The consumption of fish can make significant contributions, at different levels, for specific health issues, some of which are described below.

Thrombosis

A heart attack can result when an artery, which has already been narrowed by fatty deposits (atherosclerosis), becomes completely blocked.

This is caused by blood platelets sticking together and forming a clot (thrombus). Platelet aggregation is triggered when the endothelial cells that line the arter walls are damaged in some way. Both the endothelial cells and the platelets produce eicosanoids , which cause the platelets to clump together.

When the diet is rich in fish oil it is thought that different eicosanoids are produced and that these prevent the formation of a clot.

OTHER POSSIBILITIES

An increase in fish oils in the diet results in a marked reduction in blood triglyceride levels. The exact significance of an elevated triglyceride level remains controversial.

One recent Norwegian study has shown that women with high triglyceride levels have up to 5 times the risk of a heart attack compared to women with normal levels. The impact of high triglyceride levels was found to be independent of other risk factors.

Fish oils have no effect on the levels of low density lipoprotein cholesterol (LDL) but they do raise high density lipoprotein (HDL). HDL is a protective type of lipoprotein since it takes excess cholesterol away from the tissues and returns it to the liver. Fish oils normally raise HDL levels by about 10%, however intakes of over 10 g per day may actually decrease HDL levels.

Diseased heart muscle is susceptible to bouts of irregular electrical activity (arrhythmias), which are potentially lethal and often cause sudden cardiac death. There is some evidence from animal studies and very limited evidence from clinical studies that increasing fish oil in the diet helps to reduce these cardiac arrhythmias.

Raised blood pressure is know to be a major risk factor in CHD. Most studies on the effects of fish oil gicen as dietary supplements (supplying 3 g or more per day of n-3 PUFA) have shown modest reductions in blood pressure, especially in people with raised blood pressure. This however is the equivalent of 10 portions of oil-rich fish each week and would be difficult to achieve from diet alone. Combining an increase in fish intake with a low sodium diet might be a more effective means of reducing blood pressure.

based on the documentation of "Nutritional Aspects of Fish" prepared by the Irish Sea Fisheries Board (AN BORD IASCAIGH MHARA)