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Is Fish Oil Linked to Heart Rhythm Changes?

How risky is fish oil or purified EPA in Vascepa when it comes to heart rhythm changes called atrial fibrillation? Learn about absolute risk!

Could a supplement that people take for heart health actually lead to heart rhythm changes? Most people take fish oil with the expectation that it will lower their likelihood of a heart attack or stroke. Articles in the medical literature have been hinting at such a benefit for more than a decade (Current Vascular Pharmacology, Jan. 2008; Cardiology Reviews, Sep-Oct. 2010). A recent study called VITAL also suggests that fish oil supplementation can reduce the risk of autoimmune diseases like rheumatoid arthritis, psoriasis, thyroid disease and polymyalgia rheumatica (BMJ, Jan. 26, 2022). You can read our take on this study here. But could omega-3 fatty acids found in fish oil trigger atrial fibrillation? Several readers have posed that question.

Does Taking Fish Oil Cause Heart Irregularities?

Q. Is there any information about fish oil causing heart irregularities? I have flares of polymyalgia rheumatica and my C-reactive protein (CRP) is high. But when I tried lowering inflammation by taking fish oil, I had irregular heartbeats. What else could I do to control inflammation?

A. In a large, randomized controlled trial called REDUCE-IT, patients taking purified fish oil (Vascepa) were more likely to experience atrial fibrillation (Journal of the American Heart Association, March 7, 2023).  People who are susceptible to this kind of irregular heart rhythm should probably avoid fish oil.

There are other ways of lowering inflammation, however. We discuss many of them in our eGuides to Alternatives for Arthritis and Cholesterol Control & Heart Health. Eating fish, as people do when following a Mediterranean-type diet, appears to help calm inflammation without increasing the risk for atrial fibrillation. Read on to learn more.

Does Fish Oil Lead to Heart Rhythm Changes?

Q. I’ve been suffering with an undiagnosed rheumatic disorder for five years. Since my eyes were affected, I started taking fish oil.

A few months later, I developed an irregular heart rhythm and read your article about the link with fish oil. I stopped the fish oil and several days later, the situation improved. Can you tell me more about fish oil and heart rhythm disturbances?

Another reader had a similar concern about heart rhythm changes:

Q. I recently learned of a 2005 Danish study that showed a correlation between atrial fibrillation and fish oil. My wife stopped taking 1.2 gm of fish oil daily and stopped fibrillating. On her doctor’s advice, she no longer has to take a drug for this problem.

Do you have any information that you can add to support a correlation between fish oil and fibrillation?

A. Your question intrigued us because research has looked at fish oil for preventing rather than causing atrial fibrillation, also known as Afib. Most of the fish oil trials have been inconclusive or shown no benefit for dangerous heart rhythm changes. However, more recent trials do suggest a connection between high doses of omega 3 fats and Afib.

Does the Dose of Fish Oil Make a Difference for Afib?

The Danish study you cited, (American Journal of Clinical Nutrition, Jan. 2005), concluded that fish consumption did not reduce the risk of atrial fibrillation. The data actually revealed a trend toward a higher risk of this rhythm abnormality among people taking more fish oil.

A later Danish study reported that people getting a moderate amount of fish oil from their diets were less likely to experience atrial fibrillation than those eating more or less fish (Europace, Nov. 2014).  The best dose provided about half as much omega-3 fat as your wife was taking.

A Randomized, Placebo-Controlled Trial and AFib:

Scientists have conducted a number of randomized placebo-controlled trials to determine whether the omega 3 fats in fish oil have cardiovascular benefits. One study with more than 8,000 people at high risk for heart attacks tested icosapent ethyl (Vascepa), a prescription drug that acts like eicosapentaenoic acid (EPA), one component of fish oil (New England Journal of Medicine, Nov. 10, 2018).  This medicine significantly reduced the chance of a heart attack or stroke. However, it also slightly increased the likelihood of atrial fibrillation (AFib).

