What are omega-3 fatty acids and where do they come from?
ALA (alpha-linolenic acid) is abundant in plants like flaxseed, perilla oil and walnuts, and the body converts only a small share into EPA and DHA. EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are rich in fatty fish such as mackerel, salmon and sardines, and in algae. DHA is a major component of cell membranes in the brain and retina.
What they do in the body
Omega-3s build cell membranes and serve as raw material for compounds that regulate inflammation (eicosanoids, resolvins and others). High doses of 2–4 g a day fairly consistently lower blood triglycerides by reducing their production in the liver.
Results from large trials
- VITAL (2019): 1 g a day in 25,871 generally healthy adults didn't clearly reduce major cardiovascular events or cancer.
- REDUCE-IT (2019): 4 g of purified EPA cut events by 25% in high-risk people with elevated triglycerides, though debate continues over whether the mineral-oil placebo skewed results.
- STRENGTH (2020): 4 g of EPA+DHA showed no benefit over corn oil and was stopped early.
As these show, randomized controlled trial results vary with the population, dose, formulation and comparator. A meta-analysis also found that high doses slightly raise the risk of atrial fibrillation (Gencer et al., 2021).
In practice
Many professional groups, including the American Heart Association, recommend eating fish at least once or twice a week. Except for prescription use in people with high triglycerides, supplements haven't clearly been shown to prevent disease in healthy people. If you take blood thinners, talk to your doctor before taking high doses. For the other pillar of lipid management, see LDL cholesterol.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Is eating fish better than taking fish oil pills?
- For most healthy people, guidelines favor eating fatty fish once or twice a week; supplements have clear benefit mainly for lowering high triglycerides under a doctor's care.
Sources reviewed: 2026-10-25
References
- Manson, J. E., et al. (2019). Marine n−3 fatty acids and prevention of cardiovascular disease and cancer. New England Journal of Medicine, 380(1), 23–32.
- Bhatt, D. L., et al. (2019). Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia. New England Journal of Medicine, 380(1), 11–22.
- Nicholls, S. J., et al. (2020). Effect of high-dose omega-3 fatty acids vs corn oil on major adverse cardiovascular events. JAMA, 324(22), 2268–2280.
- Gencer, B., et al. (2021). Effect of long-term marine ω-3 fatty acids supplementation on the risk of atrial fibrillation. Circulation, 144(25), 1981–1990.