The omega-3 fatty acids — alpha-linolenic acid (ALA, 18:3 n-3), eicosapentaenoic acid (EPA, 20:5 n-3), and docosahexaenoic acid (DHA, 22:6 n-3) — are the polyunsaturated fatty acids that are the foundation of all anti-inflammatory lipid mediators and that are the essential structural components of the cell membranes of the brain, the retina, and the cardiac muscle. ALA is the essential omega-3 fatty acid — it cannot be synthesised by the human body and must be obtained from the diet; EPA and DHA can be synthesised from ALA, but the conversion rate is low (approximately 5-10% for EPA and 1-3% for DHA), making direct dietary EPA and DHA intake essential for the maintenance of optimal EPA and DHA status. The omega-3 fatty acids are found in fatty fish (salmon, mackerel, sardines, anchovies, herring), in fish oils, in the algae from which fish accumulate EPA and DHA, and in the seeds and nuts of certain plants (flaxseed, chia seeds, hemp seeds, walnuts). The Western diet is typically very low in omega-3 fatty acids (with an omega-6 to omega-3 ratio of approximately 15-20:1, compared to the 4:1 ratio that is considered optimal), and this omega-3 deficiency is one of the most important dietary contributors to the chronic inflammation that is the pathological basis of cardiovascular disease, metabolic syndrome, type 2 diabetes, obesity, neurodegenerative disease, and the inflammatory skin conditions that are endemic to the modern Western diet.
Eicosanoids and the Inflammatory Response
The eicosanoids are the lipid signalling molecules that are synthesised from the omega-6 fatty acid arachidonic acid (AA, 20:4 n-6) and from the omega-3 fatty acid EPA, and they are the primary mediators of the inflammatory response. The AA-derived eicosanoids — including the prostaglandins (particularly PGE2), the thromboxanes (particularly TXA2), and the leukotrienes (particularly LTB4) — are potently pro-inflammatory — they increase vasodilation and vascular permeability (producing the redness and swelling of acute inflammation), they attract neutrophils and other immune cells to the site of inflammation (chemotaxis), they promote the formation of the fibrin clots that wall off the site of infection, and they mediate the pain and fever that are the classic symptoms of inflammation. The EPA-derived eicosanoids — including the prostaglandins of the 3-series (PGE3) and the leukotrienes of the 5-series (LTB5) — are much less pro-inflammatory than the AA-derived eicosanoids, and they actively promote the resolution of inflammation by stimulating the synthesis of the specialised pro-resolving mediators (SPMs) — including the resolvins, the protectins, and the maresins — that are the lipid mediators that actively resolve inflammation and promote tissue repair.
The clinical importance of the omega-3 to omega-6 ratio is underscored by the observation that the chronic inflammation that is characteristic of the Western diet — and that underlies the cardiovascular disease, the metabolic syndrome, the type 2 diabetes, and the inflammatory skin conditions that are endemic to Western civilisation — is driven in large part by the high omega-6 and low omega-3 fatty acid intake that is typical of the modern diet. When the omega-6 to omega-3 ratio is elevated (as in the Western diet), the AA-derived eicosanoids predominate, the SPMs are not synthesised in adequate amounts, the acute inflammatory response is not resolved, and the chronic, low-grade inflammation that is the pathological basis of the chronic diseases of civilisation develops. The reduction of the omega-6 to omega-3 ratio through increased omega-3 intake (through fatty fish, fish oils, or algae oils) is one of the most important dietary interventions for the prevention and the treatment of chronic inflammatory disease.
Omega-3 Fatty Acids and Cardiovascular Health
The cardiovascular benefits of omega-3 fatty acids are among the most well-documented in nutritional science — multiple large RCTs and meta-analyses have demonstrated that omega-3 supplementation (at 1-4g daily of combined EPA and DHA) reduces the risk of cardiovascular events (including myocardial infarction, stroke, and cardiovascular death) in both primary prevention (people without known cardiovascular disease) and in secondary prevention (people with established cardiovascular disease). The GISSI-Prevenzione trial (in 11,324 patients with recent myocardial infarction) found that omega-3 supplementation at 1g daily reduced all-cause mortality by approximately 20% and cardiovascular mortality by approximately 30% over 3.5 years of follow-up. The mechanism of this cardiovascular benefit involves multiple effects — the anti-inflammatory effects (through the reduction of the omega-6 to omega-3 ratio and the promotion of inflammation resolution), the triglyceride-lowering effects (through the reduction of VLDL synthesis and the enhancement of VLDL clearance), the anti-platelet effects (through the reduction of TXA2 production), and the blood pressure-lowering effects (through the vasodilatory effects of the EPA-derived eicosanoids).
Practical Application
For general omega-3 supplementation, the evidence-based dose is 1-4g of combined EPA and DHA daily (from fish oils or algae oils, the preferred source for vegetarians and vegans), taken with a fat-containing meal for optimal absorption. The recommended intake of omega-3 fatty acids is approximately 250-500mg of combined EPA and DHA daily for general cardiovascular health, 2-4g daily for the reduction of elevated triglycerides, and 3-4g daily for the anti-inflammatory effects that are therapeutic in inflammatory conditions. For comprehensive anti-inflammatory support, omega-3 fatty acids pair well with the Mediterranean dietary pattern (which is naturally low in omega-6 fatty acids and high in omega-3 fatty acids, olive oil, fruits, vegetables, and fish), with the turmeric and curcumin preparations (which have additional anti-inflammatory effects through the inhibition of the NF-kappaB and COX-2 pathways), with vitamin D (which has complementary anti-inflammatory and immunomodulatory effects), and with the magnesium (which has anti-inflammatory effects and which is often deficient in people with chronic inflammatory conditions).
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