What Is Krill Oil? How Does It Differ from Fish Oil, and What Are Its Health Effects?

Krill oilhas gained popularity in recent years as an alternative omega-3 source to traditional fish oil. Derived from krill, small shrimp-like crustaceans, this oil is marketed with many benefits, from protecting cardiovascular health and reducing joint pain to supporting brain function and providing antioxidant effects. But what does scientific research say about krill oil? In this article, you will find answers to questions such as what krill oil is, how it is produced, how it differs from fish oil, whether its health effects are scientifically proven, how it is used, its side effects, and who should avoid it .

What Is Krill Oil? Its Source and Production

Antarctic krill (Euphausia superba). Krill oil is a source of omega-3 fatty acids derived from these small crustaceans living in cold ocean waters.

Krillis a small, reddish, shrimp-like crustacean measuring 1–6 cm that lives in cold ocean waters around the Arctic and Antarctica. In Norwegian, the word "krill" means "whale food" ; indeed, some large marine animals and fish, especially whales, feed on swarms of krill. Antarctic krill (Euphausia superba) forms one of the world's ocean populations with the highest biomass, reaching a collective weight of hundreds of millions of tons.

Krill oilis an oil obtained mainly from Antarctic krill. After krill are caught using large nets and sustainable fishing methods, they are processed to extract their oil. The crude oil is then purified and concentrated. Krill oil's distinctive red color comes from a pigment called astaxanthin. Commercial krill oil is generally offered as a supplement in soft gelatin capsules. This oil is particularly known for being rich in omega-3 fatty acids and is known for this; for "people who dislike the smell or taste of fish" it is marketed as an alternative omega-3 source.

What Are Krill Oil's Composition and Nutritional Value?

Krill oil's nutritional profile includes certain features that distinguish it from other omega-3 sources. Its main components are polyunsaturated fatty acids (PUFA) , particularly from the omega-3 family, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Krill oil also contains a powerful antioxidant, astaxanthin and phosphatidylcholine (a choline-containing phospholipid). The average fatty acid and lipid composition of 100 grams of krill oil is provided below:

The table above shows how rich an omega-3 source krill oil is. Approximately, in 100 grams of krill oil, 25 grams of omega-3 fatty acids are present, mostly EPA and DHA. This proportion is similar to the omega-3 content of fish oil. Also notable is that krill oil contains around 43% fat in phospholipid form. The storage of omega-3 fatty acids in phospholipid formis a distinctive feature of krill oil, since omega-3s in fish oil are mostly in triglyceride form. The phospholipid structure may facilitate the passage of krill oil's omega-3s through the intestinal wall and increase absorption — a proposed bioavailability advantage.

In addition, krill oil is red because it contains the pigment astaxanthin . Astaxanthin is a powerful carotenoid with both antioxidant and anti-inflammatory properties. It protects the delicate omega-3 fatty acids in krill oil against oxidative damage and may also have beneficial effects in the body. For example, astaxanthin is reported to inhibit oxidation of polyunsaturated fats in cell membranes, reduce the harmful effects of UV rays on skin, suppress excessive inflammatory responses, and potentially play a protective role against various chronic diseases. Another component distinguishing krill oil from fish oil supplements is choline. Through its phosphatidylcholine structure, krill oil supplies the body with choline, a nutrient that may be conditionally "essential" and plays important roles in nerve transmission (acetylcholine), cell membrane structure and homocysteine metabolism. Thus, apart from omega-3, krill oil also gains value as a dietary supplement providing antioxidants and choline .

What Are the Differences and Advantages of Krill Oil Compared with Fish Oil?

Krill oil is often compared with fish oil because both provide omega-3 fatty acids (EPA/DHA). However, there are important differences in their sources and chemical properties. The table below summarizes the main differences between krill oil and fish oil:

As these differences show, krill oil particularly differs structurally from fish oil. Since its omega-3s are in phospholipid form, their absorption in the body is thought to be more efficient. Indeed, some studies have shown that, when equal amounts of EPA and DHA are given, krill oil's omega-3s may have higher bioavailability than fish oil (according to some findings, approximately 1.5 times higher). For example, a study of 117 healthy individuals lasting 7 weeks found that plasma EPA/DHA levels increased equally in the krill oil group and the fish oil group despite a lower dose of omega-3 in the former, and reported that krill oil might have 59% higher bioavailability. However, not all studies agree; some found no marked difference in omega-3 absorption between krill and fish oil. Thus, whether krill oil produces similar effects at lower doses remains scientifically unresolved.

