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 and improve hypertriglyceridemia. There has been a great deal of controversy in recent years about the role of fish oil in cardiovascular disease, with recent meta-analyses reaching different conclusions about its potential impact. The most promising evidence supports supplementation for prevention of cardiac death.
Fish oil and omega-3 fatty acids have also been studied in a wide variety of other conditions such as clinical depression, anxiety, cancer, and macular degeneration, yet their benefit in these conditions has also not been verified.
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 the toxic contaminant mercury. Dioxin, PCBs and chlordane are also present. 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.
Marine and freshwater fish oil vary in contents of arachidonic acid, EPA and DHA. The various species range from lean to fatty and their oil content in the tissues has been shown to vary from 0.7% to 15.5%. They also differ in their effects on organ lipids. 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. 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.
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 or as general ointments as well as in body art, or for alleged insulation against cold.
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.
|Spanish mackerel, Atlantic, Pacific||1.1–1.7|
|Tuna (canned, light)||0.17–0.24|
|Hoki (blue grenadier)||0.41|
|Blue eye cod||0.31|
|Sydney rock oyster||0.30|
|Giant tiger prawn||0.100|
For comparison, note the omega-3 levels in some common non-fish foods:
|Eggs, large regular||0.109|
|Lean red meat||0.031|
|Cereals, rice, pasta, etc.||0.00|
In a 2009 letter on a pending revision to the Dietary Guidelines for Americans, the American Heart Association recommended 250–500 mg/day of EPA and DHA. The Guidelines were revised again for 2015-2020; included is a recommendation that adults consume at least eight ounces of a variety of types of fish per week, equating to at least 250 mg/day of EPA + DHA. The Food and Drug Administration recommends not exceeding 3 grams per day of EPA + DHA from all sources, with no more than 2 grams per day from dietary supplements.
The effect of fish oil consumption on prostate cancer is controversial, as one study showed decreased risk with higher blood levels of DPA, whereas another reported increased risk of more aggressive prostate cancer with higher blood levels of combined EPA and DHA. Some evidence indicated an association between high blood levels of omega-3 fatty acids and an increased prostate cancer risk.
There has been a great deal of controversy in recent years about the role of fish oil in cardiovascular disease, with recent meta-analyses reaching different conclusions about its potential impact. Multiple evaluations suggest fish oil has little or no reduction in cardiovascular mortality, in distinction to earlier observational data, though there appears to be a small reduction in the incidence of actual cardiac events and strokes with its use. 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. (Optimal dosage was related to body weight.)
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."
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. 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.
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.
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.
A 2009 metastudy found that patients taking omega-3 supplements with a higher EPA:DHA ratio experienced fewer 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.
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."
A 2014 meta-analysis of eleven trials conducted respectively on patients with a DSM-defined diagnosis of major depressive disorder (MDD) and of eight trials with patients with depressive symptomatology but no diagnosis of MDD demonstrated significant clinical benefit of omega-3 PUFA treatment compared to placebo. The study concluded that: "The use of omega-3 PUFA is effective in patients with diagnosis of MDD and on depressive patients without diagnosis of MDD."
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".
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. 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.
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.
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.
Supplement quality and concerns
Fish oil is a commonly used dietary supplement, with sales in the U.S. alone reaching $976 million in 2009. 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.
Fish can accumulate toxins such as mercury, dioxins, and polychlorinated biphenyls (PCBs), and spoiled fish oil may produce peroxides. There appears to be little risk of contamination by microorganisms, proteins, lysophospholipids, cholesterol, and trans-fats.
Dioxins and PCBs
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. Although trace amounts of PCBs contribute to overall PCB exposure, Consumerlab.com claims the amounts reported by tests it ordered on fish oil supplements are far below those found in a single typical serving of fish.
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. ConsumerLab.com reports in its review that it found spoilage in test reports it ordered on some fish oil supplement products.
EPA and DHA content
According to ConsumerLab.com tests, the concentrations of EPA and DHA in supplements can vary from between 8 and 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. 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. A ConsumerLab.com publication in 2010 claims 3 of 24 fish oil supplements it covered contained less EPA and/or DHA than was claimed on the label. However, the bioavailability of EPA and DHA from both capsular and emulsified fish oils has been shown to be high.
Fish oil supplements are available as liquids or capsules. Some capsules are enteric-coated to pass through the stomach before dissolving in the small intestine, thus helping prevent indigestion and "fish burps". Poorly manufactured enteric-coated products have the potential to release ingredients too early. ConsumerLab.com, a for-profit supplement testing company, reported that 1 of the 24 enteric-coated fish oil supplements it evaluated released ingredients prematurely.
Prescription fish oil
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. The prescription fish oil drugs are not similar to over-the-counter fish oil supplements. They are not be confused with each other. Prescription fish oil is considered a safe and effective option to reduce triglycerides. There are various prescription fish oil products that have been approved and permitted by FDA for increasing triglyceride levels. Prescription fish oil products having DHA raise up the LDL-C levels to reduce triglycerides, like fibrates. Even the heart experts advise that prescription fish oil helps in decreasing additional levels of blood fats. As per the latest guideline, prescription fish oils might only help when triglycerides reaches a specific upper level. Prescription fish oil pills, capsules and tablets have more omega-3 fatty acids than those which are non-prescribed. FDA regularly monitor those drugs for standards, quality and safety.
The FDA recommends that consumers do not exceed more than three grams per day of EPA and DHA combined, with no more than 2 grams from a dietary supplement. 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. 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. A 1987 study found that healthy Greenlandic Inuit had an average intake of 5.7 grams of omega-3 EPA per day which had many effects including prolonged bleeding times, i.e., slower blood clotting.
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).
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.
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, 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.
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 CVS/pharmacy, Nature Made, Rite Aid, GNC, Solgar, Twinlab, Now Health, Omega Protein and Pharmavite. The majority of these products were either cod liver or shark liver oils. Those participating in the lawsuit claim that because the liver is the major filtering and detoxifying organ, PCB content may be higher in liver-based oils than in fish oil produced from the processing of whole fish.
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."
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".
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This becomes abundantly clear in the work of Chinese body artist Zhang Huan. In the course of his career, Zhang Huan has subjected himself to painful trials: sitting motionless for hours in an outhouse covered in honey and fish oil while flies crawled over his body [...].
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Hoffentlich zogen die Eltern in eine Gegend, wo es recht viele Eingeborene gab. Indianer, die nur von Jagd und Fischfang leben. Ach, und womöglich Eskimos, die sich mit Tran einschmieren, um sich gegen die Kälte zu schützen und rohes Fleisch essen [...]. [She hoped her parents would move to an area where there were many aboriginals. Indians who live solely by hunting and fishing. Oh, and if possible Eskimos who smear themselves with fish oil to protect themselves from the cold, and who eat raw meat.]
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- International Fish Oil Standards — An organization concerned with the quality of omega-3 products as it relates to the international standards established by the World Health Organization and the Council For Responsible Nutrition for purity and concentration.
- Joyce A. Nettleton, ed. "PUFA Newsletter". Retrieved 20 February 2006.CS1 maint: extra text: authors list (link) 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.