Krill Oil

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 Nov 20, 2024.

Clinical Overview

Use

Krill oil is promoted as an alternative to fish oil supplements. However, only limited clinical studies with small sample sizes have been conducted.

Dosing

Dyslipidemia: Krill oil dosages of 500 mg/day to 4 g/day for durations of 4 weeks up to 3 months have been studied. According to a meta-analysis, at least 12 weeks of supplementation is likely needed to see improvement in triglycerides, total cholesterol, and LDL; doses of at least 2 g/day are likely needed for HDL benefit. Krill oil 500 mg capsules commonly contain eicosapentaenoic acid (EPA) 60 mg, docosahexaenoic acid (DHA) 30 mg, and astaxanthin 61 mcg. However, EPA and DHA content of some commercially available krill oil dietary supplements can vary widely from labeled amounts.

Contraindications

Allergy to other crustaceans or shellfish.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

Omega-3 fatty acids, components of krill oil, may exert an antiplatelet action. Krill oil should be used with caution with anticoagulants (eg, warfarin) or antiplatelet agents (eg, aspirin, clopidogrel, prasugrel).

Adverse Reactions

Krill oil appears to be generally well tolerated. Adverse effects include GI symptoms (eg, flatulence, nausea, diarrhea).

Toxicology

Information regarding toxic effects with the use of krill oil is limited.

Source

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.(Burri 2015, FAO 2021, Kwantes 2015)

History

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.(FAO 2021, Gigliotti 2011, Nicol 2003)

Chemistry

Whole krill consist of water (approximately 80%), protein (approximately 15%), lipids (up to 4%), chitin, and carbohydrates. Krill oil contains phospholipids (40%) (particularly phosphatidylcholine), long-chain polyunsaturated fatty acids including EPA and DHA, and 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.(Burri 2015, Cunningham 2012, FAO 2021, Gigliotti 2011, Kwantes 2015)

Uses and Pharmacology

Limited clinical studies with small numbers of participants have been conducted.(Kwantes 2015, Ulven 2015) 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.(Cunningham 2012, Ghasemifard 2015, Köhler 2015, Kwantes 2015, Ramprasath 2015, Salem 2014, Ulven 2015, Yurko-Mauro 2015) Focus has centered on bioavailability, particularly concerning 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 choline (as phosphatidylcholine) and of the carotenoid astaxanthin.(Cicero 2015, Cunningham 2012, Sung 2020, Ulven 2015)

Whereas previous studies have been limited mostly to assessment of methyl ester fatty acid moieties, laboratory advances have allowed for a more detailed description of postprandial incorporation of long-chain n-3 fatty acids across the full plasma lipidome. Acute changes in plasma lipidomes have been reported post-consumption of krill oil or fish oil in which phospholipid species containing n-3 components were significantly increased in plasma. Acutely, krill oil phospholipids were increased equally, if not more, than those from fish oil. In contrast, plasma levels of several n-3 triacyl and diacyl glycerols were significantly lower after krill oil than fish oil consumption.(Sung 2019) Short-term administration produced an increase in plasma EPA (by 35.6%) with 30-day use of krill oil compared to fish oil but not in the other long chain n-3 PUFA moieties (ie, DHA, DPA, arachidonic acid, linoleic acid, alpha-linolenic acid). Other significant differences included higher cholesterol-based lipids and lower phosphatidylserine with krill oil. Overall, 47% of lipid molecular species were altered following supplementation with krill oil or fish oil. Compared to fish oil, krill oil produced a significant increase in 60% of both neutral and polar lipid species and a significant decrease in 40%.(Sung 2020)

For further information regarding uses of omega-3 fatty acids from fish and other sources, see the Omega-3 Fatty Acids monograph.

Antioxidant activity

Animal and in vitro data

Antioxidant activity has been demonstrated in chemical analyses.(Gigliotti 2011, Polotow 2015)

Cancer

In vitro data

Krill oil decreased migration in human colorectal cancer cells via effects on epidermal growth factor signalling.(Jayathilake 2020)

CNS effects

Animal data

Limited studies in rodents suggest improved cognitive function and also antidepressant effects with supplemental krill oil.(Barros 2014, Burri 2015, Wibrand 2013)

Clinical data

A 12-week clinical study compared krill oil 2 g/day with fish oil and placebo and found no effect of krill oil on EPA blood concentrations. Electroencephalogram measures suggested a potential benefit of krill oil on working memory, but the study was too small (N=45) to make recommendations.(Konagai 2013)

The effect of krill oil supplementation on cognitive achievements in 267 adolescents with a low omega-3 index (5% or less) was investigated by the Food2Learn study, a double-blind, randomized, placebo-controlled trial conducted in Dutch second-year high school students. More than half (52%) of the students discontinued the study, with loss of motivation, forgetting, and difficulty swallowing the capsules being the most common reasons for both groups. Data collected after 6 and 12 months of administration of 8 placebo or krill oil capsules/day (daily doses of EPA 520 mg and DHA 280 mg) revealed no predictive association between group allocation or omega-3 index and neurocognitive test scores. Interindividual omega-3 fatty acid plasma responses to krill oil supplementation were highly variable.(van der Wurff 2019)

