There has been controversy in recent years about the relationship between omega-3 fatty acids and risk for heart disease, fatal and non-fatal. A new paper published in JAMA (June 2016) by Del Gobbo et al.
pooled individual patient data from 19 cohorts, which included over 45,000 patients, and compared their risk for fatal and non-fatal heart disease as a function of blood omega-3 levels.
Unfortunately, not all studies used the same test for omega-3: some used plasma, others plasma phospholipids (PL) or cholesteryl esters (CE), and yet others used red blood cells (RBCs) or adipose tissue. How to make sense of all these different measures? The authors simply compared risk for disease between the highest and lowest quintiles (Q) for all markers, which is reasonable since these all inter-correlate reasonably well.
What did they find?
Upper quintiles of EPA and DHA were associated with a lower risk of non-fatal myocardial infarction ([MI]; Q5 vs Q1 comparison: relative risk [RR] EPA, 0.71 [95% CI,0.56-0.90] vs RR DHA, 0.87 [95% CI, 0.78-0.97]). Top quintiles of DPA and DHA were associated with a lower risk of fatal coronary heart disease ([CHD]; RR DPA, 0.76 [95%CI, 0.65-0.90] vs RR DHA, 0.77 [95%CI, 0.64-0.89]). Note: if the 95% confidence interval [CI] does not include 1, then the effect is considered significant. So, EPA was more strongly predictive of reduced risk for non-fatal MIs than was DHA (even though both were statistically significant), whereas DHA (but not EPA) was associated with risk for fatal CHD events.
What the authors did not do was to convert their various blood measures to the estimated Omega-3 Index
. We, therefore, undertook this task using data from our lab. We have generated equations to translate the EPA+DHA level in whole plasma, PL and plasma CE to RBC phospholipids (i.e., the Omega-3 Index). The equations for plasma PL and CE were derived using data from 50 random subjects, and for plasma, data from 2,312 subjects in a large ongoing randomized controlled trial. The correlation coefficients with the Omega-3 Index for these three plasma compartments were 0.92, 0.83 and 0.90, respectively. So, the Omega-3 Index could be reasonably accurately estimated from these other metrics.
When we calculated the average quintile values across all these studies for the Omega-3 Index, the lowest quintile Index was 4.5%
and highest was 7.8%
. Since people with an Omega-3 Index in the lowest quintile were at the highest risk and those with an Omega-3 Index in the highest quintile were at the lowest risk for cardiac events, these data provide strong confirmation to the 4% and 8% cut-points for “undesirable” and “desirable” Omega-3 Index targets that were proposed by Harris and von Schacky in 2004
and used by OmegaQuant.