Regular fish consumption may be beneficial to the health because of the high concentrations of long chain fatty acids, particularly docosahexanoic acid (DHA, C22:6 (n-3)) and eicosapentanoic acid (EPA, C20:5 (n-3)). Research suggests that fish consumption is protective of cardiovascular disease, although the exact mechanism of action is not fully understood. However, research has centred mainly on the ability of the marine long chain fatty acids to influence eicosanoid formation and thus regulate inflammation in tissues. Epidemiological studies consistently show benefits to long term fish consumption, but the reliability of such study methods are often dependent on the accuracy of dietary recall, which can weaken the strength of such research. Studies that measure the fatty acid composition of plasma phospholipids or erythrocytes remove the need to assess the diets of the subjects, and can therefore increase reliability.
For example, one study investigated the association between various fatty acid profiles in erythrocytes and the risk of hypertension in 516 hypertensive subjects pair matched to 516 non-hypertensive controls. Erythrocyte saturated fatty acid content was positively associated with high blood pressure, whereas the cis total polyunsaturated fatty acid, cis n-3 polyunsaturated fatty acid, and the polyunsaturated fatty acid to saturated fatty acid ratio, all showed inverse associations with high blood pressure. The relative risk for hypertension across increasing quartiles for saturated fatty acids were 1.00, 1.19, 1.44 and 1.76, for cis polyunsaturated fatty acids were 1.00, 0.84, 0.88 and 0.56, for n-3 polyunsaturated fatty acids were 1.00, 0.87, 0.66 and 0.65, and for the polyunsaturated to saturated fatty acid ratio were 1.00, 0.99, 0.70 and 0.51. Interestingly, trans and monounsaturated fatty acids in erythrocytes were not associated with hypertension.
Endothelial dysfunction and systemic inflammation are considered risk factors for cardiovascular disease, and increasing numbers of observational studies are reporting associations between diet and the presence of biochemical markers of inflammation and vascular abnormalities. For example, researchers2 have assessed the diets of 301 women and then measured various plasma biomarkers of endothelial dysfunction (soluble intracellular adhesion molecule 1 [slCAM-1], soluble endothelial selectin, soluble vascular cell adhesion molecule 1, soluble thrombomodulin), and systemic inflammation (C-reactive protein, serum amyloid A, interleukin 6, interleukin 8, tumour necrosis factor α and slCAM-1). Of the foods investigated, consumption of fish (per 100g/wk), but no other food group, was inversely associated with changes in endothelial dysfunction and systemic inflammation. Both EPA and DHA intake was inversely associated with changes to endothelial dysfunction and systemic inflammation, and explained 83 and 40% of the association.
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