Diabetes

Animal data

Limited studies in animals have shown reduced plasma glucose at high, but not low, krill oil dosages,(Li 2013) while others reported improved insulin sensitivity and glucose tolerance.(Burri 2015, Skorve 2015)

Clinical data

Limited clinical studies with small numbers of participants have been conducted.(Kwantes 2015, Ulven 2015) A study of patients with type 2 diabetes (N=47) reported improvements in cardiovascular risk factors (endothelial dysfunction and 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.(Lobraico 2015) 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.(Trepanowski 2012) No relevant findings were reported in a trial conducted among overweight/obese men and women (N=76).(Maki 2009) A trial evaluating 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.(Albert 2015) Researchers suggest that the krill oil component, consisting of phospholipid forms of fatty acids, was more likely than the salmon oil component to be responsible for these negative effects.

The American Diabetes Association's updated guidelines on the standards of medical care in diabetes (2021) recommends an individualized medical nutrition therapy program as needed to achieve treatment goals for all people with type 1 or 2 diabetes, prediabetes, and gestational diabetes (level A) with dietary fats supplied by eating foods rich in long-chain omega-3 fatty acids like EPA and DHA to prevent or treat cardiovascular disease (level B).(ADA 2021)

Dry eye disease

Clinical data

A double-blind, randomized, placebo-controlled comparator trial in 60 adults with dry eye syndrome reported some differences in 60- and 90-day outcomes depending on whether omega-3 fatty acid supplementation was given as either fish oil or krill oil. Oral daily EPA and DHA doses were 1,000 mg and 500 mg, respectively, for the fish oil group and 945 mg and 510 mg, respectively, for the krill oil group; olive oil was used as a placebo. Both fish and krill oil significantly improved tear osmolarity, tear film stability, and ocular redness at day 90 compared with placebo; a transient significant improvement in ocular surface staining was observed at day 60 but not at day 90. Krill oil, but not fish oil, significantly improved the ocular surface disease index at day 90 compared with placebo (P=0.02). Krill oil supplementation also significantly reduced the proinflammatory cytokine interleukin 17A (mean reduction, −27 pg/mL versus +46 pg/mL, respectively; P=0.02). Overall, adverse events were similar among the 3 arms. No serious adverse events were reported and no significant changes in intraocular pressure or best-corrected visual acuity occurred.(Deinema 2017)

Dyslipidemia/Cardiovascular effects

Animal data

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 LDL.(Burri 2015, Ferramosca 2012, Ferramosca 2015, Li 2013, Ramsvik 2015) In ovariectomized rats, krill oil supplementation appeared to act on calcium channel–activated vascular contractility.(Sakai 2014)

Clinical data

Limited, generally small, clinical studies have been conducted.(Kwantes 2015, Ulven 2015) A study in patients with type 2 diabetes (N=47) reported improvements in cardiovascular risk factors (endothelial dysfunction and HDL levels).(Lobraico 2015) 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(Trepanowski 2012); similar nonrelevant findings were reported in another trial conducted among overweight/obese men and women (N=76).(Maki 2009) Decreased triglycerides were reported in a larger (N=300) study evaluating a range of krill oil doses (0.5 to 4 g/day for 12 weeks); LDL levels were unaffected.(Berge 2014)

A study in healthy volunteers (body mass index 23.8±3 kg/m²) reported no change in serum triglycerides; however LDL-C was increased after 4 weeks of krill oil supplementation.(Ramprasath 2013) A short-term pilot study (N=17) in young adults (18 to 36 years) showed reductions in triglycerides, VLDL, and chylomicron levels after treatment with krill oil 832.5 mg (EPA to DHA ratio of 1.8:1) for 28 days.(Berge 2015)

A systematic review and meta-analysis of 7 randomized controlled trials in healthy (N=167), dyslipidemic (N=357), and diabetic (N=47) adults determined that administration of krill oil improved lipid parameters, but only when given for 12 weeks or more. Doses ranged from 500 mg/day to 4 g/day for durations of 4 weeks to 3 months; sample sizes ranged from 20 to 267. Although HDL increased significantly independently of duration, improvement was seen only in subgroups of studies using doses of at least 2 g/day (weighted mean difference [WMD], +7.25 mg/dL; P=0.018) whereas triglycerides decreased significantly independently of dose but only with a 12-week or greater supplementation duration (WMD, −17.67 mg/dL; P<0.001). Total cholesterol (WMD, −24.12 mg/dL; P=0.026) and LDL (WMD, −37.14 mg/dL; P=0.009) decreased significantly only in subgroups of studies with supplementation durations of at least 12 weeks. No subgroup data were provided on healthy versus unhealthy participants. A few cases of mild to moderate GI symptoms were reported for krill oil.(Ursoniu 2017)

