Omega-3 Evidence by Use: Heart, Triglycerides, Pregnancy, Brain and Eyes

Prescription medicines are a separate category

Some omega-3 products are approved prescription medicines. NCCIH notes that their composition is not the same as typical supplements, and that testing and regulation differ, so their effects may not be the same as those of supplements. [1] The FDA label for icosapent ethyl (a purified EPA ethyl ester) lists use alongside statin therapy to lower cardiovascular events in adults with raised triglycerides plus established heart disease or diabetes with other risk factors, and use with diet for triglycerides of 500 mg/dL or higher. [2] The FDA label for the EPA and DHA ethyl ester medicine lists only the high-triglyceride use and says its effect on cardiovascular mortality and morbidity has not been determined. [3] See Prescription omega-3 medicines vs over-the-counter supplements.

Evidence by use

1. First heart attack or stroke, general adults

   No clear benefit shown for this product and group

   VITAL: 25,871 US adults, 1 g a day of marine omega-3 vs placebo, median 5.3 years. Major cardiovascular events were not significantly lower (hazard ratio 0.92, 95% CI 0.80 to 1.06). [4]

2. First events in people with diabetes

   No benefit shown

   ASCEND: 15,480 adults with diabetes, 1-g capsules vs olive oil placebo, mean 7.4 years. Serious vascular events 8.9% vs 9.2% (rate ratio 0.97, 95% CI 0.87 to 1.08). [5]

3. Heart disease overall, all trials pooled

   Promising but limited

   Cochrane 2020 (86 trials, 162,796 people): little or no effect on all-cause death or cardiovascular events; possible slight reduction in coronary heart disease events (RR 0.91) and deaths (RR 0.90), low-certainty. [6]

4. Purified EPA in high-risk statin users

   Prescription-product trial; does not transfer to supplements

   REDUCE-IT: 8,179 adults, 4 g a day icosapent ethyl, median 4.9 years. Primary events 17.2% vs 22.0% on placebo (hazard ratio 0.75). [7]

5. EPA and DHA at 4 g a day vs corn oil

   No benefit shown for that product

   STRENGTH: 13,078 high-risk statin users. Primary events 12.0% vs 12.2% (hazard ratio 0.99); stopped early for low probability of benefit. [8]

6. Blood triglycerides (a biomarker)

   Established for the lab number

   Cochrane: EPA and DHA lowered triglycerides by about 15%, dose-dependent. AHA advisory: 4 g a day prescription products lowered very high triglycerides by 30% or more. [6][9]

7. Stroke

   No benefit shown

   Cochrane: little or no effect (RR 1.02, 95% CI 0.94 to 1.12). [6]

8. Pregnancy outcomes

   Promising, with a trade-off

   Cochrane 2018 (70 trials, 19,927 women): preterm birth under 37 weeks 13.4% vs 11.9%; under 34 weeks 4.6% vs 2.7%; pregnancy beyond 42 weeks probably increased 1.6% to 2.6%. [10]

9. Child brain development after use in pregnancy

   Limited

   A 15-trial review for the 2020 US Dietary Guidelines committee found limited evidence for cognition and insufficient evidence for other outcomes. [1]

10. Memory and cognitive decline

    Promising but limited

    A 2022 review of 33 studies suggested a protective effect in healthy people but no effect on cognition in people already diagnosed with Alzheimer's disease. [1]

11. Depression

    Insufficient

    A 2021 review of 35 studies (1,964 people): if there is an effect it may be too small to matter; quality low or very low. [1]

12. ADHD in children

    No benefit shown

    A 2023 review of 36 studies found no evidence that symptoms are likely to improve. [1]

13. Dry eye

    Mixed, leaning no benefit

    DREAM: 535 people, 3,000 mg a day EPA and DHA vs olive oil placebo for 12 months; no significant difference in symptom score. A 2022 review of 8 small studies suggested possible symptom improvement, with bias concerns. [11][1]

14. Macular degeneration

    No benefit shown

    AREDS2 (over 4,000 people): adding EPA and DHA gave no additional benefit. [1]

15. Rheumatoid arthritis

    Insufficient

    Reviews of diets rich in omega-3 fats found lower pain, but one review judged the evidence low. These were foods, not capsules. [1]

Deeper pages: heart attacks and strokes, high triglycerides, dry eye, pregnancy, depression, memory and why trials disagree.

Notes on reading the table

• Heart disease. Trial results differ because the products, amounts, comparators and participants differ. One pooled analysis of 13 trials (127,477 people) reported lower risk of heart attack and coronary death. [12] An earlier pooled analysis of 10 trials (77,917 high-risk people, EPA amounts 226 to 1,800 mg a day) found no significant link with coronary death, heart attack or major vascular events. [13] Both are summarized on the heart attacks and strokes page.
• Food versus capsules. The NHS advises at least 2 portions of fish a week, including 1 of oily fish, and says long-chain omega-3 can help keep the heart healthy. [14] The Cochrane review notes there is little evidence of effects of eating fish in trials. [6] See omega-3 supplements vs eating fish.
• Pregnancy. The NHS advises avoiding fish liver oil supplements in pregnancy unless a GP advises otherwise, because of their vitamin A. [14] US advice for pregnancy and breastfeeding is 8 to 12 ounces of lower-mercury seafood a week. [1] Ask your maternity provider before any omega-3 product; see Pregnancy and breastfeeding.
• Eyes. AREDS2 is covered with antioxidant evidence by use.
• Mental health. Depression can be serious. Supplements are not a substitute for care from a clinician; in the US, 988 is the Suicide & Crisis Lifeline, and 911 is for emergencies.