Conflicting nutrition-health studies can give you cognitive whiplash.

And recent clinical trials testing omega-3 fish oil's effects on heart-related health risks conveyed conflicting, confusing conclusions.

The overall picture regarding the effects of fish-rich diets — and diets high in seafood-source omega-3 fats — on heart health is quite positive.

For example, two recent reviews of the epidemiological (population study) evidence found consistent links between fish-rich diets and reduced risks for heart disease and its adverse outcomes (Wang C et al. 2006; Zheng J at Al 2012).

That said, epidemiological studies can only reveal statistical correlations between foods or nutrients and health — they can’t prove cause-effect relationships between them.

While clinical trials can verify the health effects of specific foods or nutrients, that’s only true if they're well-designed, sufficiently large and lengthy, and their results are confirmed by other high-quality trials.

Different trials and clinical-evidence reviews have come to different conclusions, and two recent clinical-evidence reviews didn’t conclude that supplemental fish oil significantly reduce cardiovascular risks (Abdelhamid AS et al. 2018; Aung T et al. 2018).

However, many of the clinical trials included in those reviews had stacked the deck, because they involved heart patients already taking statins and other heart drugs — making it unlikely that fish oil would produce measurable additional benefits.

Many reviews of the clinical evidence have focused on such “stacked-deck” trials, making their negative conclusions about the value of fish oil entirely predictable and sadly misleading.

That very flaw undermined the credibility of the two recent reviews that came to negative conclusions about the heart-value of fish oil, which were published prior to publication of three clinical trials of particularly high quality — called ASCEND, VITAL, and REDUCE‐IT — all of which concluded that omega-3 fish oil reduced either single or multiple cardiovascular risks.

For more on the REDUCE‐IT and VITAL trials, see Omega-3s’ Heart Value Vindicated in Long, Large Clinical Trial and Omega-3s Score 2nd Big Heart Win.

A new review of the clinical evidence — the first to include those three recent, large, high-quality trials — concluded that fish oil produces substantial reductions in the risk for heart disease and its adverse outcomes.

New evidence review is the most reliable to date
The new review — a sophisticated type of evidence review known as a meta-analysis — comes from researchers at the Harvard School of Public Health and Brigham and Women’s Hospital (Hu Y, Hu FB, Manson JE 2019).

Advantages and findings of the new review
These were the key points stressed by the authors of the new evidence review, in their own words:

  • We updated previous meta‐analyses by adding three recent large randomized controlled clinical trials, increasing sample size by 64%.
  • Marine omega‐3 supplementation significantly lowered risk for most cardiovascular end points, even after excluding a trial testing very high‐dose supplementation.
  • Greater cardiovascular benefits may be achieved at higher doses of marine omega‐ 3 supplementation.

The 13 clinical trials covered by the new review involved 127,477 people — 60% male, 40% female, average age 64.3 years — and lasted an average of five years.

Because the review encompassed the three recent trials mentioned above — ASCEND, VITAL, and REDUCE‐IT — it covered 64% more trial participants than the largest prior review.

After conducting their analysis, the Boston-based team concluded that people who received omega-3 fish oil capsules enjoyed significantly reduced risks for cardiovascular disease (CVD), coronary heart disease (CHD), and their adverse outcomes:

  • Reduced risk of a heart attack by 8%.
  • Reduced risk of dying from CHD by 8%.
  • Reduced risk of dying from CVD by 7%.
  • Reduced risk of developing CHD by 5%.
  • Reduced risk of developing CVD by 3%.

The review’s authors noted that since that several million people worldwide experience adverse heart-related events annually, even small reductions in risk can prevent hundreds of thousands of heart attacks and heart-related deaths every year.

Importantly, their analysis also found that higher omega-3 doses were more effective, and that the greatest risk reductions appeared at daily doses above 840mg of omega-3 EPA + DHA.

And the reductions in risk listed above held true even when the authors excluded the REDUCE‐IT study, which tested very high doses (4 grams daily) of omega-3 EPA in the form of a prescription fish oil. Further, when they included the results of the REDUCE‐IT trial, that further strengthened the link between daily fish oil and reduced heart-related risks.

As the paper’s lead author, Yang Hu, said, “This meta-analysis provides the most up-to-date evidence regarding the effects of omega-3 supplementation on risk of multiple CVD outcomes. We found significant protective effects of daily omega-3 supplementation against most CVD outcome risks, and the associations appeared to be in a dose-response manner.”

Surprisingly — given prior evidence that diets rich in fish (except fried fish) reduce the risk of stroke — their analysis didn’t find that supplemental fish oil reduced the risk of stroke. (See Do Fish Beat Fish Oil for Stroke?, Does Fish Fight Stroke?, and Fish May Reduce Rates of “Silent” Stroke.)

Fish oil's broad benefits warrant broad use
Professor JoAnn Manson of Harvard and Brigham and Women’s Hospital put her team’s findings in perspective.

As she said, “Although public health recommendations should focus on increasing fish consumption, having an overall heart-healthy diet, being physically active, and having other healthy lifestyle practices, this study suggests that omega-3 supplementation may have a role in appropriate patients.”

Given the results of her team’s review — which encompassed clinical trials that included healthy people — it seems odd to limit recommendation of omega-3 fish oil to “appropriate patients”.

And, since omega-3 fish oil exerts beneficial effects on brain, immune, and overall health, taking the 840mg of omega-3 EPA + DHA or more per day found most effective in the new review makes sense for almost anyone.

For more on the broad benefits of fish oil, see the Omega-3 Facts & Sources and Omega-3/6 Balance pages of our website.


  • Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, Deane KH, AlAbdulghafoor FK, Summerbell CD, Worthington HV, Song F, Hooper L. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2018 Nov 30;11:CD003177. doi: 10.1002/14651858.CD003177.pub4.
  • Aung T, Halsey J, Kromhout D, Gerstein HC, Marchioli R, Tavazzi L, Geleijnse JM, Rauch B, Ness A, Galan P, Chew EY, Bosch J, Collins R, Lewington S, Armitage J, Clarke R; Omega-3 Treatment Trialists’ Collaboration. Associations of Omega-3 Fatty Acid Supplement Use With Cardiovascular Disease Risks: Meta-analysis of 10 Trials Involving 77,917 Individuals. JAMA Cardiol. 2018 Mar 1;3(3):225-234. doi: 10.1001/jamacardio.2017.5205.
  • Hu Y, Hu FB, Manson JE. Marine Omega-3 Supplementation and Cardiovascular Disease: An Updated Meta-Analysis of 13 Randomized Controlled Trials Involving 127 477 Participants. J Am Heart Assoc. 2019 Oct;8(19):e013543. doi: 10.1161/JAHA.119.013543. Epub 2019 Sep 30.
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  • Wang C, Harris WS, Chung M, Lichtenstein AH, Balk EM, Kupelnick B, Jordan HS, Lau J. n‐3 Fatty acids from fish or fish‐oil supplements, but not α‐linolenic acid, benefit cardiovascular disease outcomes in primary‐ and secondary‐prevention studies: a systematic review. Am J Clin Nutr. 2006; 84:5–17.
  • Zheng J, Huang T, Yu Y, Hu X, Yang B, Li D. Fish consumption and CHD mortality: an updated meta‐analysis of seventeen cohort studies. Public Health Nutr. 2012; 15:725–737.