Fish oil
[1][2] 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.
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.
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[9] or as general ointments[10] as well as in body art,[11] or for alleged insulation against cold temperatures.
[13] The most widely available dietary source of EPA and DHA is cold-water oily fish, such as salmon, herring, mackerel, anchovies, and sardines.
For comparison, note the omega−3 levels in some common non-fish foods: Fish oil became one of the earliest dietary supplements, and by the end of the 19th century, was used as a treatment for many diseases, including such ailments as tuberculosis and hysteria.
[25] 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.
[30] However, this evidence from the Select Trial has been challenged on the grounds of methodology and that the quantitative difference between those who developed prostate cancer and those who did not "is so small as to be biologically irrelevant".
[31] There is uncertainty about the role of fish oil in cardiovascular disease, with reviews reaching different conclusions about its potential impact.
[39] A 2008 meta-study found fish oil supplementation did not demonstrate any preventative benefit to cardiac patients with ventricular arrhythmias.
[42] 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).
[44] A 2009 metastudy found that patients taking omega−3 supplements with a higher EPA:DHA ratio experienced fewer depressive symptoms.
However, this metastudy concluded that due to the identified limitations of the included studies, larger, randomized trials are needed to confirm these findings.
[45] 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 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".
[51] 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.
[52] 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.
[59] A report by the Harvard Medical School studied five popular brands of fish oil, including Nordic Ultimate, Kirkland and CVS.
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.
Prescription fish oil products having DHA work by raising LDL-C levels to reduce triglycerides, like fibrates.
[91] 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, such as slower blood clotting.
[95] 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 polychlorinated biphenyl (PCB) levels that exceeded the European Union maximum limits in several fish oil brands,[96][97] which required temporary withdrawal of these brands.
[98] A March 2010 lawsuit filed by a California environmental group claimed that eight 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.
[99][100] 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.
