Eicosapentaenoic acid (EPA) is a long-chain omega-3 polyunsaturated fatty acid derived from the tissues of oily fish and marine mammals. It is found in greatest concentration in the livers of fish; otherwise it is widely available as a nutritional supplement. Eicosapentaenoic Acid inhibits two of the most inflammatory pathways in the body, cyclooxygenase and lipoxygenase, by competing with arachidonic acid in these complicated processes. 
These pathways are the targets of several types of anti-inflammatory prescription medications, including aspirin and the more recently developed Cox-inhibitors. In humans, Eicosapentaenoic Acid can be derived from another fatty acid that is similar in chemical structure, docosahexaenoic acid (DHA).  The term ‘essential fatty acid’ relates to the fact that these are a grouping of fats necessary for human health. Like ‘essential’ amino acids, these fats must too be obtained from outside the body; either by dietary sources, supplementation, or a combination of both.
Eicosapentaenoic Acid should not be confused with DHA. While most commercial fish oil products contain varying amounts of both oils, they each have Eicosapentaenoic Acid rate effects. Much of the research surrounding Eicosapentaenoic Acid was performed using fish oil products containing both omega-3 polyunsaturated fatty acids, rather than solitary dosing of only EPA.
Although widely available in purified form as a supplement, EPA is found in nearly all forms of seafood, most notably cold water fish. Popular cold water fishes include; salmon, herring, sardines, halibut, bluefish, tuna, and mackerel. In fact, the colder the environment from which the fish is found, the higher its content of EPA. This is important to keep in mind as farm raised fish (including those listed above) are typically very low in EPA and other omega-3 fatty acids. They are not feed algae, nor do they live in an extremely cold environments like wild fish. Sea algae provides some of the precursor material for fatty acid development in fish.
Eicosapentaenoic Acid, included with docosahexaenoic acid (DHA), comprise what are known as essential fatty acids (EFAs). The anti inflammatory effects of Eicosapentaenoic Acid lend to its wide use in inflammatory conditions in the body. By altering the balance between arachidonic acid and its metabolites, supplementation with Eicosapentaenoic Acid has been shown to benefit those with psoriasis lesions. 
Eicosapentaenoic Acid has also been used in depression; it was shown to decrease symptoms of depressed mood, worthlessness, feelings of guilt, and insomnia after two weeks of therapy.  Similarly, Eicosapentaenoic Acid has benefits in moderately, to severe borderline personality disorder as well. Subjects who took Eicosapentaenoic Acid for a period of two months showed moderate improvement in symptoms of aggressive behavior and depression.  Of note, this particular study focused on female subjects and the dose was only one gram of the oil per day.
Other conditions of the mind that are remedied with Eicosapentaenoic Acid supplementation included schizophrenia; subject’s symptoms were significantly reduced after a 12-week Eicosapentaenoic Acid supplementation period. 
Eicosapentaenoic Acid may be of equal importance regarding altering immune system function. Preliminary research shows that Eicosapentaenoic Acid, when taken in moderate amounts, can significantly decrease the amount of natural killer (NK) cell activity.  Investigators believe that this effect may be beneficial in cases involving bone marrow and organ transplant; thereby decreasing the chances of rejection by the organ recipient. The decrease in NK cell activity was noted to be fully reversible four weeks after discontinuing supplementation in the aforementioned study.
Eicosapentaenoic Acid can also benefit certain aspects of blood lipids, or fats within the blood. Eicosapentaenoic Acid alone appears to lower the concentration of triglycerides in the blood stream, but does not seem to affect low-density lipoprotein (LDL) cholesterol levels in those choosing to supplementing with it.  Additionally, Eicosapentaenoic Acid was noted to increase the level of high-density lipoprotein (HDL) cholesterol in subjects by nearly 12% after only six weeks of supplementation, despite having no changes applied to the test subjects regular diets. 
Other effects that Eicosapentaenoic Acid has on the blood stream include;
- altering blood viscosity, or thickness of the blood
- allows for greater red blood cell deformability
- decreasing platelet aggregation, or stickiness
This means that red blood cells can fit through smaller blood vessels throughout the body, decreasing the chance of tissue damage from lack of blood supply. Platelets, whose primary job is to create blood clots, are also less inclined to create unneeded clots in the body.  Eicosapentaenoic Acid does not appear to influence other clotting factors (i.e. fibrinogen level, plasminogen activator-inhibitor, or tissue plasminogen activator activity) in the blood, making it a safe supplement for increasing peripheral vascular health. 
There is no established RDA for Eicosapentaenoic Acid. Eicosapentaenoic acid (Eicosapentaenoic Acid) is typically combined with DHA (docosahexaenoic acid) in prEicosapentaenoic Acidrations that are labeled as fish oil. The same is true when consuming fish itself; both oils are mixed in different concentrations in seafood.
Studies investigating the health effects of Eicosapentaenoic Acid (mentioned above) used Eicosapentaenoic Acid in amounts ranging from one to three grams per day. Typically, fish oil prEicosapentaenoic Acid rations contain Eicosapentaenoic Acid and DHA in, roughly, a 2:1 or 3:1 ratio.
Diets that contain no cold-water marine animal sources may be low in Eicosapentaenoic Acid. Likewise, diets low in animal foods, seeds, or nuts, may also be further depleting. This being said, the majority of Americans (and most of the modern world that consumes primarily processed foods) are thought to be low and or deficient in essential fatty acids in general; of which Eicosapentaenoic Acid is a major component.
In fact, one popular theory exists which proclaims that humans evolved on a diet consisting of a 1:1 ratio of omega-6 to omega-3 fatty acids. Today, however, the typical Processed/Western diet consists of a ratio between 10:1 and 25:1, and in some cases may be as high as 40:1. (that is, processed : western foods) It is this imbalanced fatty acid ratio that is thought to be a major contributor to chronic inflammatory health problems. 
A common misconception is that all commonly consumed omega-6 fatty acids (i.e Linoleic Acid, Arachidonic Acid, and Gamma Linolenic Acid) are unhealthful, when the reality is that only excessive intake of omega-6 fatty acids (combined with decreased omega-3 fatty acids) contribute to chronic inflammation. Both of these fatty acids are necessary in performing many essential functions within the body.
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