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A typical fish oil softgel; not to scale

Fish oil is oil derived from the tissues of oily fish. It is recommended[1] for a healthy diet because it contains the omega-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), precursors to eicosanoids that reduce inflammation throughout the body. Fish do not actually produce omega-3 fatty acids, but instead accumulate them from either consuming microalgae that produce these fatty acids, as is the case with fish like herring and sardines, or, as is the case with fatty predatory fish, by eating prey fish that have accumulated omega-3 fatty acids from microalgae. Such fatty predatory fish like mackerel, lake trout, flounder, albacore tuna and salmon may be high in omega-3 fatty acids, but due to their position at the top of the food chain, these species can accumulate toxic substances (see biomagnification). For this reason, the FDA recommends limiting consumption of certain (predatory) fish species (e.g. albacore tuna, shark, and swordfish) due to high levels of toxic contaminants such as mercury, dioxin, PCBs and chlordane.[2] More than 50 percent of the world fish oil production is fed to farmed salmon.[3]

Contents

Toxic pollutants in supplements

Fish oil supplements have sometimes come under scrutiny in recent years. In early 2006, government agencies such as the Food Standards Agency in the UK and the Food Safety Authority of Ireland reported PCB levels that exceeded the strict new European maximum limits in several fish oil brands,[4][5] which required temporary withdrawal of these brands. To address the growing concern over contaminated fish oil supplements, the International Fish Oil Standards program, a voluntary review process, was created at University of Guelph.

Patented production purification processes do however exist in order to remove pollutants and dioxins from fish oil to levels far below the EU limits.

EU regulations have set a limit on the percentage of toxins that can be present in the oil for it to still be beneficial to the consumer. Recently, concerns in the UK and Ireland with regards to upholding the limits set have resulted in some major manufacturers taking their products off the market on a temporary basis.

A March 2010 lawsuit filed by a California environmental group revealed that eight popular brands of fish oil supplements contained excessive levels of PCBs, including CVS/pharmacy, Nature Made, Rite Aid, GNC, Solgar, Twinlab, Now Health, Omega Protein and Pharmavite.[6][7]

Production

In 2005, fish oil production declined in all main producing countries with the exception of Iceland. The 2005 production estimate is about 570,000 tonnes in the five main exporting countries (Peru, Denmark, Chile, Iceland and Norway), a 12% decline from the 650,000 tonnes produced in 2004.

Peru continues to be the main fish oil producer worldwide, with about one fourth of total fish oil production. Though Peruvian catches of fish destined for reduction in 2005 were more or less in line with the 2004 result, fish oil production declined from 350,000 tonnes to 290,000 tonnes, due to lower fat content of the fish. In the recent summer months, the fat content was as low as 2% which compares to 4% in 2004. Despite an 18% decline in production, Peruvian earnings from fish oil exports reached 156 million US$ in 2005, exceeding the 2004 income by 6 million US$. This was due to the impressive increase in fish oil prices.

Benefits

Cancer

Several studies report possible anti-cancer effects of n−3 fatty acids found in fish oil (particularly breast, colon and prostate cancer).[8][9][10] Omega-3 fatty acids reduced prostate cancer growth, slowed histopathological progression, and increased survival.[11] Among n-3 fatty acids (omega-3), neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of docosahexaenoic acid, however, the most abundant n-3 PUFA (omega-3) in erythrocyte membranes, were associated with a reduced risk of breast cancer.[12]

Cardiovascular

Some experts[13] believe that taking fish oil (in any form) can help regulate cholesterol in the body, because fish oil has high levels of omega-3 fatty acids. The regulation occurs through effects of the EPA and DHA constituents on Peroxisome proliferator-activated receptor alpha (PPARα). Besides cholesterol regulation, benefits include anti-inflammatory properties and positive effects on body composition. However, the preferred source of omega-3 should be from the fish's body, not the liver. 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. Early explorers to the Arctic were given raw liver by the Inuit, which contained a toxic overdose of vitamin A for the white explorers; however, the same amount was harmless to the Inuit, who had no other source of Vitamin A except animal livers.[citation needed] Studies[14][15] were conducted on prisoners in England where the inmates were fed seafood which contains omega-3 fatty acids. The higher consumption of these fatty acids corresponded with a drop in the assault rates. Another Finnish study found that prisoners who were convicted of violence had lower levels of omega–3 fatty acids than prisoners convicted of nonviolent offenses. It was suggested that these kinds of fatty acids are responsible for the neuronal growth of the frontal cortex of the brain which, it is further alleged, is the seat of personal behavior.

