So you take a few fish oil capsules every day and eat fish once or twice a week. What is the blood and tissue level of omega-3 fatty acids generated by your habits?
A number of variables enter into the equation. For instance, if you take fish oil capsules, what is the concentration of omega-3 fatty acids? How well are they absorbed? After absorption, how effectively are omega-3 fatty acids incorporated into cell membranes?
Even if you take fish oil supplements, it is hard to know just how much you’ve increased blood levels. It is now possible to measure the amount of omega-3 fatty acids in your bloodstream, a value called the omega-3 index. Too little and you might still be at high risk for cardiovascular events.
The Omega-3 index and sudden cardiac death
Two large studies have demonstrated that higher omega-3 blood (the level in red blood cells, or RBCs) levels were associated with reduced likelihood of sudden cardiac death. The risk for sudden cardiac death was 10-fold higher for the lowest omega-3 RBC levels compared to the highest.
Harris WS 2008; adapted from Siscovick DS et al 1995 and Albert CM et al 2002
(The omega-3 Index was derived from whole blood omega-3 levels, which correlate with RBC omega-3 levels, and are thus “estimated.”)
What’s the average omega-3 RBC level for Americans? Most Americans have omega-3 RBC levels in the 2.5-4.0% range, consistent with the tallest bars at the left and associated with greatest risk for sudden cardiac death. People with heart disease can have levels less than 1%. Some authorities propose that this new measure be called the omega-3 index.
Subsequent studies have shown that the omega-3 index has greater power to discriminate who will have a heart attack or die from sudden cardiac death better than any other common laboratory measure of coronary risk, including LDL cholesterol, HDL cholesterol, triglycerides, total cholesterol to HDL ratio, homocysteine, and c-reactive protein.
Just as hemoglobin A1c offers a 3-month look into blood glucose levels, the omega-3 index reflects your long-term omega-3 intake. The quantity of RBC omega-3s also closely parallels the quantity of omega-3s in heart tissues.
What is an ideal omega-3 index?
The above studies relating RBC omega-3 levels and sudden cardiac death suggest that a level of 6.3-7.3% is associated with far fewer fatal events⎯but events are not eliminated at this level. Is there even greater benefit with levels higher than 6.3-7.3%?
A recent analysis of females from the Harvard School of Public Health suggested that RBC omega-3 levels as high as 8.99% were still associated with non-fatal heart attack (myocardial infarction), compared to 9.36% in those without heart attacks. This suggests that even higher levels are necessary to prevent non-fatal events.
Should we target 10%? 12%? Maybe higher? Any higher and we are toeing the level achieved by the Inuits, the “Eskimoes” of Greenland, northern Canada and Alaska who have been observed to have a low rate of heart disease.
What’s your omega-3 index?
The appreciation of the importance of omega-3 fatty acids marks one of the greatest health revelations of the last 50 years. We can now measure it.
The ability to measure the proportion of omega-3 fatty acids in red blood cells may provide yet another means for all of us to further reduce risk for cardiovascular events.
If you are interested in knowing your omega-3 index, we are now making the fingerstick test kits available by going here.