Fish oil

Fish oil

A typical fish oil softgel

Fish oil is oil derived from the tissues of oily fish. Fish oils contain the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors of certain eicosanoids that are known to reduce inflammation in the body,[1][2] and have other health benefits. Nonetheless, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes.[3][4][5]

The fish used as sources do not actually produce omega-3 fatty acids, but instead accumulate them by consuming either microalgae or prey fish that have accumulated omega-3 fatty acids, together with a high quantity of antioxidants such as iodide and selenium, from microalgae, where these antioxidants are able to protect the fragile polyunsaturated lipids from peroxidation.[6][7][8]

Fatty predatory fish like sharks, swordfish, tilefish, and albacore tuna may be high in omega-3 fatty acids, but due to their position at the top of the food chain, these species may also accumulate toxic substances through biomagnification. For this reason, the United States Environmental Protection Agency recommends limiting consumption (especially for women of childbearing age) of certain (predatory) fish species (e.g. albacore tuna, shark, king mackerel, tilefish and swordfish) due to high levels of toxic contaminants such as mercury, dioxin, PCBs and chlordane.[9] Fish oil is used as a component in aquaculture feed. More than 50 percent of the world's fish oil used in aquaculture feed is fed to farmed salmon.[10]

Marine and freshwater fish oil vary in contents of

  • International Fish Oil Standards — An World Health Organization and the Council For Responsible Nutrition for purity and concentration.
  • Two newsletters, both quarterly, reviewing recent publications in essential fatty acids. One is written for researchers, the second is for consumers. Industry sponsored, academic contributors.
  • Omega-3 Fatty Acids American Cancer Society. Updated 11 January 2008.

External links

  • FAO (1986) The production of fish meal and oil FAO Fishery Technical Paper 142. ISBN 92-5-102464-2.


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  48. ^ Reviews of Supplements and Health Products ConsumerLab.
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  51. ^ Mercury Levels in Commercial Fish and Shellfish (1990–2010) U.S. Food and Drug Administration. Accessed 25 March 2013.
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  58. ^ Can you overdose on DHA and EPA? DHA/EPA Omega-3 Institute. Retrieved 4 November 2011.
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  64. ^ International Fish Oil Standards.
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  66. ^ "Lawsuit says fish oil supplements contain PCB", San Francisco Chronicle, March 3, 2010.
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See also

Microalgae oil is a vegetarian alternative to fish oil. Supplements produced from microalgae oil provide a balance of omega-3 fatty acids similar to fish oil, with a lower risk of pollutant exposure.[69]

A report by the Harvard Medical School studied five popular brands of fish oil, including Nordic Ultimate, Kirkland and CVS. They found that the brands had "negligible amounts of mercury, suggesting either that mercury is removed during the manufacturing of purified fish oil or that the fish sources used in these commercial preparations are relatively mercury-free."[68]

An analysis based on data from the Norwegian Women and Cancer Study (NOWAC) with regards to the dangers of persistent organic pollutants (POPs) in cod liver came to the conclusion that "in Norwegian women, fish liver consumption was not associated with an increased cancer risk in breast, uterus, or colon. In contrast, a decreased risk for total cancer was found."[67]

[66][65] A March 2010 lawsuit filed by a California environmental group claimed that eight brands of fish oil supplements contained excessive levels of PCB's, including

Fish oil supplements came under scrutiny in 2006, when the Food Standards Agency in the UK and the Food Safety Authority of Ireland reported PCB levels that exceeded the European maximum limits in several fish oil brands,[62][63] which required temporary withdrawal of these brands. To address the concern over contaminated fish oil supplements, the International Fish Oil Standards (IFOS) Program, a third-party testing and accreditation program for fish oil products, was created by Nutrasource Diagnostics Inc. in Guelph, Ontario, Canada.[64]

Consumers of oily fish should be aware of the potential presence of heavy metals and fat-soluble pollutants like PCBs and dioxins, which are known to accumulate up the food chain. After extensive review, researchers from Harvard's School of Public Health in the Journal of the American Medical Association (2006) reported that the benefits of fish intake generally far outweigh the potential risks.

