Marine oils, lipids extracted from cold-water fish and from sea mammals, are rich in omega-3 (N-3, ω-3) unsaturated fatty acids. These fatty acids affect (decrease) platelet aggregation because they stimulate the synthesis of thromboxane A3. Thromboxane A3 does not have the platelet-aggregating property of the other eicosanoids. In addition, eicosapentaenoic acid is used to make the antiaggregating prostaglandin PGI3. Animals fed ω3-rich oils produce significantly more of the eicosanoids of the leukotrine B5 (LTB5) series. LTB4 is an important inflammatory mediator whereas LTB5 is not. Fish oil consumption results in an increased neutrophil LTB5 production with a concomitant decrease in LTB4 production. This diet-influenced change in LTB4 and LTB5 production seems to be related to a reduced incidence of autoimmune-inflammatory disorders such as asthma, psoriasis, and rheumatoid arthritis in populations consuming co3 fatty acids routinely. Tumorigenesis likewise can be influenced by the relative amounts of the various eicosanoids. Prostaglandin G of the 2-series acts as a tumor promoter. It downregulates macrophage tumoricidal activities and inhibits interleukin-2 production. Increased PGE2 levels (from ®6 fatty acids) have been associated with aggressive growth patterns of both basal and squamous cell skin carcinomas in humans. Products of the lipooxygenase pathway (stimulated by the 00-3 fatty acids) have the reverse effect.
A dietary supplement used to prevent heart disease. Although controlled trials of its effects have had some inconsistent results, trials of secondary prevention (i.e., trials that measure whether second heart attacks can be reduced in patients with a previous history of myocardial infarction) have generally shown that fish oil is effective. It has been shown not to help prevent sudden death in patients who have implanted cardioverter defibrillators. Fish oil concentrates provide omega-3 and omega-6 fatty acids, which reduce inflammation mediated by arachidonic acid.
A substance found naturally in certain types of oily fish, like mackerel, is used in making fish-oil supplements. These supplements, abundant in omega-3 fatty acids, are utilized as medications to reduce lipid levels.