Another advantage of krill oil is that, thanks to its astaxanthin content, it is more resistant to oxidation . Because fish oils contain no antioxidants, they are more prone to oxidizing and deteriorating (becoming rancid) over time, whereas astaxanthin naturally protects krill oil. This helps krill oil supplements remain more stable on the shelf and exert an antioxidant effect in the body. Krill oil also supplies some choline , which fish oils do not — choline is important for liver health, brain function and cell membrane integrity.

Krill oil is also said to have a practical advantage in taste and use: users report that its capsules do not cause fish reflux (fishy burps) and have a more neutral taste. The strong fishy flavor experienced by some fish oil users is less noticeable with krill oil. This makes it easier to use.

In environmental and economic terms, there are also differences between krill oil and fish oil. Since krill is a planktonic organism near the bottom of the food chain, its accumulation of heavy metals (such as mercury) and toxic substances is considerably lower than that of fish. In theory, this could make krill oil a "purer" omega-3 source. Indeed, although heavy metals such as mercury are generally removed from fish oils, this risk is lower to begin with in krill oil. However, a 2014 analysis pointed out that some commercial krill oil products may contain moderate levels of persistent organic pollutants (industrial toxins). Therefore, quality standards matter for both oils.

Economically, because krill oil production is more labor-intensive and limited, it is more expensive than fish oil. For example, krill oil capsules in online markets generally sell at a higher price than fish oil capsules with equivalent doses. Antarctic krill harvesting is also limited by international quotas; ecosystem balance and restricted supply keep production below a certain scale. Fish oil, by contrast, is also obtained from by-products of fish such as tuna, mackerel and anchovies and is produced on a large scale, making it a more accessible and affordable supplement.

Finally, fish oil has been researched far more extensively, whereas publications on krill oil are limited. The literature includes tens of thousands of studies on fish oil , whereas the number of publications on krill oil is a very small fraction of that. This indicates that more studies are needed to fully understand krill oil's potential benefits and risks.

What Are the Benefits and Health Effects of Krill Oil?

Krill oil's health effects are largely thought to arise from its omega-3 (EPA/DHA) and astaxanthin content. Marketing claims suggest that krill oil may offer a broad range of benefits, such as protecting cardiovascular health, lowering cholesterol, reducing joint inflammation (arthritis), supporting brain and mental health, improving menstrual (PMS) symptoms and even preventing cancer . But does scientific research support these claims? Here are the scientific findings on krill oil's possible benefits:

Does Krill Oil Support Heart Health? Does It Lower Cholesterol?

Omega-3 fatty acids are generally known for their positive effects on cardiovascular health. Some studies have examined krill oil in this context, particularly its effects on blood fats (lipid profile). A meta-analysis conducted in 2017analyzed 7 clinical trials (662 participants in total) evaluating krill oil supplementation's effects on blood lipids. According to its results, krill oil use provided LDL ("bad" cholesterol) and triglyceride levels, compared with placebo, with a significant reduction . A fall in total cholesterol was also observed, but this change was not statistically significant. Thus, krill oil appears to show potential benefit particularly in reducing bad cholesterol and triglycerides.

Although these findings are promising, an important point must be noted: these studies generally measure short-term biomarker changes (cholesterol, triglyceride levels, etc.). What actually matters, however, is the effect on clinical outcomes such as heart attack and stroke. There is not yet sufficient evidence that krill oil directly prevents cardiovascular events. The American Heart Association (AHA) also states that studies of omega-3 supplements have yielded conflicting results, that the benefit of omega-3 in preventing heart disease is unclear, but that taking reasonable doses is generally safe. Therefore, even if krill oil lowers cholesterol, whether this translates into a tangible reduction in heart attack risk is uncertain. Nevertheless, in individuals with high triglycerides or omega-3 deficiency, krill oil supplementation under medical supervision may support heart health.

Some research has also directly compared krill oil and fish oil supplements. Small clinical studies have suggested that krill oil, even when used in smaller amounts than a comparable dose of fish oil, may produce equivalent or greater improvement in cholesterol. However, more studies are needed in this area.

