combined, with a minimum of 0.22 g of EPA and 0.22 g of DHA. ISSFAL also recommends 0.3 g of DHA a day for pregnant and breastfeeding women.
In 2002, the American Heart Association began recommending much larger amounts of fish oil supplements for people with heart disease: 1 gram a day of EPA and DHA combined for people with coronary heart disease and 2 to 4 g a day for those with elevated triglycerides.13 The updated dietary guidelines released earlier this year by the U.S. Department of Agriculture mention for the first time that DHA and EPA from fish are important for reducing the risk of cardiovascular disease, although the USDA did not specify how much DHA and EPA people should consume.14 Concerns have been raised, however, about harmful environmental contaminants, such as mercury, polychlorinated biphenyls, dioxins and other pollutants, that could be present in fish and fish oils. Critics suggest that these contaminants could reduce the cardioprotective effect of the omega-3s, in addition to carrying risks of their own.15
Fish oil alternatives
Researchers are just now beginning to study two major alternative sources of omega-3 fatty acids: krill and algae. Both are found in several supplements. It's argued that krill and algae pose less risk of containing contaminants than other omega-3 sources because they reside at the bottom of the food chain. Fish and fish oils, on the other hand, come from larger fish that are closer to the top of the food chain and thus are more likely to have consumed other contaminated fish. The higher up the food chain the source is, the greater the likelihood of contamination. However, independent tests on several fish oil supplements have not found contamination to be a problem.16,17 Here's a rundown on these two alternative sources of omega-3s.
These tiny, shrimp-like crustaceans are found in abundance in the Antarctic Ocean. They are mainly herbivorous, feeding on the phytoplankton (microscopic suspended plants) of the southern Antarctic. Krill oil is a rich source of omega-3s, containing approximately 30 percent to 40 percent EPA and DHA.19 Because krill are at the lower end of the food chain, and because they come from the less polluted waters of the Antarctic, some think krill are a purer source of omega-3s than fish oil. However, studies show that even krill can contain contaminants.20
Krill actually provide three supplemental compounds in one. In addition to being a good source of omega-3s, they are rich in the antioxidant carotenoid astaxanthin. Astaxanthin, the source of the pink pigment found in salmon and shrimp, has been shown to have 10 times more antioxidant activity than beta-carotene and as much as 1,000 times more than vitamin E.21 It also is a source of alpha-tocopherol (vitamin E) and an unusual derivative, known as marine-derived tocopherol, that may function as a more efficient antioxidant than alpha-tocopherol.22,23 Researchers have suggested that these tocopherols help krill survive in the frigid Arctic waters. Krill are also an unexpected source of the flavonoid luteolin. Scientists believe it may be the first animal source of this flavonoid, as flavonoids are found almost exclusively in plants.
Krill oil differs from other marine oils in that it contains more EPA per gram than standard fish oil capsules (240 mg per gram versus 180 mg per gram in standard fish oil).24 It is also a rich source of phospholipids, containing about 50 percent.25 Regular fish oils are high in triglycerides, not phospholipids. Manufacturers believe that the cold extraction process used to produce krill oil helps maintain the integrity of the phospholipids.
Research with krill oil has shown it is effective in lowering blood lipids.26 A multicenter study in Canada evaluated 120 people who took krill oil at doses of 1 g, 1.5 g, 2 g or 3 g per day; 3 g of fish oil per day (containing 180 mg of EPA and 120 mg of DHA per gram); or a placebo. After three months of treatment, the krill oil reduced total cholesterol and bad low-density lipoprotein cholesterol and triglycerides. Krill oil also increased good high-density lipoprotein cholesterol and was more effective than fish oil in reducing blood glucose, triglycerides and LDL levels. Those receiving 1 g or 1.5 g of krill oil daily had a 13.4 percent and 13.7 percent decrease in total cholesterol, respectively, compared with a 5.9 percent reduction in total cholesterol in people who took fish oil. LDLs were reduced in the krill oil group by 32 percent to 39 percent, compared with only 4.6 percent in those receiving fish oil. And while HDL levels of those who took fish oil increased only 4.2 percent, those taking krill oil experienced a 43 percent to 59 percent increase.
In one recent study, krill oil was more effective than fish oil in improving the emotional and psychological symptoms of premenstrual syndrome over a three-month treatment period.27 In the study, 70 women diagnosed with PMS were given either 2 g of krill oil or 2 g of fish oil containing 18 percent EPA and 12 percent DHA. (There was no control group.) The researchers suggested that the effectiveness of krill oil on PMS may be the result of modulating effects on neurotransmitters, which they credited to the synergistic effects of omega-3s and phospholipids. No such benefit was observed with regular fish oil supplements. One manufacturer of omega-3 supplements with krill oil claims that the phospholipid content of krill oil allows the omega-3s to pass through the blood-brain barrier with ease, so benefits are provided more readily, but this is speculation.28
Another human study, in which participants ate krill meat, showed that the krill had an aspirin-like effect on blood platelet function.29 Results of at least one animal study have suggested that krill oil may also delay the onset and progression of autoimmune disease, though this has yet to be proven in humans.30
Algae are one type of a larger group of microbes called protists. Protozoans and slime molds also fall into this category. Crypthecodinium cohnil and Schizochytrium are two strains of algae used as a source for supplemental omega-3s. They are typically grown in fermenters under controlled conditions. The algae are dried and the oil extracted for use in supplements. Because of the controlled growing conditions, oil from the algae is thought to be free of contaminants. Omega-3 fats from algae are classified as generally recognized as safe by the FDA, and can be used to fortify foods.