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.[16]

The American Heart Association recommends the consumption of 1g of fish oil daily, preferably by eating fish, for patients with coronary heart disease.[17] Note that optimal dosage relates 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, secondary cardiovascular disease prevention and 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."[18]

Mental health

Studies published in 2004 and 2009 have suggested that fish oil may reduce the risk of depression, and importantly, suicide risk. One such study[19] took blood samples of 100 suicide-attempt patients and compared the blood samples to those of controls and found that levels of Eicosapentaenoic acid were significantly lower in the washed red blood cells of the suicide-attempt patients. A small American trial, published in 2009, suggests that E-EPA, as monotherapy, might treat major depressive disorder, however the study achieved no statistical significance.[20]

A study from the Orygen Research Centre in Melbourne suggests that omega-3 fatty acids could also help delay or prevent the onset of schizophrenia. The researchers enlisted 81 'high risk' young people aged 13 to 24 who had previously suffered brief hallucinations or delusions and gave half of them capsules of fish oil while the other half received fish-tasting dummy substitute. One year on, only three percent of those on fish oil had developed schizophrenia compared to 28 percent from those on the substitute [21].

Alzheimer's

According to a study from Louisiana State University in September 2005, fish oil may help protect the brain from cognitive problems associated with Alzheimer's disease.[22]

Parkinson's

A study[23] examining whether omega-3 exerts neuroprotective action in Parkinson's disease found that it did, using an experimental model, exhibit a protective effect (much like it did for Alzheimer's disease as well). The scientists exposed mice to either a control or a high omega-3 diet from two to twelve months of age and then treated them with a neurotoxin commonly used as an experimental model for Parkinson's. The scientists found that high doses of omega-3 given to the experimental group completely prevented the neurotoxin-induced decrease of dopamine that ordinarily occurs. Since Parkinson's is a disease caused by disruption of the dopamine system, this protective effect exhibited could show promise for future research in the prevention of Parkinson's disease.

