Scientific Name(s): Euphausia antarctica., Euphausia australis., Euphausia glacialis., Euphausia murrayi., Euphausia superba.
Common Name(s): Arctic krill oil, Krill, Krill oil
Medically reviewed by Drugs.com. Last updated on May 1, 2019.
Krill oil is promoted as an alternative to fish oil supplements. However, only limited clinical studies with small sample sizes have been conducted.
Most clinical studies have used omega-3 doses of 1 to 2 g/day as krill oil. Krill oil 500 mg capsules commonly contain eicosapentaenoic acid (EPA) 60 mg, docosahexaenoic acid (DHA) 30 mg, and astaxanthin 61 mcg.
Allergy to other crustaceans or shellfish.
Information regarding safety and efficacy in pregnancy and lactation is lacking.
Omega-3 fatty acids may exert an antiplatelet action. Krill oil should be used with caution with anticoagulants (eg, warfarin) or antiplatelet agents (eg, aspirin, clopidogrel, prasugrel).
Krill oil appears to be generally well tolerated. Adverse effects include GI symptoms such as flatulence, nausea, and diarrhea.
Information regarding toxic effects with the use of krill oil is limited.
Krill oil and other krill products are obtained from the crustacean E. superba species, which inhabits the extremely cold southern Antarctic Ocean. Approximately 80 other species of Euphausia exist and are found in the northern Arctic Ocean. Similar to shrimp, the red-colored krill grow to a maximum length of approximately 6 cm and weigh up to 2 g (0.07 oz). Krill feed primarily on phytoplankton.
Krill are believed to constitute the largest biomass in the world. Although the stocks appear to be unaffected by major annual harvesting, ecological concerns exist.1, 2, 3
Krill harvesting provides a source of human food in the form of krill paste and frozen tails. Krill is also used in animal feeds and as bait for fishermen. More recent applications include using chitin and chitosan, which are derived from crustaceans, as well as krill oil in the pharmaceutical, cosmetic, and research industries.1, 4, 5
Whole krill consist of water (approximately 80%), lipids (up to 4%), protein (approximately 15%), chitin, and carbohydrates. Krill oil contains phospholipids (40%), particularly phosphatidylcholine, long-chain polyunsaturated fatty acids including EPA and DHA, the antioxidant astaxanthin (also found in shrimp and crayfish), as well as vitamins A and E and the flavonoid 6,8-di-C-glucosyl luteolin.1, 2, 3, 5, 6
Uses and Pharmacology
Limited clinical studies with small numbers of participants have been conducted to date.3, 7 The distinction between krill oil and fish oils as a source of n-3 fatty acid supplementation has not been fully evaluated, especially when matched for dose and EPA and DHA concentrations.3, 6, 7, 8, 9, 10, 11, 12 Focus has centered on bioavailability, particularly concerning the differences in the molecular structure and storage of the n-3 fatty acids of fish oil and krill oil (stored as triglycerides in fish oil and incorporated into phospholipids in krill oil), the ratio of EPA to DHA, and the relevance of the carotenoid astaxanthin.6, 7, 13
For further information on uses of fish-based omega-3 fatty acids, see the Fish Oils monograph.
Limited studies in rodents suggest improved cognitive functioning and antidepressant effects of supplemental krill oil.2, 14, 15
A clinical study evaluated krill oil 2 g/day over 12 weeks versus fish oil and placebo and found no effect of krill oil on EPA blood concentrations. Electroencephalogram measures suggested a potential benefit of krill oil in working memory, but the study was too small (N = 45) to make recommendations.16
Some limited studies in animals have shown reduced plasma glucose at high, but not low, dosages,17 while others reported improved insulin sensitivity and glucose tolerance.2, 18
Limited clinical studies with small numbers of participants have been conducted.3, 7 A study (N = 47) of patients with type 2 diabetes reported improvements in cardiovascular risk factors (endothelial dysfunction and high-density lipoprotein [HDL] levels) and reduced insulin resistance (as measured by blood peptide C levels and homeostatic assessment model algorithm scores) among patients given 2 g/day of supplemental krill oil for 4 weeks.19 However, a study evaluating the effects of krill oil in addition to a 21-day vegan diet found no specific effect of krill oil on outcome measures such as fasting blood glucose, insulin levels, and insulin resistance.20 No relevant findings were reported in a trial conducted among overweight/obese men and women (N = 76).21 A trial of a krill and salmon oil blend (5 g/day) administered for 8 weeks to overweight men reported decreased insulin sensitivity compared with that of the control group, which received canola oil capsules.22 Researchers suggest that the krill oil component, consisting of phospholipid forms of the fatty acids, was more likely than the salmon oil component to be responsible for these negative effects.