Unlike fish oil or krill oil, which contain both EPA and DHA, oil from algae contains only DHA. The body is able to retroconvert some DHA back to EPA, but diet is the main source of EPA.31 However, research suggests that DHA may be the more critical of the two omega-3s for certain health benefits, especially for infants. DHA is important for normal development of the brain and retina in fetuses and babies. It is often added to infant formulas. Breast milk contains only DHA, not EPA. The body can manufacture some DHA from the fatty acid alpha-linolenic acid, found in foods like flaxseed and walnuts, but the process is inefficient. DHA from algae sources is currently used to enrich eggs, some nutrition bars and milk alternatives.
DHA from algae has been the subject of many more studies than krill oil, though not all have had positive results. Research suggests it is helpful in improving immune function parameters and treating depression.32 And most recently, DHA from algae was more effective in suppressing the growth of colon cancer cells in mice than EPA,33 resulting in a 90 percent reduction in tumor growth compared with a 66 percent reduction in animals receiving fish oil. Generally, however, when used alone, DHA from algae has not been found to be as effective in reducing platelet aggregation or lowering blood cholesterol as combinations of EPA and DHA from fish oils.34,35 Some studies have linked depression with reduced blood levels of omega-3 fatty acids,36,37 but supplementation with DHA alone has not proven to be effective as a treatment.38 Recent research suggests that depression may be related more to an excess of omega-6 fatty acids in the diet than to a lack of omega-3s.39
The bottom line
Both krill and algae are promising alternative sources for omega-3s. While most fish oil supplements have not been found to contain pollutants, krill and algae may pose less risk of contamination than traditional fish oil supplements.
Aside from the issue of contaminants, these alternative omega-3 sources each offer their own advantages. In addition to being a rich source of DHA and EPA, krill oil provides astaxanthin, a potent antioxidant. It also provides unique forms of other antioxidants, including tocopherols and the flavonoid luteolin. Algae, on the other hand, provides the most concentrated source of DHA and is grown under controlled conditions, greatly reducing if not eliminating the risk of contamination. As an added bonus for vegetarians, DHA supplements made from algae are currently the only nonanimal source of DHA available.
Densie Webb is a freelance writer and industry consultant based in Austin, Texas. She is coauthor of The Dish on Eating Healthy and Being Fabulous! (Atria, 2004).
Natural Foods Merchandiser volume XXVI/number 8/p. 40, 42, 44
Pros and cons
Advantages: Provides both EPA and DHA; most research on omega-3s has been done with fish oils.
Disadvantages: Some supplements may have a fishy aftertaste; concern exists about contamination of oils that come from larger fish.
Advantages: Provides the carotenoid antioxidant astaxanthin as well as a concentrated source of phospholipids. Less likely to be contaminated because it comes from the waters of the Antarctic.
Disadvantages: Less published research than is available for fish oil.
Advantages: Because it is processed under controlled conditions, there is much less chance of contamination. No fishy aftertaste. An option for vegetarians.
Disadvantages: Provides only DHA.
1. Christensen JH, et al. Effect of fish oil on heart rate variability in survivors of myocardial infarction: a double blind randomized controlled trial. BMJ 1996;312:677-8.
2. Mori TA, et al. Interactions between dietary fat, fish, and fish oils and their effects on platelet function in mean at risk of cardiovascular disease. Arterioscler Throm Vasc Biol 1997;17:279-86.
3. Von Schacky C, et al. The effect of dietary omega-3 fatty acids on coronary atherosclerosis: a randomized, double-blind, placebo-controlled trial. Ann Intern Med 1999;130:554-62.
4. Eritsland J, et al. Effect of dietary supplementation with n-3 fatty acids on coronary artery bypass graft patency. Am J Cardiol 1996;77:31-36.
5. De Caterina R, et al. Fatty acid modulation of endothelial activation. Am J Clin Nutr 2000;71(suppl):S213-23.
6. Geleijnse JM, et al. Blood pressure response to fish oil supplementation: metaregression analysis of randomized trials. J Hypertens 2002;20:1493-99.
7. Burr ML, et al. Effects of changes in fat, fish and fibre intakes on death and myocardial reinfarction:diet and reinfarction trial (DART). Lancet 1989;2:757-61.
