he fish oils eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)) are increasingly being seen as beneficial to the health. In particular high intakes of fish oil have been shown to favourably modulate plasma triglycerides, possibly because they increase β-oxidation of fatty acids. High intakes of both EPA and DHA are also known to modulate the eicosanoid pathways which includes the production of prostaglandins, leukotrienes and thromoxanes. This has a number of favourable effects including reductions in systemic inflammation and platelet aggregation. The triglyceride and eicosanoid modulating effects of fish oils may explain their beneficial effects at reducing the risk of cardiovascular disease. However, assessing intakes of these fish oils relies on the presence of reliable biomarkers, and recent evidence suggests that both acute and chronic intakes can be effectively assessed through analysis of plasma.
Researchers have assessed the best biomarkers for EPA and DHA in human plasma and reported that plasma phosphatidylcholine EPA and DHA are the most suitable biomarker for short-term intake. This is because plasma phosphatidylcholine EPA and DHA rapidly increases with increasing fish oil intake, and also rapidly diminishes as intakes fall. It takes roughly 1 to 2 weeks for dietary increases in EPA and DHA to be reflected in increased phosphatidylcholine concentrations. In contrast, platelet concentrations of EPA and DHA rise more slowly as fish oil intakes increase, and therefore only long-term intakes can cause large rises in platelet concentrations. It takes roughly 3 to 4 weeks for dietary intakes of EPA and DHA to be reflected in increased platelet concentrations of EPA and DHA. Both plasma phosphatidylcholine EPA and DHA and platelet EPA and DHA showed good dose responses.
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