How Does Krill Oil Compare With Fish Oil?

Gayle Nicholas Scott, PharmD


March 05, 2012


Is krill oil a better omega-3 supplement than fish oil for heart disease?

Response from Gayle Nicholas Scott, PharmD
Assistant Professor, Eastern Virginia Medical School, Norfolk, Virginia; Clinical Pharmacist, Chesapeake Regional Medical Center, Chesapeake, Virginia

Krill are small, reddish-colored crustaceans similar in appearance to shrimp. Krill are among the most populous of animal species and are a favorite food of whales. Krill also serve as food sources in oceans worldwide for seals, squid, fish, and seabirds. Antarctic krill (Euphausia superba) are used to a small extent as a human food or supplement source.[1] Commercially, krill are used mainly in the manufacture of fish feeds because of high content of the pigment astaxanthin, which gives salmon their pink color.[2]

Similar to fish oil, krill oil is rich in the omega-3 polyunsaturated fatty acids, eicosapentaenoic acid, and docosahexaenoic acid.[1] Omega-3 fatty acids are associated with reduced risk for coronary heart disease mortality and sudden cardiac death. Omega-3 fatty acids may benefit heart health by lowering plasma triglycerides, resting heart rate, and blood pressure; they also seem to have beneficial effects on myocardial filling and efficiency as well as vascular function. Both national and international organizations have developed guidelines for minimum levels of fish or omega-3 fatty acid consumption for the general population.[3]

Krill oil is less well-studied than fish oil as an omega-3 fatty acid supplement for heart disease. The 1 clinical study available, which apparently was sponsored by the maker of Neptune Krill Oil, compared krill oil 1-3 g/day with fish oil 3 g/day and placebo in 120 patients for 3 months. Results showed that krill oil was superior to fish oil and placebo in improving cholesterol and triglyceride levels.[4]

The comparative bioavailability of omega-3 fatty acids from krill vs fish oil is uncertain. Omega-3 fatty acids from fish oils are mainly associated with triglycerides, whereas the omega-3 fatty acids in krill oil are associated with both phospholipids and triglycerides. Phospholipids and triglycerides digest differently, which may affect the bioavailability of omega-3 fatty acids.Preclinical animal research suggests that fish oil is more digestible and more efficiently incorporated into tissue than krill oil[5]; however, preliminary clinical research suggests that krill oil might have better bioavailability than fish oil.[6]

Similar to fish oil, krill oil can cause adverse gastrointestinal effects, such as gas, bloating, nausea, flatulence, diarrhea, constipation, and cramping.[7] Tolerance to fish oil, and possibly krill oil, may be improved by taking the capsule frozen, switching to a different formulation, or taking the capsule with meals or at a different time of day.[3] Despite some advertising claims, there is no credible evidence to show that krill oil is better tolerated than fish oil. Patients who are allergic to shellfish should avoid krill oil because it contains tropomyosin, a major shellfish allergen.[8,9]

Krill oil seems to be safe for up to 3 months of ingestion, although safety and tolerability was not addressed in the clinical study.[4] Long-term safety and the drug interaction profile are unknown. Theoretically, krill oil may increase the risk for bleeding when combined with antithrombotic drugs, such as warfarin.[10]

In summary, fish consumption is better studied than fish or krill oil supplements. Whether fish oil supplements provide all of the cardiovascular benefits of fish consumption is debated. For patients who don't like fish, fish oil supplements are a reasonable alternative.[3] More research is needed to determine whether krill oil is similar to fish or fish oil with regard to cardiovascular benefits.


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