DHA increases the Omega-3 Index more than EPA

DHA contributes more than EPA to increasing the Omega-3 Index, a parameter useful for assessing cardiac risk, which indicates the percentage of EPA and DHA in the membranes of red blood cells. In particular, the increase in the Omega-3 Index is significantly greater after supplementation with 2.7 grams per day of DHA compared to the same amount of EPA.

This was discovered by researchers at the University of Quebec (Canada) and reported in the journal Prostaglandins, Leukotrienes and Essential Fatty Acids.

Omega-3 Index and cardiovascular risk

Several studies in recent years have aimed to determine the association between polyunsaturated fatty acid consumption and cardiovascular risk. Omega-3 EPA and DHA can modulate a variety of risk factors such as blood lipid concentration and type, blood pressure, inflammation, platelet aggregation, and possess significant antiarrhythmic action. Fatty fish from cold seas and marine-derived dietary supplements are the main sources of EPA and DHA. Although recent experimental evidence suggests EPA and DHA may have different effects on blood lipids and inflammatory signaling molecules, the evidence is limited, and most studies so far have evaluated these effects using mixtures of EPA and DHA in various forms and proportions. Little is known about the specific effects of EPA and DHA on biological processes related to cardiometabolic health—that is, diseases of both the heart and metabolic disorders like diabetes. The fatty acid composition of cell membranes influences their physicochemical properties and organ functions. The Omega-3 Index is the sum of EPA and DHA in red blood cell membranes and is expressed as a percentage of these two fatty acids relative to total membrane fatty acids; it reflects tissue composition, including the heart. Based on epidemiological research on the link between sudden cardiac death risk—an unexpected death due to cardiac causes—and omega-3 percentage in red blood cells, scientists have concluded:

• If the Omega-3 Index is < 4%, there is a high probability of sudden cardiac death
• If the Omega-3 Index is between 4% and 8%, the risk is moderate
• If the Omega-3 Index is > 8%, the risk is low

A very high Omega-3 Index, between 8-12%, has been associated with lower coronary disease risk and mortality in epidemiological studies.

Omega-3 Index: greater increase with DHA

The aim of this study was to compare the effects of high doses of EPA and DHA on the Omega-3 Index, a parameter modifiable by diet and supplementation. While scientific evidence suggests DHA may be more potent than EPA in modifying cardiometabolic risk, their respective impacts on the Omega-3 Index had not been carefully examined. According to the researchers, this is the first study of its kind to demonstrate that the increase in the Omega-3 Index is significantly greater after supplementation with 2.7 grams per day of DHA compared to a comparable dose of EPA.

Research details

To reach these conclusions, scientists analyzed data from 154 men and women with abdominal obesity and inflammation who were assigned one of three treatments: 2.7 grams per day of EPA; 2.7 grams per day of DHA; or 3 grams per day of corn oil (lacking EPA and DHA) for 10 weeks. The fatty acid composition of red blood cell membranes and the Omega-3 Index were assessed at the start and end of each treatment. Analysis results showed that the Omega-3 Index of participants receiving DHA increased on average by 5.6%, compared to a 3.3% increase in those who consumed EPA. Based on previous studies on fatty acid metabolism in men and women, researchers also investigated potential sex differences in Omega-3 Index increase, observing a greater increase in EPA and DHA percentages in men compared to women.

A preliminary study opening the way to further investigations

EPA and DHA supplements are recommended for secondary prevention of cardiovascular diseases or for management of plasma triglycerides. Although a high Omega-3 Index is associated with lower cardiovascular disease risk and mortality, further research will be needed to compare the effects of different omega-3s on this clinical tool useful for cardiovascular risk management. "The increase in the Omega-3 Index is greater with the addition of high-dose DHA than EPA, which is consistent with DHA’s greater ability to modulate cardiometabolic risk factors," stated the study authors. "The extent to which differences between EPA and DHA influence long-term cardiovascular risk must be investigated in future studies," they concluded. Harry Rice, Vice President of the EPA and DHA organization (GOED), shared the same view and commented on the study’s conclusions, stating that the well-designed and conducted Canadian research provides a solid foundation for further studies, but is not yet sufficient to encourage people to choose different supplements. Until it is determined whether differences in the Omega-3 Index relate to cardiovascular outcome risk, such changes would be premature.

Source: J. Allaire et al. Supplementation with high-dose docosahexaenoic acid increases the Omega-3 Index more than high-dose eicosapentaenoic acid. Prostaglandins, Leukotrienes and Essential Fatty Acids (PLEFA).