In most animal studies, rodents fed a high-fat diet supplemented with krill oil showed reductions in total cholesterol, triacylglycerol, and HDL levels and increased low-density lipoprotein (LDL).2, 17, 23, 24, 25 In ovariectomized rats, krill oil supplementation appeared to act on calcium-channel–activated vascular contractility.26
Limited, generally small, clinical studies have been conducted.3, 7 A study (N = 47) conducted among patients with type 2 diabetes reported improvements in cardiovascular risk factors (endothelial dysfunction and HDL levels).19 However, a study evaluating the effects of krill oil in addition to a 21-day vegan diet found no specific effect of krill oil on outcome measures such as dyslipidemia, systolic blood pressure, or body weight;20 similar nonrelevant findings were reported in another trial conducted among overweight/obese men and women (N = 76).21 Decreased triglycerides were reported in a larger (N = 300) study evaluating a range of doses of krill oil (0.5 to 4 g/day for 12 weeks); LDL levels were unaffected.27 A study in healthy volunteers (body mass index 23.8 ± 3 kg/m2) reported no change in serum triglycerides but did report increased LDL-C after 4 weeks of krill oil supplementation.28 A short-term pilot study (N = 17) in young adults (18 to 36 years) found reductions in triglycerides, very low–density lipoprotein, and chylomicron levels after treatment with krill oil 832.5 mg (EPA to DHA ratio of 1.8:1) for 28 days.29 Only abstract information is available for the largest trial to date: 288 subjects received various doses of a krill oil extract (CaPre) for 8 weeks, with the control group receiving standard of care treatment.30 At 4 weeks, triglyceride levels were reduced significantly in the 1, 2, and 4 g/day groups (−16%, −13%, and −18%), while at 8 weeks, reductions were significant in the 1 and 4 g/day groups (−16% and −14%).
Some studies in rodents suggest that supplementation with krill oil reduces tumor necrosis factor-alpha levels and improves clinical signs of arthritis (induced),2, 18 while other studies have not found changes in inflammatory indices.2, 31, 32
Limited clinical studies with small numbers of participants have been conducted.3, 7 In a study (N = 70) evaluating the effect of krill oil in dysmenorrhea, fewer analgesics were consumed and improvements in self-assessed symptoms were reported.33 In a small (N = 37) 6-week study, some markers of inflammation were affected by krill oil supplementation in healthy young adults; however, no effect on exercise performance was found.34 Limited studies have been conducted in arthritis, with methodological limitations.3
Krill contains hydrolytic enzymes, which are being investigated for potential applications (eg, as chemonucleolytic agents and in debriding necrotic wounds).4 Antioxidant activity has been demonstrated in chemical analyses.5, 31
Most clinical studies have used omega-3 doses of 1 to 2 g/day as krill oil.19, 20, 27, 34
The 2002 American Heart Association (AHA) statement on fish and fish oil consumption suggests a 1 g daily dose of EPA and DHA for cardioprotection and at least 2 g/day for triglyceride reduction.35 Krill oil is not referred to in either the 2002 or 2013 American College of Cardiology (ACC)/AHA cholesterol guidelines.36, 37
Krill oil 500 mg capsules often contain EPA 60 mg, DHA 30 mg, and astaxanthin 61 mcg.34 However, the EPA and DHA content of some commercially available krill oil dietary supplements has been found to vary widely from labeled amounts; products may also contain the fatty acid linoleic acid.10, 38
Pregnancy / Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking. See Fish Oil monograph for information on the benefits of omega fatty acids in pregnancy.
Omega-3 fatty acids may prevent preterm birth via delayed induction of labor and cervical ripening through the inhibition of prostaglandin F2-alpha and E2 production, and by relaxation of the myometrium. A 2007 Cochrane meta-analysis found that mean gestation was 2.6 days longer (95% confidence interval [CI], 1.03 to 4.07) in women who took fish oil supplementation. No significant difference was found for the relative risk (RR) of birth before 37 weeks, while a significant decrease in the risk of birth before 34 weeks' gestation was found (RR, 0.69; 95% CI, 0.5 to 0.99).39 A 2015 meta-analysis of randomized clinical trials (N = 3,854) in women carrying singleton gestations without prior preterm birth found no significant effect of omega-3 supplementation (total daily dose range, 650 to 3,000+ mg of EPA plus DHA; 200 to 500 mg of DHA monotherapy) on rate of preterm birth before 37 weeks compared with controls. However, in a subgroup analysis in women who received EPA plus DHA, mean birth weight was significantly higher (mean difference, 51.18 g). Additionally, perinatal death rate was lower in women receiving omega-3 before 21 weeks of gestation compared with controls.40
A study in which fish oil supplementation was taken after 22 weeks suggested an increase in oxidative stress in the plasma at week 30.41 Effects of fish oil on lipids and blood pressure do not appear to be sustained during pregnancy.42
While evidence indicates that the DHA and EPA composition of breast milk is affected by fish oil supplementation, there is little evidence to support benefit in the breast-feeding infant.43, 44, 45