8. Ascherio A, et al. Dietary intake of marine n-3 fatty acids, fish intake and the risk of coronary disease among men. N Engl J Med 1995;332:977-82.
9. "FDA Announces Qualified Health Claims for Omega-3 Fatty Acids." Food and Drug Administration. http://www.fda.gov
10. "Generic Health Claim for Omega-3 PUFA and Heart Health." Joint Health Claims Initiative. www.jhci.co.uk
11. Rigby AJ. Omega-3 choices: fish or flax? Today's Dietitian 2004;6(1):37.
12. "Recommendations for Intake of Polyunsaturated Fatty Acids in Healthy Adults." International Society for the Study of Fatty Acids and Lipids. www.issfal.org.uk
13. Kris-Etherton PM, et al. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation 2002;106-2747-57.
14. "USDA Dietary Guidelines for Americans 2005." United States Department of Agriculture. www.health.gov/dietaryguidelines
15. Din JN, et al. Omega 3 fatty acids and cardiovascular disease—fishing for a natural treatment. BMJ 2004;328:30-5.
16. "Product Review: Omega-3 Fatty Acids (EPA and DHA) from Fish/Marine Oils." Consumer Lab. http://www.consumerlab.com
17. "Omega-3 Oil: Fish or Pills?" Consumers Union. www.consumerreports.org
18. "Krill." Australian Antarctic Division. www.aad.gov.au
19. Bustos R, et al. Oxidative stability of carotenoid pigments and polyunsaturated fatty acids in microparticulate diets containing krill oil for nutrition of marine fish larvae. J Food Engin 2003;56:289-93.
20. Chiuchiolo AL, et al. Persistent organic pollutants at the base of the Antarctic marine food web. Environ Sci Technol 2004;38(13):3551-57.
21. Jyonouchi H, et al. Immunomodulating actions of carotenoids: Enhancement of in vivo and in vitro antibody production to T-dependent antigens. Nutr Cancer 1994; 21:47-58.
22. Dunlap WC, et al. Notothenoid fish, krill and phytoplankton from Antarctica contain a vitamin E constituent (alpha-tocomonoenol) functionally associated with cold-water adaptation. Comp Biochem Physiol B 2002;133:299-305.
23. Yamamoto Y, et al. An unusual vitamin E constituent provides antioxidant protection in marine organisms adapted to coldwater environments. Proc Natl Acad Sci USA 2001;98:13144-48.
24. Logan AC. Omega-3 fatty acids and major depression: A primer for the mental health professional. Lipids in Health and Disease 2004;3:25.
25. "Scientific Facts: Bioavailability." Neptune Technologies and Bioresources. www.neptunebiotch.com
26. Bunea R, et al. Evaluation of the effects of Neptune Krill Oil on the clinical Course of hyperlipidemia. Alternative Medicine Review 2004;9(4):420-8.
27. Sampalis F. Evaluation of the effects of Neptune Krill Oil on the management of premenstrual syndrome and dysmenorrhea. Alternative Medicine Review 2003:8(2)171-79.
28. "Marine Omega Omega-3 Supplement with Krill Oil: Product Information Page." Pharmanex. www.pharmanex.com
29. Anon. Nutritional value of Antarctic krill. Bull World Health Org 1995;73:551.
30. Venkatraman JT, et al. Krill oil and its effects on the antioxidant defense system. Lipids 1994;29(8):561-8.
31. "Omega-3." The Fish Foundation. www.fish-foundation.org.uk.
32. Kew S, et al. Effects of oils rich in eicosapentaenoic and docosahexaenoic acids in immune cell composition and function in healthy humans. A J Clin Nutr 2004;79:674-81.
33. Kato T, et al. Influence of omega-3 fatty acids on the growth of human colon carcinoma in nude mice. Cancer Lett 2003;187(1-2):169-77.
34. Nelson GJ, et al. The effect of dietary docosahexaenoic acid on platelet function, platelet fatty acid composition and blood coagulation in humans. Lipids 1997;32:1129-36.
35. Conquer JA, Holub BJ. Supplementation with an algae source of docosahexaenoic acid increases n-3 status and alters risk factors for heart disease in vegetarian subjects. J Nutr 1996;126:3032-9.
36. Frasure-Smith N, et al. Major depression is associated with lower omega-3 fatty acid levels in patients with recent acute coronary syndromes. Biol Psychiatry 2004; 55(9):891-896.
37. Peet M, Stokes C. Omega-3 fatty acids in the treatment of psychiatric disorders. Drugs 2005;65:1051-9.
38. Marangell LB, et al. A double-blind, placebo-controlled study of the omega-3 fatty acid docosahexaenoic acid in the treatment of major depression. Am J Psychiatry 2003;160(5):996-8.
39. Green P, et al. Increased arachidonic acid concentration in the brain of Flinders Sensitive Line rats, an animal model of depression. Journal of Lipid Research 2005;46:1093-6.