Omega-3 Index
The EPA and DHA content of red blood cell membranes, expressed as a percentage of total fatty acids. Because red cells turn over slowly, the index reflects omega-3 status across roughly the preceding three to four months rather than what happened at dinner — a real advantage over dietary recall. Those fatty acids incorporate into cell membranes, affecting fluidity, electrical stability and inflammatory eicosanoid production.
Harris WS, von Schacky C. “The Omega-3 Index: a new risk factor for death from coronary heart disease?” Preventive Medicine 2004;39:212–220 proposed the index and found that an index ≤4% carried substantially higher coronary heart disease death risk than ≥8%. Subsequent cohort data are broadly supportive. Outcome-trial evidence for supplementing specifically to raise the index is mixed: VITAL, using low-dose marine omega-3 in a general population, was neutral for major cardiovascular events, while REDUCE-IT, using high-dose purified EPA in higher-risk patients, showed benefit. A reasonable status marker — but “test and target a number” has not itself been proven in a trial to change outcomes for an average-risk person.
Harris WS, von Schacky C. Prev Med. 2004. PubMed: PMID 15208005