Toxic pollutants

The liver and liver products (such as cod liver oil) of fish and many animals (such as seals and whales) contain omega-3, but also the active form of vitamin A. At high levels, this form of the vitamin can be dangerous (Hypervitaminosis A).[61]


The FDA says it is safe to take up to 3000 mg of omega-3 per day.[58] (This is not the same as 3000 mg of fish oil. A 1000 mg pill typically has only 300 mg of omega-3; 10 such pills would equal 3000 mg of omega-3.) Dyerberg studied healthy Greenland Inuit and found an average intake of 5700 mg of omega-3 EPA per day.[59] According to the European Food Safety Authority's (EFSA) Panel on Dietetic Products, Nutrition and Allergies, supplementation of 5 grams of EPA and DHA combined does not pose a safety concern for adults.[60]

Maximum intake

A 2013 review concluded that that the potential for adverse events amongst older adults taking fish oil "appear mild–moderate at worst and are unlikely to be of clinical significance".[57]


Fish oil preparations that are only available with a doctor's prescription undergo the same FDA regulatory requirements as other prescription pharmaceuticals, with regard to both efficacy and safety.[56]

Prescription fish oil

Fish oil supplements are available as liquids, capsules, and tablets. Some pills are enteric-coated to help prevent indigestion or "fish burps", however; enteric-coated products have the potential to release ingredients too early or late in the digestive process. In 2010 reports that one of 24 fish oil supplements with enteric-coated pill released ingredients prematurely ; claims in its publication that there were problems in results of tests it ordered in 2012.[47] Fish oils are best tolerated when taken with meals, and, if possible, should be taken in equally divided doses throughout the day.


According to independent laboratory tests, the concentrations of EPA and DHA in supplements can vary from between 8 to 80% fish oil content. The concentration depends on the source of the omega-3s, how the oil is processed, and the amounts of other ingredients included in the supplement.[52] A 2012 report claims 4 of 35 fish oil supplements it covered contained less EPA or DHA than was claimed on the label, and 3 of 35 contained more[52] A publication in 2010 claims 3 of 24 fish oil supplements it covered contained less EPA and/or DHA than was claimed on the label.[47] However, the bioavailability of EPA and DHA from both capsular and emulsified fish oils has been shown to be high.[55]

The American Heart Association recommends 250–500 mg/day of EPA and DHA.[54] In the United States the FDA recommends not exceeding 3 grams per day of EPA and DHA omega-3 fatty acids, with no more than 2 grams per day from a dietary supplement.

EPA and DHA content

Peroxides can be produced when fish oil spoils. A study commissioned by the government of Norway concluded there would be some health concern related to the regular consumption of oxidized (rancid) fish/marine oils, particularly in regards to the gastrointestinal tract, but there is not enough data to determine the risk. The amount of spoilage and contamination in a supplement depends on the raw materials and processes of extraction, refining, concentration, encapsulation, storage and transportation.[50] reports in its review that it found spoilage in test reports it ordered on some fish oil supplement products.[52]


Dioxins and PCBs may be carcinogenic at low levels of exposure over time. These substances are identified and measured in one of two categories, dioxin-like PCBs and total PCBs. While the U.S. FDA has not set a limit for PCBs in supplements, the Global Organization for EPA and DHA (GOED) has established a guideline allowing for no more than 3 picograms of dioxin-like PCBs per gram of fish oil. In 2012, samples from 35 fish oil supplements were tested for PCBs. Trace amounts of PCBs were found in all samples, and two samples exceeded the GOED‘s limit.[52] Although trace amounts of PCBs contribute to overall PCB exposure, claims the amounts reported by tests it ordered on fish oil supplements are far below those found in a single typical serving of fish.[53]

Dioxins and PCBs

While a serving of fish may contain anywhere from 10 to 1,000 ppb of mercury,[51] fish oil supplements have not been found to contain similar mercury levels.


