More threads by David Baxter PhD

David Baxter PhD

Late Founder
Fish Oil Supplements May Be Harmful To Patients With Abnormal Heart Rhythms
June 14th, 2005

While Omega-3 supplements are generally considered safe they may adversely affect patients with abnormal heart rhythms.

Oregon Heart Researchers Find Fish Oil Supplements May Be Harmful To Patients With Abnormal Heart Rhythms
Fish oil may be good for some heart conditions, but not dangerous heart rhythms

Portland, Ore. - Fish oil supplements have proved effective in reducing the risk of sudden cardiac death, but a new study shows the oil may actually increase life-threatening abnormal heart rhythms in patients with implanted defibrillators.

The study, led by heart researchers at the Portland Veterans Affairs Medical Center and Oregon Health & Science University will be published in the June 15 issue of The Journal of the American Medical Association.

"We were very surprised by the study results. Previous studies have suggested that fish oil might actually prevent life-threatening abnormal heart rhythms," said Merritt Raitt, M.D., physician at the Portland Veterans Affairs Medical Center and associate professor of medicine (cardiology) in the Oregon Health & Science University School of Medicine. "But our results indicate that this supplement might actually be harmful and increase the risk of life-threatening heart rhythms in this group of patients."

Researchers enrolled patients who had suffered from recent episodes of either ventricular tachycardia (VT) or ventricular fibrillation (VF), dangerous rapid heart rhythms that originate in the ventricles of the heart, the main pumping chambers, and can lead to cardiac arrest and sudden death. The study specifically looked at 200 patients from six medical centers between February 1999 to January 2003. All the patients had implantable cardioverter defibrillators (ICD) that protected them against these life-threatening abnormal heart rhythms by automatically detecting and treating VT and VF with pacing and/or shocks.

In this randomized, double-blind trial, half the patients received a placebo, in this case olive oil, while the other half received 1.8 g of fish oil, omega-3 polyunsaturated fatty acids. The patients who received the fish oil supplements had blood levels of omega-3 polyunsaturated fatty acids that in previous studies were associated with a reduced risk of sudden death.

Every three months during a two-year period, the ICD memories were reviewed for episodes of VT and VF. Researchers then compared the number of episodes in the placebo group with that of the fish oil group.

The results showed fish oil did not prevent life-threatening abnormal heart rhythms, rather, it tended to increase the risk of VT and VF. After 6 months in the study, 36 percent of patients assigned to the placebo had an episode of VT or VF compared with 46 percent of patients who were in the fish oil group.

The effect was most prominent in the subset of 133 patients, who had suffered from VT at the time they entered the study. Researchers found that by 6 months, 37 percent of these patients assigned to placebo had experienced an episode of VT or VF compared with 61 percent of patients in the fish oil group. Over the entire course of the study recurrent episodes of VT or VF were significantly more likely to occur in the patients assigned to fish oil.

"We still believe that fish oil supplements or dietary fish intake can be beneficial by reducing sudden death in patients with a recent heart attack, as large studies have shown. However, it appears that this benefit is either not due to a reduction in abnormal heart rhythms or perhaps fish oil may have different effects on life-threatening heart rhythms in different situations," said Raitt. "Based on this research, we recommend that patients who have had life-threatening abnormal heart rhythms and implanted defibrillators should avoid fish oil supplements."


Fish oil is an important source of Omega-3 Fatty Acids. As we have reported in the past, these seem to have positive effects on anxiety and depression disorders

Study links brain fatty acid levels to depression

Abstract: Dietary Omega-3 Fatty Acids and Psychiatry

Antidepressant foods

While this study indicates that fish oil may be contraindicated for some heart disease patients this should not deter healthy anxiety or depression sufferers from taking it. If in doubt consult your doctor.

An alternative Omega-3 source is Flax seed (Linseed). Because Linseed oil has a short shelf-life eating the seed may be preferable to buying the oil. Seeds must be dehulled or crushed as the red skin prevents the seed from being digested. Linseed has mild laxative properties which may alleviate the constipation produced by some antidepressants.


Hi Doc,
:? Is taking omega-3 still safe if no abnormal heart rhythms :?
Just curious, other than any expected side effects!
Do you know about Primrose Oil :?
Thanks Holly

David Baxter PhD

Late Founder
As far as I know, yes. In the vast majority of people, increasing omega-3 intake is a good thing. The most common side-effect with supplements is likely to be tummy troubles and that's not serious, just a bit uncomfortable.

I don't know of anything negative about Primrose Oil, other than that it's a bad substitute for 5W30 in Canadian winters.

David Baxter PhD

Late Founder
No. I said DON'T use Primrose Oil instead of 5W30 - you'll freeze up and then you'll need to thaw out and get a jump start or you'll pop all your frost plugs :panic:


Hi Doc,
Been there, done that already, not really any difference! :p
Too old for plugs it is a computer chip today! :shocked: :eek:
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