Does Krill Oil Affect Inflammation and Joint Health?

The anti-inflammatory effects of omega-3 fatty acids are well known. The EPA and DHA in krill oil may also help reduce the body's inflammatory response. Astaxanthin also has anti-inflammatory properties. Krill oil has therefore been claimed to be potentially useful in joint conditions such as rheumatoid arthritis or osteoarthritis (joint degeneration) .

Scientifically, only a limited number of krill oil studies exist, but some results are positive. For example, in a small clinical study of patients with osteoarthritis (knee joint degeneration), supplementation for 30 days with 2 grams of krill oil daily produced modest improvements in knee pain, stiffness and function compared with placebo. Krill oil was reported to be safely tolerated and potentially effective in reducing mild-to-moderate osteoarthritis symptoms.

In contrast, another larger study found that krill oil supplementation's effect on pain in knee osteoarthritis was no different from placebo . In this 6-month study of 262 participants, no marked difference in knee pain was detected between those using krill oil and those not using it. Thus, results regarding its effects on joint health are inconsistent.

Overall, there are some data showing that krill oil can reduce the body's CRP and similar inflammatory markers . Studies in people with mildly elevated blood fats and joint complaints have reported reduced inflammatory cytokine levels with krill oil. For example, one study found that supplementation reduced the inflammatory marker CRP by 19%, while the placebo group showed a 16% increase (2007, Deutsch et al.). These findings suggest that krill oil may have anti-inflammatory effects. Nevertheless, evidence remains insufficient regarding its role particularly in chronic joint diseases, and more comprehensive research is needed.

Does Krill Oil Improve Brain and Mental Health?

Approximately 60% of the human brain's dry weight is fat, and omega-3 fatty acids are critically important for brain health. DHA is abundant in brain tissue and can influence cognitive function and mood. Epidemiological studies suggest that fish and fish oil consumption may reduce depression risk. Some research proposes that omega-3 supplements may help alleviate depressive symptoms. In this context, krill oil has also been claimed to have positive effects on depression, anxiety or cognitive functions .

However, specifically for krill oil, there is not yet strong evidence regarding brain and mental health . Preliminary research suggests a possible relationship between omega-3 levels and depression, but no high-quality clinical trial confirms krill oil's role in treating depression. For example, no published study has proved a marked improvement in patients given krill oil alongside treatment for major depression. It is therefore too early to say "krill oil is good for depression."

Similarly, memory, concentration or Alzheimer's disease have been studied only to a limited extent with krill oil. Although some evidence suggests that omega-3s generally may slow cognitive decline or support learning in children, whether krill oil has a greater effect than fish oil is unclear.

In summary, no clear evidence-based benefit has yet been established for krill oil's effects on mental health and neurological functions . Although it provides general support in people with omega-3 deficiency, recommending it specifically for anxiety or depression requires more research.

What Is Krill Oil's Role in Cancer and Other Diseases?

Some data suggest that omega-3 fatty acids may affect cancer risk. For example, some studies propose that high omega-3 intake may slightly reduce breast cancer risk but potentially increase prostate cancer risk. These conflicting effects illustrate the complex role of omega-3s in cancer biology, and the subject remains under investigation.

Specifically for krill oil, although recommendations exist for cancer prevention or support during treatment , scientific evidence is extremely limited. Controlled clinical studies directly evaluating its use in cancer patients are almost nonexistent. There is therefore no evidence that krill oil has a therapeutic effect in any cancer type.

Instead, an issue requiring attention in cancer is the potential drawback of fish/krill oil supplementation in patients receiving chemotherapy. Some research in 2015 suggested that particular fatty acids in fish oil (such as a fatty acid called 16:4(n-3)) might trigger resistance to chemotherapy drugs in tumor cells. Consequently, some oncologists advise patients undergoing chemotherapy not to take omega-3 supplements (fish or krill oil). Indeed, experts such as Prof. Dr. Mustafa Özdoğan do not recommend these supplements in patients receiving cancer treatment because of potential interactions.

Beyond this, krill oil's effects on diabetes, metabolic syndrome or premenstrual syndrome (PMS) have also been investigated. Animal studies suggest it may improve glucose metabolism and reduce insulin resistance. For example, krill oil supplementation reduced liver fat accumulation and insulin resistance in mice (2014, Nutr Metab (Lond) journal). In humans, a small study comparing krill oil and fish oil for relieving PMS symptoms reported greater improvements in menstrual cramps and mood swings in the krill oil group (2003, Sampalis et al.). Although these individual findings are interesting, more comprehensive, reproducible research is needed to confirm the benefits.

