Omega-3 krill oil is a marine-derived dietary supplement extracted from Antarctic krill, containing the omega-3 fatty acids EPA and DHA bound to phospholipids rather than triglycerides. Whilst krill oil is marketed for cardiovascular health, joint support, and general wellbeing, it is classified as a food supplement in the UK, not a medicine, and is not subject to pharmaceutical regulatory standards. Clinical evidence for krill oil remains more limited than for traditional fish oil, and NICE does not recommend omega-3 supplements for cardiovascular disease prevention. Patients considering krill oil should understand its potential benefits, safety considerations, and how it compares to other omega-3 sources.

What Is Omega-3 Krill Oil and How Does It Work?

Omega-3 krill oil is a marine-derived dietary supplement extracted from Antarctic krill (Euphausia superba), small crustaceans that form a crucial part of the ocean food chain. Unlike traditional fish oil, krill oil contains omega-3 fatty acids—primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—bound predominantly to phospholipids rather than triglycerides. This structural difference may influence how the body processes these fatty acids, though any absorption advantage remains uncertain and has not been conclusively demonstrated in clinical studies.

The omega-3 fatty acids in krill oil exert their effects through multiple mechanisms. EPA and DHA are incorporated into cell membranes, where they influence membrane fluidity and cellular signalling pathways. These fatty acids serve as precursors to specialised pro-resolving mediators (SPMs), including resolvins and protectins, which help modulate inflammatory responses. Additionally, omega-3s can influence gene expression related to lipid metabolism and inflammatory pathways.

Krill oil also contains astaxanthin, a carotenoid antioxidant that gives the oil its characteristic red colour. Astaxanthin may provide additional antioxidant protection, though its clinical significance at the concentrations found in krill oil supplements remains under investigation. The phospholipid structure of krill oil omega-3s theoretically allows for integration into cellular membranes, though clinical evidence for superior efficacy compared to other omega-3 forms remains mixed.

Potential cardiovascular effects may include reduction of triglyceride levels, modest effects on cholesterol profiles, and anti-inflammatory actions, though these mechanisms have not consistently translated into proven clinical outcomes. Patients should understand that krill oil is classified as a food supplement in the UK, not a medicine, and is not subject to the same regulatory standards as pharmaceutical products. Any health claims made for krill oil must comply with the UK Nutrition and Health Claims Register.

Health Benefits and Clinical Evidence for Krill Oil

Clinical research into krill oil has explored several potential health benefits, though the evidence base remains more limited compared to traditional fish oil supplements. Cardiovascular health represents the most studied area, with some trials suggesting krill oil may help reduce triglyceride levels and improve lipid profiles. A systematic review published in Nutrition Reviews found that krill oil supplementation could modestly reduce total cholesterol and triglycerides, though effect sizes varied considerably between studies.

For joint health and inflammatory conditions, preliminary evidence suggests krill oil may help reduce markers of inflammation such as C-reactive protein (CRP). Small-scale studies have investigated its potential role in managing symptoms of osteoarthritis and rheumatoid arthritis, with some participants reporting reduced joint pain and stiffness. However, these findings require validation in larger, well-designed trials before definitive conclusions can be drawn.

Cognitive function and mental health have also been areas of interest. Omega-3 fatty acids are essential components of neuronal membranes, and observational studies have linked higher omega-3 intake with reduced risk of cognitive decline. However, evidence is currently insufficient to recommend krill oil for depression, anxiety, or cognitive decline.

It is important to note that NICE does not recommend omega-3 capsules or fish oil for secondary prevention after myocardial infarction, and krill oil is not mentioned in NICE guidance. The only omega-3 therapy endorsed by NICE for cardiovascular risk reduction is prescription icosapent ethyl (Vazkepa) with statin therapy for selected high-risk adults with raised triglycerides (NICE TA805). Krill oil should not be used as a substitute for prescribed cardiovascular medications.

For general health maintenance, some individuals report subjective improvements in skin health, menstrual discomfort, and overall wellbeing, though these claims lack substantial clinical evidence. Healthcare professionals should counsel patients that whilst krill oil appears generally safe, its therapeutic benefits for specific conditions remain incompletely characterised.

Recommended Dosage and How to Take Krill Oil

There is no universally established therapeutic dose for krill oil, as it is not a licensed medicine in the UK. Typical supplement formulations provide between 500 mg and 1,000 mg of krill oil per capsule, containing approximately 120–240 mg of combined EPA and DHA. Most manufacturers recommend 1–2 capsules daily, and patients should not exceed the dosage stated on the product label.

Some research studies have used doses ranging from 1 to 4 grams of krill oil daily, but patients should understand that krill oil is a food supplement and should not be used for cardiovascular risk reduction without medical advice. It should never be substituted for prescribed therapies. When comparing krill oil to fish oil, it is essential to consider the actual EPA and DHA content rather than total oil volume, as krill oil typically contains lower concentrations of omega-3s per gram compared to concentrated fish oil preparations.

Administration guidance suggests taking krill oil with meals to enhance absorption and reduce the likelihood of gastrointestinal discomfort. The phospholipid structure may affect absorption compared to triglyceride-based fish oils, though the clinical significance of this difference remains debated in the literature.