Omega-3 fatty acids may exert an antiplatelet action. Krill oil should be used with caution with anticoagulants (eg, warfarin) or antiplatelet agents (eg, aspirin, clopidogrel, prasugrel).3, 13
Allergy to other crustaceans or shellfish should be considered a contraindication to the use of krill products.3 Adverse effects reported in clinical studies include GI symptoms (eg, flatulence, nausea, diarrhea). However, krill oil appears to be generally well tolerated.7, 10, 21
Information regarding toxic effects with the use of krill oil is limited. The presence of persistent organic pollutants in krill oil, although occurring at low levels, has been documented.37, 46 A study in rats (N = 10) given krill oil at twice the 5% no observed adverse effects level for 8 weeks showed increased kidney weights and calcium content, as well as renal calcification and tubule-interstitial injury.2
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8. Ghasemifard S, Hermon K, Turchini GM, Sinclair AJ. Metabolic fate (absorption, β-oxidation and deposition) of long-chain n-3 fatty acids is affected by sex and by the oil source (krill oil or fish oil) in the rat [published online August 3, 2015]. Br J Nutr
9. Köhler A, Sarkkinen E, Tapola N, Niskanen T, Bruheim I. Bioavailability of fatty acids from krill oil, krill meal and fish oil in healthy subjects--a randomized, single-dose, cross-over trial [published online March 15, 2015]. Lipids Health Dis
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12. Ramprasath VR, Eyal I, Zchut S, Shafat I, Jones PJ. Supplementation of krill oil with high phospholipid content increases sum of EPA and DHA in erythrocytes compared with low phospholipid krill oil [published online November 4, 2015]. Lipids Health Dis
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15. Barros MP, Poppe SC, Bondan EF. Neuroprotective properties of the marine carotenoid astaxanthin and omega-3 fatty acids, and perspectives for the natural combination of both in krill oil. Nutrients
16. Konagai C, Yanagimoto K, Hayamizu K, Han L, Tsuji T, Koga Y. Effects of krill oil containing n-3 polyunsaturated fatty acids in phospholipid form on human brain function: a randomized controlled trial in healthy elderly volunteers [published online September 19, 2013]. Clin Interv Aging
17. Li DM, Zhou DY, Zhu BW, et al. Effects of krill oil intake on plasma cholesterol and glucose levels in rats fed a high-cholesterol diet. J Sci Food Agric
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20. Trepanowski JF, Kabir MM, Alleman RJ Jr, Bloomer RJ. A 21-day Daniel fast with or without krill oil supplementation improves anthropometric parameters and the cardiometabolic profile in men and women. Nutr Metab (Lond)
21. Maki KC, Reeves MS, Farmer M, et al. Krill oil supplementation increases plasma concentrations of eicosapentaenoic and docosahexaenoic acids in overweight and obese men and women. Nutr Res
22. Albert BB, Derraik JG, Brennan CM, et al. Supplementation with a blend of krill and salmon oil is associated with increased metabolic risk in overweight men [published online May 27, 2015]. Am J Clin Nutr
23. Ramsvik MS, Bjorndal B, Bruheim I, Bohov P, Berge RK. A phospholipid-protein complex from krill with antioxidative and immunomodulating properties reduced plasma triacylglycerol and hepatic lipogenesis in rats [published online July 16, 2015]. Mar Drugs
24. Ferramosca A, Conte L, Zara V. A krill oil supplemented diet reduces the activities of the mitochondrial tricarboxylate carrier and of the cytosolic lipogenic enzymes in rats. J Anim Physiol Anim Nutr (Berl)
25. Ferramosca A, Conte A, Zara V. Krill oil ameliorates mitochondrial dysfunctions in rats treated with high-fat diet [published online August 2, 2015]. Biomed Res Int
26. Sakai Y, Hashimoto M, Enkhjargal B, et al. Effects of krill-derived phospholipid-enriched n-3 fatty acids on Ca(2+) regulation system in cerebral arteries from ovariectomized rats. Life Sci
27. Berge K, Musa-Veloso K, Harwood M, Hoem N, Burri L. Krill oil supplementation lowers serum triglycerides without increasing low-density lipoprotein cholesterol in adults with borderline high or high triglyceride levels [published online December 18, 2013]. Nutr Res
28. Ramprasath VR, Eyal I, Zchut S, Jones PJ. Enhanced increase of omega-3 index in healthy individuals with response to 4-week n-3 fatty acid supplementation from krill oil versus fish oil [published online December 5, 2013]. Lipids Health Dis
29. Berge RK, Ramsvik MS, Bohov P, et al. Krill oil reduces plasma triacylglycerol level and improves related lipoprotein particle concentration, fatty acid composition and redox status in healthy young adults - a pilot study [published online December 15, 2015]. Lipids Health Dis
30. Sampalis T, Pesant Y, Elliot T, et al. COLT, Multicenter CaPre open label randomized dose-ranging phase II trial to assess efficacy/safety in patients with mild-high hypertriglyceridemia. Atherosclerosis
31. Polotow TG, Poppe SC, Vardaris CV, et al. Redox status and neuro inflammation indexes in cerebellum and motor cortex of wistar rats supplemented with natural sources of omega-3 fatty acids and astaxanthin: fish oil, krill oil, and algal biomass [published online September 28, 2015]. Mar Drugs
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