References

  1. ^ Moghadasian MH (May 2008). "Advances in dietary enrichment with n-3 fatty acids". Critical Reviews in Food Science and Nutrition 48 (5): 402–10. doi:10.1080/10408390701424303. PMID 18464030. 
  2. ^ EPA (2007-01-31). "Fish Consumption Advisories". http://www.epa.gov/mercury/advisories.htm. Retrieved 2007-02-08. 
  3. ^ FAO: World Review of Fisheries and Aquaculture 2008: Highlights of Special Studies Rome.
  4. ^ Jess Halliday (2006-04-13). "Dioxins prompt second UK fish oil withdrawal". http://www.foodproductiondaily.com/news/ng.asp?n=67059-boots-seven-seas-dioxins-fish-oil. Retrieved 2007-02-08. 
  5. ^ "Pollutants found in fish oil capsules". BBC News. 2002-04-06. http://news.bbc.co.uk/1/hi/health/1911312.stm. Retrieved 2007-02-08. 
  6. ^ Elisabeth Leamy (2010-03-03). "Lawsuit Raises Fish Oil Supplement Concerns". http://abcnews.go.com/GMA/ConsumerNews/truth-fish-oil-concerns/story?id=9994049. Retrieved 2010-03-05. 
  7. ^ "Lawsuit says fish oil supplements contain PCB", San Francisco Chronicle, March 3, 2010
  8. ^ Augustsson K, Michaud DS, Rimm EB, et al (January 1, 2003). "A prospective study of intake of fish and marine fatty acids and prostate cancer". Cancer Epidemiol. Biomarkers Prev. 12 (1): 64–7. PMID 12540506. http://cebp.aacrjournals.org/cgi/pmidlookup?view=long&pmid=12540506. 
  9. ^ De Deckere, EA (July 1999). "Possible beneficial effect of fish and fish n−3 polyunsaturated fatty acids in breast and colorectal cancer". European Journal of Cancer Prevention 8 (3): 213–21. doi:10.1097/00008469-199906000-00009. PMID 10443950. 
  10. ^ Caygill, C.P.; Hill, MJ (August 1995). "Fish, n−3 fatty acids and human colorectal and breast cancer mortality". European Journal of Cancer Prevention 4 (4): 329–32. doi:10.1097/00008469-199508000-00008. PMID 7549825. 
  11. ^ Berquin IM, Min Y, Wu R, et al (July 2007). "Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids". J Clin Invest. 117 (7): 1866–75. doi:10.1172/JCI31494. PMID 17607361. 
  12. ^ Valeria Pala, Vittorio Krogh, Paola Muti, Véronique Chajès, Elio Riboli, Andrea Micheli, Mitra Saadatian, Sabina Sieri, Franco Berrino (July 18, 2001). "Erythrocyte Membrane Fatty Acids and Subsequent Breast Cancer: a Prospective Italian Study". JNCL 93 (14): 1088. doi:10.1093/jnci/93.14.1088. PMID 11459870. http://jnci.oxfordjournals.org/cgi/content/full/93/14/1088. Retrieved 2008-11-30. 
  13. ^ Dr. Michael Main interview on heart health on Steve Kraske's Up to Date
  14. ^ STEPHEN MIHM (2006-04-16). "Does Eating Salmon Lower the Murder Rate?". NYTimes. http://www.nytimes.com/2006/04/16/magazine/16wwln_idealab.html?ex=1302840000&en=42040a1da92a9fe6&ei=5090&partner=rssuserland&emc=rss. Retrieved 2007-02-08. 
  15. ^ Gesch CB, Hammond SM, Hampson SE, Eves A, Crowder MJ (2002). "Influence of supplementary vitamins, minerals and essential fatty acids on the antisocial behaviour of young adult prisoners. Randomised, placebo-controlled trial". The British Journal of Psychiatry : the journal of mental science 181: 22–8. doi:10.1192/bjp.181.1.22. PMID 12091259. 
  16. ^ Nair GM, Connolly SJ (January 2008). "Should patients with cardiovascular disease take fish oil?". CMAJ 178 (2): 181–2. doi:10.1503/cmaj.071654. PMID 18195293. PMC 2174997. http://www.cmaj.ca/cgi/content/full/178/2/181. 
  17. ^ "Fish and Omega-3 Fatty Acids". American Heart Association. http://www.americanheart.org/presenter.jhtml?identifier=4632. Retrieved 2007-02-09. 
  18. ^ NIH Medline Plus. "MedlinePlus Herbs and Supplements: Omega-3 fatty acids, fish oil, alpha-linolenic acid". http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-fishoil.html. Retrieved 2006-02-14. 
  19. ^ Huan M, Hamazaki K, Sun Y, Itomura M, Liu H, Kang W, Watanabe S, Terasawa K, Hamazaki T. (2004). "Suicide attempt and n-3 fatty acid levels in red blood cells: a case control study in China". Biological psychiatry 56 (7): 490–6. doi:10.1016/j.biopsych.2004.06.028. PMID 1540784. http://www.journals.elsevierhealth.com/periodicals/bps/article/PIIS0006322304007061/abstract. 
  20. ^ Mischoulon D, Papakostas GI, Dording CM, et al. A double-blind, randomized controlled trial of ethyl-eicosapentaenoate for major depressive disorder. J Clin Psychiatry. 2009 Aug 25. Abstract
  21. ^ http://archpsyc.ama-assn.org/cgi/content/abstract/67/2/146
  22. ^ Walter J. Lukiw; Cui, JG; Marcheselli, VL; Bodker, M; Botkjaer, A; Gotlinger, K; Serhan, CN; Bazan, NG (2005-06-28). "A role for docosahexaenoic acid–derived neuroprotectin D1 in neural cell survival and Alzheimer disease". J. Clin. Invest 115 (10): 2774–83. doi:10.1172/JCI25420. PMID 16151530. PMC 1199531. http://www.jci.org/cgi/content/abstract/115/10/2774. 
  23. ^ M. Bousquet, M. Saint-Pierre, C. Julien, N. Salem Jr., F. Cicchetti, and F. Calon (2007). "Beneficial effects of dietary omega-3 polyunsaturated fatty acid on toxin-induced neuronal degeneration in an animal model of Parkinson’s disease". The Federation of American Societies for Experimental Biology 22 (4): 1213. doi:10.1096/fj.07-9677com. PMID 18032633. http://www.fasebj.org/cgi/content/abstract/fj.07-9677comv1. 

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