Inflammation

Animal data

Some studies in rodents suggest that supplementation with krill oil reduces tumor necrosis factor alpha levels and improves clinical signs of arthritis (induced),(Burri 2015, Skorve 2015) while other studies have not demonstrated changes in inflammatory indices.(Burri 2015, Polotow 2015, Vigerust 2013)

Clinical data

Limited clinical studies with small numbers of participants have been conducted.(Kwantes 2015, Ulven 2015) In a study evaluating the effect of krill oil in patients with dysmenorrhea (N=70), fewer analgesics were consumed and improvements in self-assessed symptoms were reported.(Sampalis 2003) In a small 6-week study in healthy young adults (N=37) to evaluate effects of krill oil supplementation on postexercise immune function and performance, some markers of inflammation were affected; however, no effect on exercise performance was found.(Da Boit 2015) Limited studies have been conducted in arthritis, with methodological limitations.(Kwantes 2015)

Osteoarthritis

Clinical data

In a double-blind, randomized, controlled trial in adults with mild knee pain (N=50), administration of krill oil 2 g/day for 4 weeks improved only 2 of 25 subjective symptoms of knee pain compared with placebo. The improvements were in activities of daily living: difficulty putting on socks (P=0.044) and difficulty doing heavy housework (P=0.047). Compared with baseline, significant improvements were reported in 16 and 9 of the 25 subjective measures by patients in the krill oil and placebo groups, respectively. Both groups experienced significant improvements in total knee pain scores in both knees, with no significant differences between groups. Changes in scores controlled for age, sex, weight, smoking, and drinking habits demonstrated significant improvements in pain and stiffness scores as well as range of motion attributed to krill oil but not placebo.(Suzuki 2016)

Dosing

Dyslipidemia: Krill oil dosages of 500 mg/day to 4 g/day for durations of 4 weeks up to 3 months have been studied. According to a meta-analysis, at least 12 weeks of supplementation is likely needed to see improvement in triglycerides, total cholesterol, and LDL; doses of at least 2 g/day are likely needed for HDL benefit.(Berge 2014, Ursoniu 2017)

The 2002 American Heart Association (AHA) scientific statement on fish and fish oil consumption suggests a 1 g daily dose of EPA and DHA for cardioprotection, preferably from oily fish, with supplements considered in consultation with a physician; at least 2 g/day (as supplement capsules) is recommended for triglyceride reduction.(Kris-Etherton 2002) Krill oil is not referred to in either the 2002 or 2013 American College of Cardiology (ACC)/AHA cholesterol guidelines.(Backes 2014, Stone 2014)

Krill oil 500 mg capsules often contain EPA 60 mg, DHA 30 mg, and astaxanthin 61 mcg.(Da Boit 2015) However, the EPA and DHA content of some commercially available krill oil dietary supplements can vary widely from labeled amounts; products may also contain the fatty acid linoleic acid.(Nichols 2014, Salem 2014)

Pregnancy / Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking. See the Omega-3 Fatty Acids monograph for information regarding 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. In a 2007 Cochrane meta-analysis, mean gestation was 2.6 days longer (95% CI, 1.03 to 4.07) in women receiving fish oil supplementation. There was no significant difference for 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).(Secher 2007) 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.(Saccone 2015)

A study in which fish oil supplementation was taken after 22 weeks' gestation suggested an increase in oxidative stress in the plasma at week 30.(Franke 2010) Effects of fish oil on lipids and blood pressure do not appear to be sustained during pregnancy.(Barden 2006)

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 breastfeeding infants.(Jensen 2000, Simmer 2004, Smit 2000)

Interactions

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).(Cicero 2015, Kwantes 2015)

Adverse Reactions

Allergy to other crustaceans or shellfish should be considered a contraindication to the use of krill products.(Kwantes 2015) Adverse effects reported in clinical studies include GI symptoms (eg, flatulence, nausea, diarrhea). However, krill oil appears to be generally well tolerated.(Maki 2009, Salem 2014, Ulven 2015)

The safety and tolerability of krill oil powder was investigated in 35 overweight adults with mild to moderate hypertension in a double-blind, randomized, placebo-controlled trial. After 8 weeks of krill oil powder 4 g/day, heartburn was the only adverse event classified as "probably" related to krill oil. No serious events were reported. Hematological, clinical chemistry, lipid, and blood pressure values were not significantly different between groups. Compared with baseline, mean systolic blood pressure decreased significantly with krill oil (P=0.0057), and mean HDL increased significantly with placebo (+0.09 mmol/L; P=0.0231).(Sarkkinen 2018)

Related/similar drugs

Toxicology

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.(Bengtson Nash 2014, Stone 2014) A study in rats (N=10) given krill oil at twice the 5% no-observed-adverse-effect level for 8 weeks showed increased kidney weights and calcium content, as well as renal calcification and tubule-interstitial injury.(Burri 2015)

References

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