Patients should be advised to:

• Store krill oil in a cool, dark place to prevent oxidation

• Check the expiry date and avoid using oxidised products (which may have a strong fishy odour)

• Swallow capsules whole with water

• Maintain consistent daily dosing for optimal effect

Duration of supplementation should be discussed with a healthcare professional. Omega-3 fatty acids require several weeks to months to achieve steady-state levels in cell membranes, so benefits may not be immediately apparent. Patients considering krill oil for specific health conditions should consult their GP to ensure it is appropriate for their individual circumstances and does not interfere with existing treatments. Those taking anticoagulant medications (particularly warfarin, which requires INR monitoring when starting or stopping omega-3 supplements) or antiplatelet medications require particular caution and medical supervision before commencing omega-3 supplementation.

Side Effects and Safety Considerations

Krill oil is generally well tolerated by most individuals, though several side effects and safety considerations warrant attention. Common adverse effects include mild gastrointestinal symptoms such as nausea, loose stools, bloating, and a fishy aftertaste or burping. These effects are typically dose-dependent and may be minimised by taking the supplement with food or choosing enteric-coated formulations.

Allergic reactions represent an important safety concern. Krill are crustaceans, and individuals with shellfish allergies may experience allergic responses ranging from mild skin reactions to severe anaphylaxis. Patients with known shellfish allergies should avoid krill oil entirely and consider alternative omega-3 sources such as algal oil. Healthcare professionals should specifically enquire about shellfish allergies before recommending krill oil supplements.

The anticoagulant properties of omega-3 fatty acids require careful consideration. High-dose omega-3 supplementation may prolong bleeding time and potentially increase bleeding risk, particularly in patients taking anticoagulants (warfarin, DOACs), antiplatelet agents (aspirin, clopidogrel), or NSAIDs. Patients taking warfarin should have their INR monitored when starting or stopping omega-3 supplements. Whilst clinically significant bleeding events are rare at typical supplement doses, patients should inform their GP and pharmacist about krill oil use, especially before surgical or dental procedures. The MHRA advises caution when combining omega-3 supplements with anticoagulant medications.

Pregnancy and breastfeeding considerations are important. Whilst omega-3 fatty acids are beneficial during pregnancy for foetal neurodevelopment, pregnant women should consult their midwife or GP before taking krill oil supplements. In pregnancy, it's important to avoid fish liver oils (due to vitamin A content) and to seek pregnancy-appropriate products. Concerns about potential contaminants and the lack of specific safety data for krill oil in pregnancy mean that dedicated pregnancy omega-3 supplements or dietary sources may be preferable.

Patients should seek medical advice if they experience:

• Signs of allergic reaction (rash, swelling, difficulty breathing)

• Unusual bleeding or bruising

• Severe or persistent gastrointestinal symptoms

• Any unexpected symptoms after starting supplementation

Suspected adverse reactions to krill oil supplements can be reported via the MHRA Yellow Card Scheme.

Quality and purity vary between manufacturers. Patients should choose products from reputable suppliers that provide third-party testing for contaminants such as heavy metals, PCBs, and oxidation markers. Sustainability certifications (such as MSC) may also be relevant for environmentally conscious consumers.

Krill Oil vs Fish Oil: Key Differences

Understanding the distinctions between krill oil and fish oil helps patients and healthcare professionals make informed decisions about omega-3 supplementation. Molecular structure represents the primary biochemical difference: krill oil omega-3s are predominantly bound to phospholipids, whilst fish oil omega-3s are typically in triglyceride or ethyl ester form (though re-esterified triglyceride forms are also available). This structural difference theoretically influences bioavailability, though any absorption advantage remains uncertain and has not been consistently demonstrated in head-to-head clinical trials.

Omega-3 concentration differs substantially between the two sources. High-quality fish oil supplements can contain 60–90% omega-3 fatty acids by weight, whilst krill oil typically contains 20–30%, though this varies considerably by product. This means patients may need to consume more krill oil capsules to achieve equivalent EPA and DHA intake. When comparing products, healthcare professionals should advise patients to examine the actual EPA and DHA content per serving rather than total oil volume.

Additional components distinguish these supplements. Krill oil contains astaxanthin, a carotenoid antioxidant absent from most fish oils, which may provide additional antioxidant benefits and contribute to the oil's stability. However, the clinical relevance of astaxanthin at the doses present in krill oil supplements has not been definitively established. Fish oil supplements may be fortified with vitamin E as an antioxidant preservative.

Tolerability and palatability are reported to favour krill oil in some consumer experiences. Many users report fewer gastrointestinal side effects and less fishy aftertaste with krill oil compared to fish oil, though these observations are largely anecdotal and individual responses vary considerably.

Cost considerations are significant. Krill oil is typically more expensive per unit of EPA and DHA compared to fish oil, reflecting more complex harvesting and processing. Patients on limited budgets may find fish oil more economical for achieving therapeutic omega-3 doses.

Environmental and sustainability factors differ between sources. Antarctic krill are abundant, but concerns exist about ecosystem impacts of large-scale harvesting. Fish oil sources vary widely in sustainability depending on species and fishing practices. Patients concerned about environmental impact should look for products certified by organisations such as the Marine Stewardship Council.

Clinical evidence is more extensive for fish oil, with decades of research. Krill oil research, whilst growing, remains more limited. It's important to note that clinical outcome evidence is stronger for prescription EPA (icosapent ethyl) than for krill oil. There is no conclusive evidence that krill oil is superior to fish oil for cardiovascular or other health outcomes, and patients should not assume equivalence at similar doses due to concentration differences. Healthcare professionals should base recommendations on individual patient factors, including tolerance, cost, allergies, and specific health goals.

Frequently Asked Questions