Influence of variation in fat composition on haemostatic variables.

The effects of saturated fatty acids on platelet function remain uncertain although hypercholesterolaemia is associated with increased platelet aggregrability. The consumption of n-3 fatty acids as fish oils leads to a reduction in the concentration of arachidonic acid (20:4n-6) in platelets and endothelial cells and its replacement with eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA). This change is accompanied by a prolongation of template bleeding time. The effect of replacing arachidonic acid with EPA and DHA is to decrease the production of thromboxane A2 and increase that of the antiaggregatory prostacyclins. Despite the association between plasma triglyceride concentrations and impaired fibrinolytic activity, there is little evidence to suggest that the type of fat influences PAI-1, tPA or global markers of fibrinolysis. Some studies have reported that plasma fibrinogen concentration may be decreased by n-3 fatty acids but a large number have found no effect. Plasma triglyceride concentrations are strongly associated with increased factor VII coagulant activity (FVIIc). Despite their well known hypotriglyceridaemic effects, n-3 fatty acids do not decrease FVIIc. Postprandial activation of FVII is now well recognised and oleic acid appears to be among the most potent activators. These effects are, however, dose related. In view of their potentially prothrombotic influence, it would be wise to caution against high intakes of fat in the middle-aged and elderly population who are most at risk.