The role played by the n-3 (omega 3) fatty acids in the development cardiovascular disease is interesting because while the effects of the parent compound α-linolenic acid (ALA, C18:3 (n-3)) are inconsistent, intakes of its metabolites eicosapentanoic acid (EPA, C20:4 (n-3)) and docosahexanoic acid (DHA, C22:6 n-3)) show significant health benefits. Intakes of EPA and DHA, present in high concentrations in fish oil, are inversely related to cardiovascular disease. Both EPA and DHA are likely beneficial because they favourably affect the formation of cellular hormones that regulate inflammation and platelet aggregation. Supplementation of fish oils improves lipoprotein profiles, and in particular lowers levels of fasting triglycerides in the form of the very low density lipoproteins (VLDL). However, fish oils do not appear to lower plasma levels of low density lipoprotein (LDL), which is interesting, because it argues against the requirement to lower LDL in order to prevent cardiovascular disease.
The association between fish oil consumption and cardiovascular disease has been extensively studied in different sub-groups of populations, and generally the results are consistent. For example, one group of researchers1 analysed the lipoprotein subfraction profile of 1214 Alaskan Eskimos using blood samples, and related them to dietary intakes of n-3 long-chain polyunsaturated fatty acids including EPA and DHA. After adjustments for confounding variables, intakes of the n-3 fatty acids were significantly inversely associated with the large VLDL subfraction that represents the newly synthesised hepatic triglycerides. However, while this association was significant in women, the relationship did not reach significance for men. High intakes of n-3 fatty acids were also significantly associated with a smaller VLDL size, an increase in the number of large high density lipoproteins (HDL) and an increase in HDL size (increased HDL2), all regarded as beneficial changes.
These results suggest that n-3 fatty acids are associated with favourable changes to the lipoprotein profiles of Alaskan Eskimos. Interestingly, high intakes of n-3 fatty acids did not affect total LDL concentrations, but they were associated with an increase in the number of the large less dense LDL particles in both sexes, and an increase in the size of LDL particles in women. Because n-3 fatty acids are associated with a reduced risk of cardiovascular disease, but are not associated with a reduction in total LDL concentrations, it is logical to suggest that reductions in total LDL are not necessary in order to reduce the risk of cardiovascular disease. Interestingly, the lipoprotein changes associated with high intakes of n-3 fatty acid intakes are very similar to those seen with the consumption of alcohol. This may reflect the fact that alcohol consumption is associated with increase plasma levels of n-3 fatty acids2.
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