Omega-3 fatty acids have had a prominent place in the conversation around health promotion and disease prevention—especially CVD prevention—for decades. While alpha-linolenic acid (ALA) is found in plant sources like flaxseeds and walnuts, the most clinically significant omega-3s are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are primarily sourced from marine life.
Initially popularized by epidemiological observations of cardiovascular health among populations with high dietary fish consumption, the scientific understanding of these essential fats has evolved and moved beyond a generalized view of “fish oil.” Modern research is increasingly focused on the distinct biological roles of specific fatty acids, optimal dosing strategies, and the nuanced ways these molecules interact with human physiology.
Although both EPA and DHA are long-chain polyunsaturated fatty acids, they exhibit distinct physical properties and biological behaviors. DHA is highly concentrated in the structural membranes of the brain and retina, where its molecular shape promotes membrane fluidity—a characteristic vital for cellular signaling and neuronal health, while EPA is not stored in brain tissue to the same extent. Instead, it plays a critical role in systemic inflammatory pathways. Furthermore, both EPA and DHA serve as precursors to a class of signaling molecules known as specialized pro-resolving mediators that actively signal the immune system to halt inflammation and begin tissue repair.1,2
As research continues to clarify the clinical applications of omega-3s, the most recent data from clinical trials and comprehensive meta-analyses have challenged several long-held assumptions, including that not all omega-3 supplements yield identical effects. One reason is that standardized dose doesn’t have the same physiological effects on each individual.
This is why, when assessing cardiovascular risk and dietary fat intake, clinical guidelines and nutritional science increasingly point toward the Omega-3 Index. Unlike standard dietary assessment tools, this biomarker offers a more precise view of an individual’s longer-term lipid status, which can make it a valuable tool in evidence-based nutrition counseling.
What Is the Omega-3 Index?
The Omega-3 Index is defined as the combined percentage of EPA and DHA found in red blood cell membranes.3 Because red blood cells have an approximately 120-day lifespan, assessing their membrane composition reflects long-term omega-3 intake rather than the omega-3 content of recent meals. This makes the index functionally similar to how hemoglobin A1c provides a long-term picture of glucose homeostasis, allowing clinicians and researchers to move beyond simple dietary estimates and measure actual physiological assimilation.4
Researchers first proposed the Omega-3 Index as an independent, graded risk factor for coronary heart disease mortality in 2004.3 More recently, a 2024 systematic meta-analysis of observational studies documented that higher EPA and DHA erythrocyte membrane levels are associated with a 45% reduction in risk of sudden cardiac death.5 Additional results from epidemiological and clinical studies, including the Framingham Heart Study,6 have found a strong inverse relationship between the index “score” and the risk of sudden cardiac death and other cardiovascular events:
• High risk: An index of 4% or lower is associated with the least cardioprotection and is typical of standard Western diets lacking in seafood.
• Intermediate risk: An index between 4% and 8%.
• Low risk: An index of 8% or greater is associated with the highest level of cardioprotection and significantly lower cardiovascular risk. In populations that consume high amounts of fatty fish, the average population Omega-3 Index naturally sits around 8% to 9%, which correlates with significantly lower rates of cardiovascular deaths.4,7
According to NHANES data from August 2021 to August 2033, only 2.1% of the United States population age 6 or older had an Omega-3 Index above 8%, 43.8% were between 4% and 8%, and 54.1% had an index below 4%. The average score overall was 4.12%. Percentages tended to be higher with age and among certain demographics, including females, non-Hispanic Asians, people above the poverty line, those with education beyond high school, nonsmokers, and people taking polyunsaturated fatty acid supplements.8
Clinical Utility and Individualized Care
In practice, advising patients and clients to simply “eat more fish” or take a standard fish oil supplement often yields unpredictable physiological results. Recent research has found that biological responses to omega-3 intake are highly variable. Factors such as an individual’s baseline omega-3 status and body composition can significantly influence how efficiently dietary EPA and DHA are incorporated into red blood cells,9 as can the bioavailability of omega-3s in foods, fortified foods and supplements.2
For example, an eight-week intervention providing specific amounts of fatty fish showed that a person’s baseline status heavily dictated their resulting shift in the Omega-3 Index. This reinforces what dietitians know: that standardized dietary advice does not automatically produce standardized metabolic outcomes.9 It also highlights the importance of personalized, evidence-based nutrition interventions over blanket prescriptions or rigid dietary rules.