[50] Fish can accumulate toxins such as mercury, dioxins, and


Fish oil is a commonly used dietary supplement, with sales in the U.S. alone reaching $976 million in 2009.[47] Problems of quality have been identified in periodic tests by independent researchers of marketed supplements containing fish oil and other marine oils. These problems include contamination, inaccurate listing of EPA and DHA levels, spoilage and formulation issues.[48]

Supplement quality and concerns

A 2014 Cochrane review found that, based on two large studies, fish oil supplements did not appear to be effective for maintenance of remission in Crohn's disease.[46]

Crohn's disease

In addition, provision of fish oil during pregnancy may reduce an infant’s sensitization to common food allergens and reduce the prevalence and severity of certain skin diseases in the first year of life. This effect may persist until adolescence with a reduction in prevalence and/or severity of eczema, hay fever and asthma.[45]

Some studies reported better psychomotor development at 30 months of age in infants whose mothers received fish oil supplements for the first four months of lactation.[44] In addition, five-year-old children whose mothers received modest algae based docosahexaenoic acid supplementation for the first 4 months of breastfeeding performed better on a test of sustained attention. This suggests that docosahexaenoic acid intake during early infancy confers long-term benefits on specific aspects of neurodevelopment.[44]


Diets supplemented with cod liver oil have shown beneficial effects on psoriasis.[43]


A Cochrane meta-analysis published in June 2012 found no significant protective effect for cognitive decline for those aged 60 and over and who started taking fatty acids after this age. A co-author of the study said to Time, "Our analysis suggests that there is currently no evidence that omega-3 fatty acid supplements provide a benefit for memory or concentration in later life".[42]

Alzheimer's disease

In a 2011 meta-analysis of PubMed articles about fish oil and depression from 1965 to 2010, researchers found that "nearly all of the treatment efficacy observed in the published literature may be attributable to publication bias."[41]

A 2009 metastudy found that patients taking omega-3 supplements with a higher EPA:DHA ratio experienced less depressive symptoms. The studies provided evidence that EPA may be more efficacious than DHA in treating depression. However, this metastudy concluded that due to the identified limitations of the included studies, larger, randomized trials are needed to confirm these findings.[40]

A 2008 Cochrane systematic review found that limited data is available. In the one eligible study, omega-3s were an effective adjunctive therapy for depressed but not manic symptoms in bipolar disorder. The authors found an "acute need" for more randomised controlled trials.[39]

Mental health

There have been some human trials that have concluded that consuming omega-3 fatty acids slightly reduces blood pressure (DHA could be more effective than EPA). It is important to note that because omega-3 fatty acids can increase the risk of bleeding, a qualified healthcare provider should be consulted before supplementing with fish oil.[38]


A 2008 meta-study by the Canadian Medical Association Journal found fish oil supplementation did not demonstrate any preventative benefit to cardiac patients with ventricular arrhythmias.[36] A 2012 meta-analysis published in the Journal of the American Medical Association, covering 20 studies and 68,680 patients, found that Omega-3 Fatty Acid supplementation did not reduce the chance of death, cardiac death, heart attack or stroke.[37]

There is also some evidence that fish oil may have a beneficial effect on certain abnormal heart rhythms.[33][34] However, a 2012 meta-analysis found no such significant benefit.[35]

The US National Institutes of Health lists three conditions for which fish oil and other omega-3 sources are most highly recommended: hypertriglyceridemia (high triglyceride level), preventing secondary cardiovascular disease, and hypertension (high blood pressure). It then lists 27 other conditions for which there is less evidence. It also lists possible safety concerns: "Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke."[19]

Fish oil supplement studies have failed to support claims of preventing heart attacks or strokes.[3][4][5] Earlier, in 2007, the American Heart Association had recommended the consumption of 1 gram of fish oil daily, preferably by eating fish, for patients with coronary artery disease, but cautioned pregnant and nursing women to avoid eating fish with high potential for mercury contaminants including mackerel, shark, and swordfish.[32] (Optimal dosage was related to body weight.)


