Omega-3 Fatty Acids
The positive CV effects of the Mediterranean diet may be attributed, in part, to the high omega-3 fatty acid composition in the diet. Epidemiological studies conducted in the 1970s demonstrated that the Inuit Eskimo population in Greenland had significantly lower death rates from CV disease compared with the Danish population, despite similar cholesterol levels. The Inuit dietary pattern is high in fat, predominantly due to intake of omega-3 fatty acids from whale, seal, and fish.
The omega-3 fatty acids are long-chain polyunsaturated fatty acids (18-22 carbon atoms in length) with many double bonds in their chemical structure. The first carbon-carbon double bond is located at the third carbon (omega-3) from the methyl end of the fatty acid. The 18-carbon omega-3 fatty acid, α-linolenic acid (ALA), is classified as "essential" because it cannot be synthesized endogenously and is obtained from the diet. This essential fatty acid and its longer chain derivatives (20-carbon fatty acid, eicosapentaenoic [EPA] and 22-carbon fatty acid, docosahexaenoic [DHA]) are vital for growth and development, and they are important for neurologic and CV processes. Omega-3 fatty acids are typically derived from both plant and marine sources. The plant-derived form, ALA, is found in canola, soybean, flaxseed, and walnut oils as well as dark green leafy vegetables like kale and collard greens. The marine-derived forms, EPA and DHA, are found predominantly in fatty, cold-water fish (mackerel, herring, salmon, trout, sardines, and albacore tuna). EPA and DHA can also be metabolized to a limited extent from ALA. In comparison, rich sources of monounsaturated fats include olive oil, avocados, and nuts.
Multiple lines of evidence show that omega-3 fatty acids have a wide range of physiological effects that are cardioprotective. Investigations have shown that omega-3 fatty acids lower triglycerides and may improve the quality of lipoproteins by shifting the particle distribution to large, buoyant LDL.
Numerous studies have documented the blood pressure-lowering effects of the omega-3 fatty acids in hypertension.[21,22] These effects may be attributed to the vasorelaxant properties of omega-3 fatty acids. This has been demonstrated in experimental models of hypertension, hypercholesterolemia, and aging.[24,25,26] Moreover, a recent clinical trial in hyperlipidemic children demonstrated that daily supplementation with DHA (1.2 g) improves endothelial function. A possible mechanism for this effect is an increase in the production of vasodilatory nitric oxide from the vascular endothelium.[28,29]
Other studies suggest that omega-3 fatty acids prevent atrial and ventricular arrhythmias.[30,31,32] The antiarrhythmic effect of omega-3 fatty acids may account for the significant reduction in sudden cardiac death after myocardial infarction (MI). The omega-3 index, a measure of EPA and DHA composition in red blood cells, has been proposed as an indicator for risk of death from CHD. It has been suggested that an omega-3 index of ≥8% is a target goal for cardioprotection. Intake of approximately 900 mg/d of EPA and DHA is equivalent to an omega-3 index of 9.5%.
Omega-3 fatty acids also have anti-thrombotic and anti-inflammatory properties. Platelet aggregation is inhibited, which reduces thrombus formation and risk for an acute coronary event. Omega-3 fatty acids reportedly diminish the inflammatory response associated with atherogenesis by attenuating the expression of endothelial cell adhesion molecules.[36,37]
The totality of evidence suggests that omega-3 fatty acids, integral components of the Mediterranean diet, are important bioactive nutrients that modulate many important physiological responses in the CV system.
Prog Cardiovasc Nurs. 2005;20(2):70-76. © 2005 Le Jacq Communications, Inc.
© 2007 Prog Cardiovasc Nurs
Cite this: The Mediterranean Diet: Is It Cardioprotective? - Medscape - May 01, 2005.