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 the 21st century about the role of fish oil in cardiovascular disease, with recent meta-analyses reaching different conclusions about its potential impact.
The fish used as sources do not actually produce omega−3 fatty acids. Instead, the fish accumulate the acids by consuming either microalgae or prey fish that have accumulated omega−3 fatty acids. 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. Dioxins, like PCBs and chlordane, as well as other chlorinated cyclodiene insecticides are also present. Fish oil is used in aquaculture feed, in particular for feeding 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 14.5%. They also differ in their effects on organ lipids. Studies have revealed that there is no relation between either 1) total fish intake or 2) 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.
The United States Food and Drug Administration (FDA) has approved four fish oil-based prescription drugs for the management of hypertriglyceridemia, namely Lovaza, Omtryg (both omega-3-acid ethyl esters), Vascepa (ethyl eicosapentaenoic acid), and Epanova (omega-3-carboxylic acids). None of these drugs are actually fish oil; they are all derivatives of acids found in fish oil.
Uses 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 temperatures.Ilse Schreiber: Die Schwestern aus Memel (1936), quoted, and extract translated in:
Fishmeal and fish oil are the principal sources of omega-3 long-chain polyunsaturated fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) in animal feed.
Food sources 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 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.
EPA and DHA are available as dietary supplements most commonly as fish oil capsules, softgels, and gummies,1 krill oil, and less commonly as algae oil.2 Generally, salmon oil has more DHA than EPA while other fish oils such as herring, mackerel, anchovies, sardines, and pollock have more EPA than DHA. (See Supplements section below.)
+Grams of omega−3 fatty acids per serving of popular fish. 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 Tilefish 0.90 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 Silver gemfish 0.40 Blue eye cod 0.31 Sydney rock oyster 0.30 Tuna, canned 0.23 Snapper 0.22 Barramundi, saltwater 0.100 Giant tiger prawn 0.100
For comparison, note the omega−3 levels in some common non-fish foods:
+Grams of omega−3 fatty acids per serving of common non-fish foods. 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 Lean red meat 0.031 Turkey (bird) 0.030 Cereals, rice, pasta, etc. 0.00 Fruit 0.00 Milk, regular 0.00 Bread, regular 0.00 Vegetables 0.00
Research
History
Fish oil became one of the earliest dietary supplements during 1870s, and by the end of the 19th century, was used as a treatment for many diseases, including such ailments as tuberculosis and hysteria. The possible effects of fish oil and omega−3 fatty acids have since been studied in clinical depression, anxiety, cancer, and macular degeneration, yet they have not been proven effective.
Crude fish oil as it is originally sold (especially cod liver oil) contains vitamin A and vitamin D, which was useful in preventing vitamin A deficiency and vitamin D deficiency (the latter manifesting as rickets in urban children). Modern fish oil supplements purified for omega-3 do not claim to contain these two vitamins.
Various recommendations 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 seafood per week, which provide an average of 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.
Prostate cancer There is no good evidence that fish oil supplementation is of benefit for prostate cancer, and omega-3 fatty acids may increase the cancer risk.
Cardiovascular There is uncertainty about the role of fish oil in cardiovascular disease, with reviews reaching different conclusions about its potential impact. Multiple evaluations suggest fish oil has little or no reduction in cardiovascular mortality, although there may be a small reduction in the incidence of actual cardiac events and strokes with its use. In 2007, the American Heart Association 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 or omega-3 fatty acids may increase the risk of hemorrhagic (bleeding) stroke."
There were studies to determine if fish oil had an effect on certain abnormal heart rhythms, although a 2012 meta-analysis found no significant effect.
A 2008 meta-study found fish oil supplementation did not demonstrate any preventative benefit to cardiac patients with ventricular arrhythmias. A 2012 meta-analysis 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. A 2018 meta-analysis of 77,000 participants found a 3% reduction in the relative risk for those who supplemented fish oil; however, this effect was deemed insignificant.
Mental health A 2008 Cochrane systematic review found that limited data is available. In the one eligible study, omega−3s were an effective adjunctive therapy for depressive 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."
Antidepressant A 2019 meta-analysis concluded that EPA ≥ 60% at a dosage of ≤1 g/d may have antidepressant effect.
Alzheimer's disease 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".
Psoriasis Diets supplemented with cod liver oil have shown beneficial effects on psoriasis.
Pregnancy 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.
Crohn's disease 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.
Supplements
Fish oil is a commonly used dietary supplement, with sales in the US reaching $976 million in 2009. By 2020 the global omega−3 supplement market size had reached $5.58 billion, and fish oil based supplements accounted for 63.1% of that market.
Formulation