Supplements · 4 min read ·

Omega-3: fish on the plate or in a capsule?

Fish oil capsules are among the best-selling supplements. Do they protect the heart? And can flaxseed replace fish?

In a nutshell

1Three omega-3s

The name omega-3 mainly covers three fatty acids. Alpha-linolenic acid (ALA) comes from plants — most of all from flaxseed (about 23 g per 100 g), chia seeds (about 18 g) and walnuts (about 9 g).4 EPA and DHA come mainly from fish and seafood.2

Moderate evidence ALA → DHA: almost nothing Experiments with labelled fatty acids show that the body turns ALA into EPA only to a limited extent, and into DHA very little. Women do somewhat better than men, probably thanks to oestrogen.3

2How much you need

Strong evidence 250 mg a day of EPA and DHA combined — according to the European Food Safety Authority (EFSA), that is an adequate intake for adults for a healthy heart and blood vessels.1
Strong evidence 1–2 servings a week of fish and seafood are linked, according to EFSA, with a lower risk of dying from coronary heart disease in adults. In pregnancy (up to 3–4 servings a week) they are linked with better brain development of the child. More servings brought no extra benefit.2

3Do capsules help?

Strong evidence 25,871 people In the VITAL trial, men over 50 and women over 55 took 1 g of omega-3 a day, or a placebo, for about five years. The capsules did not reduce heart attacks, strokes and other major cardiovascular events, nor cancer.5
Strong evidence 45 studies, 143,693 people A Cochrane review: more EPA and DHA (mostly from capsules) has little or no effect on overall mortality. It does lower blood triglycerides, by about 15%, and may slightly reduce the risk of coronary heart disease.6

4What to watch out for

Strong evidence +25% atrial fibrillation A summary of 7 large trials with 81,210 people (average age 65): omega-3 capsules increased the risk of atrial fibrillation, the most common heart rhythm disorder. By 49% at doses above 1 g a day, by 12% at up to 1 g a day.7
Strong evidence up to 5 g a day EPA and DHA from supplements, up to 5 g a day combined, raise no safety concerns for adults according to EFSA — for example, they do not increase bleeding. This assessment dates from 2012, before the atrial fibrillation studies.8

Related articles: Fats.

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. EFSA NDA Panel (2010). Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol. EFSA Journal 8(3):1461. doi.org/10.2903/j.efsa.2010.1461
  2. EFSA NDA Panel (2014). Scientific Opinion on health benefits of seafood (fish and shellfish) consumption in relation to health risks associated with exposure to methylmercury. EFSA Journal 12(7):3761. doi.org/10.2903/j.efsa.2014.3761
  3. Burdge G. C., Calder P. C. (2005). Conversion of α-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. Reproduction Nutrition Development 45(5):581–597. doi.org/10.1051/rnd:2005047
  4. USDA ARS. FoodData Central, SR Legacy — alpha-linolenic acid (PUFA 18:3): flaxseed 22.8 g, chia seeds 17.8 g, walnuts 9.1 g per 100 g. fdc.nal.usda.gov
  5. Manson J. E. et al. (2019). Marine n−3 fatty acids and prevention of cardiovascular disease and cancer. New England Journal of Medicine 380:23–32. doi.org/10.1056/NEJMoa1811403
  6. Abdelhamid A. S. et al. (2020). Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 3:CD003177. doi.org/10.1002/14651858.CD003177.pub5
  7. Gencer B. et al. (2021). Effect of long-term marine ω-3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation 144:1981–1990. doi.org/10.1161/CIRCULATIONAHA.121.055654
  8. EFSA NDA Panel (2012). Scientific Opinion on the Tolerable Upper Intake Level of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). EFSA Journal 10(7):2815. doi.org/10.2903/j.efsa.2012.2815
  9. Arterburn L. M. et al. (2008). Algal-oil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. Journal of the American Dietetic Association 108(7):1204–1209. doi.org/10.1016/j.jada.2008.04.020

This is general information and does not replace a doctor. Food supplements are not medicines; buy them from reputable sellers. If you take blood thinners, ask your doctor about omega-3 supplements.