Fish and Cardiovascular Disease

Epidemiologists have observed a low risk of coronary heart disease mortality among native Alaskan and Greenland Eskimos and Japanese who consumed a large amount of fish (3). This led researchers to take an interest in fish and fish oil supplementation in the prevention and treatment of heart disease. At the same time, Eskimos have been found to have a high rate of hemorrhage (4), a risk factor for hemorrhagic stroke, which is also likely due to eating large amounts of fish.

In April, PCRM sent out a news release, Fish Oil Does Not Prevent Heart Disease, reporting on a meta-analysis of fish oil supplement trials. I decided to look into it more, and here is what I found.

Secondary Prevention

In April 2012, a meta-analysis of clinical trails using fish oil supplements to treat heart disease was reported in the Archives of Internal Medicine (conducted by the Korean Meta-analysis Study Group (1)). It combined data from 14 randomized, double-blinded, placebo-controlled trials and found that supplementing with fish oil did not reduce the risk of overall cardiovascular events, all-cause mortality, sudden cardiac death, myocardial infarction, congestive heart failure, transient ischemic stroke, or overall stroke in people with a history of cardiovascular disease.

The results of this study contradicted two large clinical trials with fish oil supplements, the Gruppo Italiano per lo Studio della Sopravvivenza nell’Infarto Miocardico (GISSI) and the Japan EPA Lipid Intervention Study. Both of these studies found a protective effect of fish oil supplementation, but they were not included in the meta-analysis because they did not contain a placebo group. In an accompanying editorial (2), Drs. Frank Hu and JoAnn Manson of the Harvard School of Public Health argued that due to the studies in the meta-analysis having relatively small numbers of people, the evidence from these two larger clinical trials should not have been completely ignored. But, Drs. Hu and Manson also conclude that “To date, there is no conclusive evidence to recommend fish oil supplementation for primary or secondary prevention of [cardiovascular disease].”

Primary Prevention

The above discussion is about secondary prevention, or preventing cardiovascular events in people who have already been diagnosed with cardiovascular disease. According to the Korean Meta-analysis Study Group, there have not been any primary prevention studies of fish oil supplementation in a population free of cardiovascular disease at baseline.

As distinct from fish oil supplementation, there have been two meta-analyses on fish consumption and primary prevention of heart disease (3) and stroke (4). Both were conducted by the Northwestern University Feinberg School of Medicine.

The meta-analysis on fish intake and heart disease combined data from 13 cohort groups and found that eating fish once per week could significantly reduce death from coronary heart disease by 15% in comparison to eating fish less than once per month. The trend for non-fatal heart attacks was not strong nor statistically significant.

The meta-analysis on fish and stroke combined data from nine cohort groups and found that eating fish one to three times per month was protective against ischemic stroke (in which a blood clot prevents the brain from receiving blood), which makes up 87% of strokes. Fish intake was not protective against hemorrhagic stroke (in which bleeding in the brain causes pressure on the brain tissue). See the American Stroke Association’s website for some interesting illustrations of the different types of stroke.

Conclusion

Based on the available evidence, moderate amounts of fish appear to be protective against heart disease and ischemic stroke, but fish oil supplementation probably does not prevent heart disease events or death in people already diagnosed with heart disease.

I am not suggesting people eat fish and it’s worth noting that a vegetarian diet has been associated with a 24% lower risk of heart disease mortality (link). I recommend that most vegans take a DHA supplement to make sure they are on par with fish eaters (link).

References

1. Kwak SM, Myung SK, Lee YJ, Seo HG; for the Korean Meta-analysis Study Group. Efficacy of Omega-3 Fatty Acid Supplements (Eicosapentaenoic Acid and Docosahexaenoic Acid) in the Secondary Prevention of Cardiovascular Disease: A Meta-analysis of Randomized, Double-blind, Placebo-Controlled Trials. Arch Intern Med. 2012 Apr 9. [Epub ahead of print] | link

2. Hu FB, Manson JE. Omega-3 Fatty Acids and Secondary Prevention of Cardiovascular Disease–Is It Just a Fish Tale?: Comment on “Efficacy of Omega-3 Fatty Acid Supplements (Eicosapentaenoic Acid and Docosahexaenoic Acid) in the Secondary Prevention of Cardiovascular Disease”. Arch Intern Med. 2012 Apr 9.
[Epub ahead of print] | link