In conclusion, krill oil may potentially benefit heart health, inflammation and certain other areas. However, many of these benefits are already claimed for fish oil, and whether krill oil is superior to fish oil in these areas is unclear. Given the limited research, cautious optimism should be adopted regarding its health effects. Although useful as an omega-3 supplement, it should not be regarded as a miracle product.

Uses and Dosage of Krill Oil

Krill oil supplementationis primarily used to supply omega-3 fatty acids. As with fish oil, it is consumed for the following purposes:

• Cholesterol and Triglyceride Control: As support for reducing high cholesterol or triglycerides (particularly to benefit from omega-3s' cardiovascular effects).
• Supporting Cardiovascular Health: For those at risk of coronary heart disease or wishing to protect heart health.
• Joint and Rheumatic Complaints: For people with joint pain and stiffness from conditions such as osteoarthritis or rheumatoid arthritis, to benefit from omega-3s' anti-inflammatory effects.
• Brain and Eye Health: Because DHA is important for brain and retinal development, to support a baby's brain-eye development during pregnancy (with medical approval) or preserve cognitive functions in older age.
• Premenstrual Syndrome (PMS): Some women try krill oil to relieve premenstrual symptoms (pain, mood changes).
• General Well-being: People who do not eat fish or have low omega-3 intake may turn to krill oil for immune and general health support.

Krill oil is generally sold as softgel capsules . A typical capsule may contain between 500 mg and 1000 mg (1 gram) of oil. Daily dosage recommended by manufacturers is generally 1-3 grams of krill oil. Scientific studies have also used doses of 1-3 g daily. For example, 1-gram capsules taken as 2 capsules (total 2 g/day) are common.

Research reports that, for therapeutic effects, using krill oil in the range of 1 – 3 grams/day appears safe. However, exceeding 3 grams daily is not recommended, since high omega-3 intake can cause gastrointestinal problems (such as indigestion and diarrhea) in some people. The European Food Safety Authority (EFSA), based on long-term human studies, reported that 1 gram of omega-3 daily is both safe and may provide benefits to general health. Therefore, in most cases, 1-2 grams of krill oil daily can be considered an adequate and safe dosage range.

Krill oil can be taken with meals. Absorption and tolerability are generally better with food. As with fish oil, capsules should be swallowed with water and the recommended dose should not be exceeded.

If you are vegetarian or vegan , krill oil will not be suitable (it is animal-derived). Plant-based omega-3 sources such as algal oil may be alternatives.

Finally, as with any dietary supplement, consulting a healthcare professional before starting krill oil is best. Particularly if you are considering it for a specific health problem, your doctor can determine the appropriate dose and duration.

What Are Krill Oil's Side Effects and Harms?

In general, krill oil is considered a safe supplement and is well tolerated by most people. However, being "natural" does not mean it is completely free of side effects. In clinical studies, approximately 5% of krill oil users experienced some side effects . These mostly mild side effects include:

• Digestive System: Heartburn, reflux (less frequent than with fish oil), nausea, indigestion or loose stools/diarrhea. Particularly at high doses (>3 g/day), such gastrointestinal disturbances may occur.
• Allergic Reaction: Krill belongs to the shellfish category. In people allergic to shellfish (shrimp, crab, lobster, etc.), krill oil can cause serious allergic reactions. If symptoms such as rash, itching, swelling of the face-tongue-throat or shortness of breath develop, immediate medical help should be sought. People with seafood allergies should therefore strictly avoid krill oil.
• Bleeding Risk: Omega-3 fatty acids may, at high doses, have a blood-thinning effect. This issue, also applicable to fish oil, should be considered with krill oil. Particularly in people taking anticoagulant (blood-thinning) medication, uncontrolled omega-3 supplementation may increase bleeding risk. Rarely, symptoms such as nosebleeds and easy bruising have been reported in krill oil users. Stopping omega-3 supplementation before surgery is also recommended; at least 2 weeks before surgery krill oil should be stopped to help prevent possible excessive bleeding.
• Other Possible Effects: Some users have reported headaches or a fish-like taste after taking krill oil, but these are rare. Another rare effect may be a mild fall in blood pressure in overdose or sensitive individuals (due to omega-3s' antihypertensive effect).

