- Zhang et al. Omega-3 Polyunsaturated Fatty Acids Intake and Blood Pressure: A Dose-Response Meta-Analysis of Randomized Controlled Trials. Originally published 1 Jun 2022
The positive effect of polyunsaturated omega-3 fatty acids on our cardiovascular system has been researched for some time. The two long-chain forms eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular have attracted the interest of scientists. They are found in abundance in fish products and are held responsible for the very low rate of cardiovascular diseases among the Inuit people, who mainly eat fish.
EPA and DHA are supposed to achieve this, among other things, through their blood pressure-lowering effect. However, in randomised controlled trials (RCTs) in which both omega-3 fatty acids were supplemented individually or in combination, no clear effect on blood pressure was found. Recent meta-analyses also found no association between EPA/DHA and blood pressure.
A group of researchers led by Xin Zhang from the University of Macau in China attributes these results to the fact that a linear dose-response relationship between the intake of omega-3 fatty acids and blood pressure reduction was previously assumed. If this were not the case, the statistical models of the previous studies might not have reflected this correctly.
Therefore, Zhang's team conducted their own meta-analysis, in which they used a statistical method that can also represent non-linear relationships between two variables. The meta-analysis included 71 RCTs with a total number of more than 4,900 subjects who were administered EPA and DHA and had their blood pressure measured during the course of the study. In most studies, both omega-3 fatty acids were given in doses of 1gr to 6gr In only two studies were up to 15gr given. Only two studies used up to 15gr The administration was either in the form of EPA or DHA. They were given either in the form of supplements or in a diet containing fish. The average study duration was 10 weeks. Olive oil or another vegetable oil was usually used as a placebo.
The research team found a non-linear relationship between the intake of EPA/DHA and blood pressure in the overall population. Taking both omega-3 fatty acids up to a dose of 3gr had a positive effect on systolic and diastolic blood pressure, lowering systolic blood pressure by about 2.6 mmHg and diastolic blood pressure by about 1.7 mmHg.
In contrast, a higher dose was no longer associated with an antihypertensive effect. Subgroup analyses showed that this was particularly true for normotensive and younger patients (under 45 years).
In contrast, a linear dose-response relationship was found in older people and those with existing hypertension or increased lipid levels. In other words, a higher dose of DHA/EPA could also further lower blood pressure.
In summary, the study shows that there is a rather complicated relationship between the combined administration of EPA and DHA and the lowering of blood pressure. In largely healthy individuals (young, normotensive, normal lipid levels), there appears to be an optimal dose of 3gr for omega-3 fatty acid supplementation to lower blood pressure. In older and pre-diseased individuals (hypertensive, elevated lipid levels), on the other hand, even higher doses than 3gr seem to have a positive effect on blood pressure.
But how do these different effects come about? The scientific team suspects that pre-diseased individuals may metabolise the omega-3 fatty acids differently and also benefit from other pleiotropic effects, such as lowering triglycerides, influencing inflammatory responses and modulating heart rate. Future studies should take a closer look at this.
For everyday clinical practice, it can be taken away that for most patients the combined administration of EPA and DHA in a dose of 3gr seems to be optimal for lowering blood pressure. But they should not be prescribed lightly, as the increased risk of atrial fibrillation and bleeding must also always be taken into account, which has been described in previous studies.