Fish oils have been shown to offer protection against the development of cardiovascular disease. Fish oils are effective at lowering plasma triglycerides, and this may relate to the ability of the long chain marine oils to stimulate the oxidation of fatty acids within the liver, as well as increase insulin sensitivity. The cardioprotective effects of fish oils eicosapentaenoic acid (EPA, C20:4 (n-3)) and docosahexaenoic acid (DHA, C22:6 (n-3)) have been shown consistently in human studies. However, the effects of long chain marine fish oils on blood pressure are less consistent. One reason for the inconsistent effects of fish oils supplementation on blood pressure may relate to study design as is so often the case. However, another possibility is that genetic variation modifies the response to fish oils in the diet. Evidence for example suggests that the single nucleotide polymorphism (SNP) rs1378942 in the tyrosine kinase gene may be associated with blood pressure through its role in the regulation of sodium potassium pump activity.
Researchers have investigated the interactions of the rs1378942 genotype with fish oils in healthy subjects1. Subjects were randomly assigned to receive either an olive oil placebo capsule or 0.45, 0.9 or 1.8 grams per day EPA and DHA in a ration of 1.5:1, for 12 months. Before treatment at baseline, there was no association between the genotype of the subjects and their blood pressure. However, following the 12 months of the study significant associations were found between treatment groups and the systolic, diastolic, and mean arterial blood pressures. In particular, those subjects without a working copy of the rs1378942 gene showed significant decreases in systolic blood pressure, diastolic blood pressure and mean arterial blood pressure following consumption of the 1.8 grams per day of fish oils. Therefore non-carriers of the rs1378942 containing allele may be protected from cardiovascular disease through the consumption of fish oil, but those with the risk allele may not confer the same protective effects.
These results explain to some extent the inconsistent finding regarding fish oil supplementation and blood pressure. Gene nutrient interactions are common in human health and it is not always clear whether a nutrient will have a particular effect because of biochemical individuality. In this study those with a particular polymorphism in the gene that codes for a tyrosine kinase protein were not able to confer beneficial changes from fish oil supplements in terms of blood pressure changes. However, that is not to say they may not have benefited from the fish oil in other ways as the long chain marine fatty acids EPA and DHA have many different effects in human metabolism. It is interesting that the authors of this study did not measure the body weights of the subjects as body weight reductions are associated with blood pressure improvements and fish oils are known to induce weight loss effects. As to the question of whether fish oils lower blood pressure, yes they can, but the results will depend on biochemical individuality.