Omega-3 fatty acids are essential fats the body can’t make in large amounts. The two most studied, EPA and DHA, are found mainly in oily fish. A third, ALA, comes from plants such as flax, chia and walnuts, but the body converts only a small fraction of it into EPA and DHA.
What omega-3s do
They’re built into cell membranes throughout the body, including the brain and eyes, and play roles in inflammation and heart rhythm.
What the evidence shows
Eating fish is consistently associated with lower risk of heart disease. Many guidelines recommend about two servings of oily fish a week.
Supplements are a different story. Large trials, including the VITAL study, found that fish oil supplements in generally healthy people didn’t significantly reduce overall rates of heart attack, stroke or cancer.
Where supplements have clearer roles:
- High triglycerides: prescription-strength omega-3s lower triglycerides, and one purified form of EPA reduced cardiovascular events in people at high risk on statins.
- Rheumatoid arthritis: may modestly reduce joint stiffness and pain.
Evidence for depression, dry eyes and cognitive decline is mixed. A recent concern: some studies link higher-dose supplements with a small increased risk of atrial fibrillation, an irregular heart rhythm.
If you take a supplement
- Check the label for the amount of EPA and DHA, not just total fish oil.
- Choose third-party tested products to reduce concerns about contaminants and oxidation.
- Algae-based supplements provide EPA and DHA for people who don’t eat fish.
- Tell your clinician if you take blood thinners.
The bottom line
For most people, eating oily fish twice a week is a better-supported strategy than a supplement. Supplements make most sense for specific conditions, under medical guidance.