Writing in the Journal of Clinical Lipidology, the team reported on findings from the 2,500 participants from the Offspring cohort of the Framingham Heart Study - finding that omega-3 index had a significant association with four of the five major outcomes (incidence of coronary heart disease (CHD), CVD and total and CVD mortality).
The study was conducted as a partnership between Boston University (the academic home of the Framingham Heart Study), the Global Organization for EPA and DHA omega-3 (GOED), and Dr. William Harris, President and CEO at Omegaquant, LLC.
Omega-3 index is the total of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content of red blood cell (RBC) membranes. A value of over 8% is categorised as optimal or low-risk, while levels between 4-8% are classed as intermediate-risk, and below 4% as high-risk.
The study’s main outcome identified that risk of death was around a third lower in participants in the highest quintile of omega-3 index, compared with those in the lowest quintile.
“Those in the highest (>6.8%) compared to those in the lowest omega-3 index quintiles (<4.2%) had a 34% lower risk for death from any cause and 39% lower risk for incident CVD,” commented lead author Dr. Harris.
Better predictor than cholesterol
An additional finding of the study was that omega-3 index was a better predictor than cholesterol for risk for death and some measures of CVD.
“A novel finding of this study was that the omega-3 index was better than cholesterol when it came to predicting risk for death,” said Harris.
"We all know that the serum cholesterol level is a major risk factor for CHD, and since the latter is a major cause of death in the Western world, it would be reasonable to expect that a high cholesterol level would portend higher risk for premature death.
"This did not turn out to be the case here. When baseline serum cholesterol levels were substituted for the omega-3 index in the same multi-variable models, the former was not significantly associated with any of the tracked outcomes whereas the latter was related to 4 of the 5 outcomes assessed."
The results merit further investigations in younger populations and comparisons with other CVD risk predictors, suggested Harris.
“This has not been examined in previous studies, so we are interested in asking this question in other populations, as well as comparing the omega-3 index to other predictors of disease risk (LDL-cholesterol, HDL-cholesterol, C-Reactive Protein, blood pressure, etc).”
The participants (average age 66) were all free of CVD at baseline. The scientists collected data on 18 demographic and CVD risk covariates. Baseline measurements were obtained of RBC EPA and DHA, together with total cholesterol.
The participants were followed up over a median period of 7 years, during which incidence of death (total, CVD related, cancer and other), stroke, CVD, and CHD were recorded. Incidence of the various outcomes (adjusted for confounding covariates) was correlated against omega-3 index and against total cholesterol.
Implications for omega-3 intake
As the study was observational, it was not possible to conclude that raising the omega-3 index would have heart benefits or prolong life, the researchers cautioned.
Nevertheless, they thought it productive to provide an estimates of how much additional EPA + DHA would be needed to move an individual from the lowest (median =3.7%) to the highest quintile (median=7.8% of omega-3 index.
Based on a previous dose-response study, the scientists estimated that an additional 1300 mg/d would achieve this increase. Either eating 100g of farmed salmon daily, or consuming four standard fish pills per day (typical EPA +DHA content ~330 mg/pill) could achieve the target.
Nevertheless, fish consumption is the preferred way of improving omega-3 index, recommended Harris.
“The best evidence we have is that it is the dose of EPA+DHA that is most important in determining the omega-3 index, whether that comes from fish or supplements (fish oil, krill oil, algal oil).
“As a nutritionist, however, I would always recommend oily fish first since fish provides other important nutrients, and when people are eating fish, they are not eating other types of meat that would not be as good for them (beef, pork, etc).
Case for wider Testing?
Harris suggested that routine testing of omega-3 index could be beneficial to the health of a wide range of population groups.
"Other studies have shown that omega-3 levels predict risk for death in people a full decade older, and it’s only reasonable to conclude that addressing a low omega-3 index in younger people make sense.
“A case can be made for testing people virtually across the entire range of ages, from pregnant mothers to grade school children to teenagers and on up. The sooner one can achieve healthy omega-3 index levels, the better in the long run.
"If cholesterol is considered important to test, then the omega-3 index should be too,” Harris concluded.
Source: Journal of Clinical Lipidology
Published online, doi: 10.1016/j.jacl.2018.02.010
“Erythrocyte long-chain omega-3 fatty acid levels are inversely associated with mortality and with incident cardiovascular disease: The Framingham Heart Study”
Authors: William S. Harris, Nathan Tintle, Mark R. Etherton, Ramachandran S. Vasan