While the legitimacy of the Omega-3 Index is backed by numerous peer-reviewed papers, it’s not yet a routine part of a standard annual physical or basic lipid panel, largely due to cost and the lack of universal standardization among all independent labs. Also, there is still some uncertainty about the preventive role of omega-3s in CVD, in part due to the lack of baseline EPA/DHA measurements in many studies.2
Still, research on the Omega-3 Index continues, and is being expanded to research on numerous other health conditions, including type 2 diabetes10 and psychiatric diseases,11 with results suggesting that higher tissue levels of omega-3s have a positive effect on metabolic and physiological processes beyond the heart.12 Results of a study published in 2026 found that, among COVID patients, a higher modified Omega-3 Index (measured in the blood rather than in the erythrocytes) was associated with lower odds of death.13
The Bottom Line
The fact that NHANES data shows that most people in this country have Omega-3 index scores that are far from optional means that dietitians have work to do in helping patients and clients get more omega-3s into their diets.
Even though the index isn’t a standard part of lipid panels, direct-to-consumers Omega-3 Index tests are available. However, it’s worth noting that there’s currently a commercial monopoly on the most popular testing kits. Also, when a patient knows their index score, the dose required to move the needle varies wildly—one individual might reach the 8% target with 1,000 mg of EPA/DHA daily, but another might require a much higher dose to achieve the exact same index,14 which would make repeat testing useful. So while research on the Omega-3 Index is more than just promising, until it becomes a standard part of clinical practice, it’s utility to practitioners remains also far from optimal.
— Carrie Dennett, MPH, RDN, is editor of Today’s Dietitian.
References
1. Omega-3 fatty acids: fact sheet for health professionals. National Institutes of Health Office of Dietary Supplements website. https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/. Updated August 22, 2025.
2. Egalini F, Riccio E, Grasso M, Nelva A, De Geronimo V. Omega-3 polyunsaturated fatty acid formulations in cardiovascular prevention: balancing clinical efficacy, safety, and environmental sustainability. Nutrients. 2026;18(15):2538.
3. Harris WS, Von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease? Prev Med. 2004;39(1):212-220.
4. von Schacky C. Omega-3 index and cardiovascular health. Nutrients. 2014;6(2):799-814.
5. Kim JY, Kong SYJ, Jung E, Cho YS. Omega-3 fatty acids as potential predictors of sudden cardiac death and cardiovascular mortality: a systematic review and meta-analysis. J Clin Med. 2024;14(1):26.
6. Filipovic MG, Reiner MF, Rittirsch S, et al. Blood omega-3 fatty acids are inversely associated with albumin-creatinine ratio in young and healthy adults (the Omega-Kid study). Front Cardiovasc Med. 2021;8:622619.
7. Harris WS, Del Gobbo L, Tintle NL. The Omega-3 Index and relative risk for coronary heart disease mortality: estimation from 10 cohort studies. Atherosclerosis. 2017;262:51-54.
8. Powers CD, Sternberg MR, Mineva EM, et al. Over half of the united states population had an undesirably low omega-3 index based on erythrocyte membrane measurements: results from the cross-sectional NHANES from August 2021 to August 2023. Curr Dev Nutr. 2026;10(6):107715.
9. Richardson CE, Krishnan S, Gray IJ, Keim NL, Newman JW. The Omega-3 Index response to an 8-week randomized intervention containing three fatty fish meals per week is influenced by adiposity in overweight to obese women. Front Nutr. 2022;9:810003.
10. Ma MY, Li KL, Zheng H, Dou YL, Han LY, Wang L. Omega-3 index and type 2 diabetes: systematic review and meta-analysis. Prostaglandins Leukot Essent Fatty Acids. 2021;174:102361.
11. Antao HS, Sacadura-Leite E, Bandarra NM, Figueira ML. Omega-3 index as risk factor in psychiatric diseases: a narrative review. Front Psychiatry. 2023;14:1200403.
12. Harris WS. Recent studies confirm the utility of the omega-3 index. Curr Opin Clin Nutr Metab Care. 2025;28(2):91-95.
13. Bischofová S, Měřínská Z, Beňovská M, et al. Association of omega-3 fatty acids (EPA, DHA, DPA) and vitamin D with mortality and morbidity outcomes in COVID-19 patients: the COMED study. Front Nutr. 2026;13:1892752.
14. Dempsey M, Rockwell MS, Wentz LM. The influence of dietary and supplemental omega-3 fatty acids on the omega-3 index: a scoping review. Front Nutr. 2023;10:1072653.