3. He K, Song Y, Daviglus ML, Liu K, Van Horn L, Dyer AR, Greenland P. Accumulated evidence on fish consumption and coronary heart disease mortality: a meta-analysis of cohort studies. Circulation. 2004 Jun 8;109(22):2705-11. | link

4. He K, Song Y, Daviglus ML, Liu K, Van Horn L, Dyer AR, Goldbourt U, Greenland P. Fish consumption and incidence of stroke: a meta-analysis of cohort studies. Stroke. 2004 Jul;35(7):1538-42. Epub 2004 May 20. | link

8 Responses to “Fish and Cardiovascular Disease”

  1. Miles Southan Says:

    I wonder if it could be the high taurine content of fish that causes dietary fish intake to correlate with improved cardiovascular health more consistently than fish oil. Taurine is a powerful modulator of blood sugar. It also lowers cholesterol and prevents oxidative stress.

    Fortunately, if we want to, we can take synthetic taurine supplements. Apparently certain algae like nori contain some small amount of taurine as well. http://www.springerlink.com/content/h15t30048j0r0447/

    And in fact, some people have tried to demonstrate that a vegan diet paired with a taurine supplement is a potent combination for heart health and reducing in AGEs which are linked to an assortment of health problems.
    http://www.ncbi.nlm.nih.gov/pubmed/15288360
    http://www.ncbi.nlm.nih.gov/pubmed/15607576

  2. Reijo Laatikainen Says:

    I agree with you Jack. The benefits of omega-3 supplementation might be smaller than GISSi and JELIS studies suggested. One additional important piece of information in the Kwak et al. study, there seemed to be no additional benefit of omega-3 FAs on top of statins. This is in line with another meta-analysis by Chen et al. 2011, who concluded: “..In patients with guidelines-adjusted therapy, omega-3 fatty acids did not reduce the risk ratio (RR) of sudden cardiac death…”

    I don’t either say, omega-3 FAs would be nonesense, but all the hype is just not justified.

    Miles, thanks for interesting links.

  3. Cobie deLespinasse Says:

    You folks at Vegan Outreach have some good general info about fish under “Widening the Circle of Compassion”:

    http://www.veganoutreach.org/whyvegan/widening.html

  4. Marla Clark Says:

    What about flaxseed oil? It has omega 3, 6 and 9’s? Good plant based supplement with high lignans. I have reason to believe that eating fish, shrimp and other sea creatures farmed in Asian countries are fed “tankage” that comes from rendering plants in California, from which euthanized pets, dogs and cats, wind up in this mess fed to farmed sea creatures. Then this seafood is shipped back to the US and sold in supermarkets. Oh by the way, it’s perfectly legal. YUCK! (For reference read “Food Pets Die For” by Ann Martin.) Be careful what you eat and feed to your pet. Good reason to be vegan.

  5. Jack Norris RD Says:

    > What about flaxseed oil?

    There has been less research on ALA, the form of omega-3 in flaxseed oil. My recommendations for ALA are here under Omega-3s:

    http://veganhealth.org/articles/dailyrecs

  6. S Meyers Says:

    Television from French Swiss (TSR) recently did an expose on how chickens are raised throughout the EU. The interest is that the regulations in Switzerland for raising chicken is much more strict (and “compassionate”-if you think that raising animals for food can be compassionate) than elsewhere in Europe and has been for over 20 years. The TSR showed images that would be banned on US TV-images taken by PETA! Evidently, when the Swiss first saw these images, and were educated about the abusive practices, they immediately passed a law outlawing the typical commercial chicken raising practices. The issue now is that they import up to 50% of the chicken from other EU nations and they do not adhere to Switzerland’s laws. The expose will continue next week . . . you can catch it on TSR.ch or do a search.

  7. Amanda Says:

    Is fortified food okay, now that vegan foods are being fortified with “Life’s DHA”? I drink DHA soy milk every day and regularly eat spaghetti sauce that contains it, but from what I can tell there is nothing on the labels to indicate how much of the necessary Omega 3s you are getting…

  8. Jack Norris RD Says:

    There’s probably not enough DHA in fortified foods to cause any problems.

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