The effects of fish oil consumption by humans on prostate cancer is not conclusive.[28][29] There is a decreased risk with higher blood levels of DPA, but an increased risk of more aggressive prostate cancer with higher blood levels of combined EPA and DHA,[30] and some evidence of an association between high blood levels of omega-3 fatty acids and an increased prostate cancer risk.[31]

Prostate cancer

Health effects

In 2005, fish oil production declined in all main producing countries with the exception of Iceland.


Grams of omega-3 fatty acids per 3oz (85g) serving of common non-fish foods.[25]
Name grams
flaxseeds 19.55
chia seeds 14.8
hemp seeds 7.4
walnut 1.7
Soybean 1.1
butter 0.27
Eggs, large regular 0.109[27]
Lean red meat 0.031
Turkey 0.030
Cereals, rice, pasta, etc. 0.00
Fruit 0.00
Milk regular 0.00
Regular bread 0.00
Vegetables 0.00

For comparison, note the omega-3 levels in some common non-fish foods:

Grams of omega-3 fatty acids per 3oz (85g) serving of popular fish.[25][26]
Common name grams
Herring, sardines 1.3–2
Spanish mackerel, Atlantic, Pacific 1.1–1.7
Salmon 1.1–1.9
Halibut 0.60–1.12
Tuna 0.21–1.1
Swordfish 0.97
Greenshell/lipped mussels 0.95[27]
Tilefish 0.9
Tuna (canned, light) 0.17–0.24
Pollock 0.45
Cod 0.15–0.24
Catfish 0.22–0.3
Flounder 0.48
Grouper 0.23
Mahi mahi 0.13
Orange roughy 0.028
Red snapper 0.29
Shark 0.83
King mackerel 0.36
Hoki (blue grenadier) 0.41
Gemfish 0.40
Blue eye cod 0.31
Sydney rock oysters 0.30
Tuna, canned 0.23
Snapper 0.22
Barramundi, saltwater 0.100
Giant tiger prawn 0.100

The most widely available dietary source of EPA and DHA is cold-water oily fish, such as salmon, herring, mackerel, anchovies, and sardines. Oils from these fish have a profile of around seven times as much omega-3 oils as omega-6 oils. Other oily fish, such as tuna, also contain omega-3 in somewhat lesser amounts. Although fish is a dietary source of omega-3 oils, fish do not synthesize them; they obtain them from the algae (microalgae in particular) or plankton in their diets.[24]

Nutritional details

Often marketed and sold for consumption as part of the diet or in dietary supplements in contemporary societies, fish oils also have found roles in external use, as emollients[20] or as general ointments[21] as well as in body art,[22] or for alleged insulation against cold.[23]



  • Uses 1
  • Nutritional details 2
  • Production 3
  • Health effects 4
    • Prostate cancer 4.1
    • Cardiovascular 4.2
    • Hypertension 4.3
    • Mental health 4.4
    • Alzheimer's disease 4.5
    • Psoriasis 4.6
    • Pregnancy 4.7
    • Crohn's disease 4.8
  • Supplement quality and concerns 5
    • Contamination 5.1
    • Mercury 5.2
    • Dioxins and PCBs 5.3
    • Spoilage 5.4
    • EPA and DHA content 5.5
    • Formulation 5.6
    • Prescription fish oil 5.7
  • Dangers 6
    • Maximum intake 6.1
    • Vitamins 6.2
    • Toxic pollutants 6.3
  • See also 7
  • Notes 8
  • References 9
  • External links 10

The omega-3 fatty acids in fish oil are thought to be beneficial in treating hypertriglyceridemia, although claims of preventing heart attacks or strokes have not been supported.[3][4][5] Fish oil and omega-3 fatty acids have been studied in a wide variety of other conditions, such as clinical depression,[14][15] anxiety,[16][17][18] cancer, and macular degeneration, yet benefits in these conditions have not been verified.[19]

[13] Only fatty fish intake, particularly salmonid, and estimated EPA + DHA intake from fatty fish has been observed to be significantly associated with increase in serum EPA + DHA.[13] Studies have revealed that there is no relation between total fish intake or estimated omega−3 fatty acid intake from all fish, and serum omega−3 fatty acid concentrations.[11]