Because long-term data are limited, caution is warranted about uninterrupted use for years. As with fish oil, krill oil does not cause vitamin A and vitamin D accumulation in the body (because it is not fish liver oil and does not contain large amounts of these vitamins). However, persistent organic pollutants are a concern; as mentioned above, these environmental toxins detected in some products may pose health risks with prolonged excessive consumption. Choosing quality-controlled products from reliable brands and staying within recommended doses is therefore important.

If you experience an unexpected effect while taking krill oil (such as palpitations, severe dizziness or yellowing of the skin), it would be appropriate to stop using it and consult a doctor. Although considered safe for the general population, remember that individual differences may occur, as with any supplement.

Who Should Not Use Krill Oil?

Although krill oil may be a beneficial dietary supplement for many people, in some situations it should be avoided or at least not used without consulting a doctor:

• People with Seafood Allergies: People allergic to seafood such as shrimp, crab or oysters should avoid krill oil. Since krill is also a shellfish, it carries a risk of serious allergic reactions.
• People Taking Blood Thinners: In patients taking warfarin, heparin, newer anticoagulants or high-dose aspirin, omega-3 supplements may increase bleeding risk. Those considering krill oil must consult their doctor and closely monitor clotting values (such as INR).
• People Undergoing Surgery: Krill oil and similar supplements should be stopped before surgery (at least 2 weeks beforehand) to prevent excessive bleeding during the operation. If major surgery is planned, tell your doctor about all supplements, including krill oil, and follow their advice.
• Pregnant and Breastfeeding Women: Omega-3 is known to benefit a baby's development during pregnancy and breastfeeding. Doctors may generally recommend fish oil or algal oil supplements particularly high in DHA . Krill oil may theoretically be beneficial, but because it has not been specifically studied in pregnant women, there are no clear safety data. Therefore, pregnant or breastfeeding mothers are not advised to take krill oil without medical approval. If the doctor considers it appropriate, they may prefer krill oil because of its low heavy metal risk, such as mercury; however, dose and duration must be entirely a medical decision.
• Children: Omega-3 supplementation is generally recommended in children if fish intake is low, but products used are usually fish oil- or algal oil-derived, with child-specific doses. Comprehensive research on krill oil in children is lacking. Since its safety is unestablished particularly for young children, pediatric supplementation should only be used after consulting a doctor.
• People Receiving Active Cancer Treatment: As discussed above, omega-3 supplements during cancer treatment (chemotherapy, radiotherapy) are controversial. Some oncologists advise against supplements such as fish/krill oil during treatment because of their potential to cause drug resistance . Oncology patients should therefore not use krill oil without consulting their own doctor.
• People with Liver Disease: High-dose fat supplements (including fish oil) may cause problems in people with severe liver disease or a history of pancreatitis. Although the krill oil dose is relatively low, caution is required, and it should not be started without medical supervision.

In summary, krill oil may not be suitable for everyone. Particularly people with existing illnesses or regular medications should consult healthcare professionals before starting it. Dietary supplements never replace a balanced, healthy diet. Products such as krill or fish oil should be used as "supplements," as their name suggests; omega-3 needs should preferably be met from natural foods (for example, 2 portions of oily fish weekly).

Conclusion

Krill oil is a dietary supplement rich in omega-3 fatty acids EPA and DHA, containing antioxidants such as astaxanthin and offered as an alternative to fish oil. Its different chemical properties (omega-3 in phospholipid form, high EPA ratio, choline content) have been proposed to offer advantages in bioavailability and effect. Although research shows that krill oil can reduce LDL cholesterol and triglycerides and soothe inflammation, regarding overall health benefits, the evidence remains limited . Although generally safe, gastrointestinal side effects and bleeding risk should be considered at high doses. Particularly people with seafood allergies and certain special conditions should avoid krill oil. Finally, the best omega-3 source is fish itself; eating oily fish a few days a week is the healthiest option for meeting omega-3 needs and obtaining other nutrients. Krill or fish oil supplements are secondary options for those unable to eat fish or needing additional support. For healthy days ahead, remember to prioritize a natural, balanced diet over supplements.