To compare fish-oil supplements, look for the milligrams of EPA and DHA—not just the larger number for total fish oil. And while omega 3 supplements heart health claims are common, ordinary supplements have not been shown to reliably prevent heart disease. Prescription omega-3 medicines are different products, used for specific medical reasons.
Read The EPA And DHA Amounts, Not Just “Fish Oil”
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the long-chain omega-3 fats found in fish oil. The total fish oil amount includes these fats and other oil components; it does not tell you how much EPA and DHA you get.
For example, a hypothetical serving might list 1,000 mg (1 g) of fish oil, with 180 mg EPA and 120 mg DHA. That serving provides 300 mg of EPA plus DHA—not 1,000 mg. Add the two amounts to compare products, and check whether the serving is one capsule or several. A label may list amounts per serving rather than per capsule.
There is no established recommended daily amount of EPA and DHA for everyone. So a higher number on a label is not automatically a better choice, and the dose used in a trial or prescription should not be treated as a general supplement target. Cod liver oil also contains vitamins A and D, which vary by product; check those amounts as well.
Omega 3 Supplements Heart Health: What Trials Tell Us
Taking a typical fish-oil supplement is not a proven way for everyone to prevent a first heart attack or other cardiovascular event. The results depend on who was studied and which product they took. The NIH Office of Dietary Supplements notes that some analyses have found small reductions in certain coronary events, but results for outcomes such as stroke are less consistent. Seafood and supplements are not interchangeable: the health benefits associated with eating seafood may involve other nutrients or the foods it replaces.
Two large trials help explain why a broad “fish oil protects your heart” claim can mislead. In VITAL, a primary-prevention trial involving men aged 50 and older and women aged 55 and older, a combination of EPA and DHA did not significantly reduce the main cardiovascular outcomes. ASCEND tested a similar combination in people with diabetes but no known cardiovascular disease; it also found no significant reduction in serious vascular events. These results do not prove that every omega-3 product has no effect, but they do not support relying on ordinary mixed fish-oil supplements to prevent heart disease.
REDUCE-IT studied something different: prescription-strength, purified EPA (icosapent ethyl), taken at 4 g per day alongside statin treatment by people at elevated cardiovascular risk with high triglycerides. It found fewer major cardiovascular events than the placebo group. That result applies to the specific prescription medicine and the high-risk patients studied; it cannot be assumed for a shop-bought EPA-and-DHA supplement.
Supplements And Prescriptions Are Not Substitutes
Prescription omega-3 medicines are standardized drugs tested for safety and effectiveness for specific uses. Some are prescribed with dietary measures to lower very high triglycerides. In the United States, approved products and indications differ: they include medicines for severe hypertriglyceridemia, and icosapent ethyl also has a cardiovascular-risk-reduction indication for certain high-risk patients taking statins. Eligibility and approvals vary by country, so ask a clinician or pharmacist about the rules where you live.
Over-the-counter supplements are not equivalent to those medicines. In the United States, the FDA regulates dietary supplements differently from prescription drugs; they do not undergo the same premarket approval process for treating disease. Product formulations and declared EPA and DHA amounts can vary. A supplement label therefore cannot establish that a product will lower your triglycerides like a prescription medicine or deliver the cardiovascular outcomes seen in a drug trial.
If you are comparing plant and marine omega-3s, remember that flaxseed provides ALA, a different omega-3 from EPA and DHA. Learn how plant and fish omega-3s differ.
When To Get Medical Advice
If your concern is high triglycerides, a blood-test result or heart-risk assessment is a better starting point than choosing a supplement dose. Do not replace prescribed treatment with fish oil. High doses of omega-3s may interact with medicines such as anticoagulants, so discuss supplements with a clinician or pharmacist if you take medication or are considering a high dose.