Omega-3 Index: A Blood Test Most People Never Take

The omega-3 index measures the combined percentage of EPA and DHA, the two main long-chain omega-3 fatty acids, as a proportion of total fatty acids in red blood cell membranes. Because red blood cells turn over roughly every 120 days, this test reflects your actual omega-3 status over the preceding months rather than relying on self-reported fish or supplement intake, which is notoriously unreliable.

Population studies have found associations between a higher omega-3 index and lower risk of cardiovascular events, and some researchers have proposed it as a risk marker on par with traditional cardiovascular risk factors. Most people who don't regularly eat fatty fish or supplement with fish oil test in a range researchers consider suboptimal, often without realizing it, since there's no way to estimate your own index from diet alone.

Why this matters for tracking: unlike most dietary questions, omega-3 status can be directly measured with a simple blood test rather than guessed at, making it one of the more objectively trackable nutrition-related biomarkers.