Drilling Down to Determine Benefits and Risks:

We recently wrote about the benefits of fish oil in the VITAL trial (BMJ, Jan. 26, 2022). Here is a link to that article. It describes how this large, well-conducted study demonstrates that fish oil reduces the risk of developing several autoimmune diseases. We annoyed some readers, though.

Marie wants to know how we could praise fish oil after writing about heart rhythm changes:

“Despite your glowing endorsement of ‘gold-standard research funded by the NIH,’ for preventing autoimmune diseases, your article has done nothing but cause me confusion and concern:

“On January 10, 2022, People’s Pharmacy wrote: ‘People taking fish oil or purified EPA, a component of fish oil, appear more susceptible to heart rhythm changes called atrial fibrillation.’

“You owe your readers an explanation, please.”

Here is the straight and skinny for Marie and others who wonder how fish oil could have both pros and cons:

Let’s focus on the absolute benefits and risks of Vascepa. This is the very well-controlled trial (REDUCE-IT) of highly purified EPA from fish oil, published in the New England Journal of Medicine. The recruits had proven cardiovascular disease or diabetes and at least one additional risk factor. They were taking a statin because of their risk profile. The study lasted about five years. Over 8,000 patients were randomized to Vascepa or placebo.

Here is what the investigators were looking for:

  1. Death from cardiovascular causes
  2. Nonfatal heart attacks
  3. Nonfatal strokes
  4. Angioplasty and stent in a coronary artery
  5. Hospitalization for pre-heart attack symptoms (unstable angina)

During the five-year study, 22% of the people who received placebos experienced the above events. In the group that took Vascepa, 17.2% experienced one of those events. The absolute risk reduction was 4.8%. The number needed to treat (NNT) was 21. In other words, 21 people would need to take this purified fish oil product to protect 1 person from a very bad cardiovascular outcome such as death.

You might not think that is very good. In truth, though, it is considered quite excellent by the cardiology community. A meta-analysis of statin treatment involving over 90,000 patients produced interesting results (American Heart Journal, April, 2019).

If 1,000 people took a statin for 10 years (for primary prevention), there would have been 20 fewer heart attacks among them. No fatal heart attacks would have been prevented by statins. There would have been 7 fewer strokes out of 1,000 people treated but no fatal strokes would have been prevented. In other words, a lot of people have to take a statin to prevent one cardiovascular event. So, Vascepa looks pretty good in comparison.

Absolute Risks of Purified Fish Oil:

Let’s look at the absolute risks of purified fish oil for Marie’s benefit. Pneumonia occurred in 2.6% of the Vascepa group and in 2.9% of the placebo group. If the study was carried out over winter months, that might account for this complication. One might reasonably conclude that Vascepa did not cause pneumonia since the placebo group had a higher incidence of this lung problem.

The rate of atrial fibrillation was 5.3% in the Vascepa group compared to 3.9% in the placebo group. That was an absolute difference of 1.4%. Peripheral edema (fluid collecting in arms and legs) was 6.5% in the Vascepa cohort and 5.0% in the placebo group for a difference of 1.5%. Serious bleeding events occurred in 2.7% of the Vascepa group and 2.1% in the placebo group for a difference of 0.6%.

We draw no conclusions for Marie. We are just giving her the data to consider for herself. For some people, an incidence of atrial fibrillation of 1.4% over five years is quite worrisome. For others, that incidence would not discourage them from taking fish oil under a doctor’s supervision.

Fish Oil Helped Dry Eyes but Triggered Afib:

Q. I have had atrial fibrillation (Afib) for 15 years. Recently, I read about a study of fish oil at Cedars-Sinai. Apparently, the combination of EPA and DHA can cause Afib if the dose is over 1 gram.

I was taking an over-the-counter product for dry eyes. I stopped the product and have had no AFib in over two months.

A. Fish oil has a good reputation for treating dry eyes. However, a placebo-controlled trial does not show that relieves dry eye symptoms more than olive oil (New England Journal of Medicine, May 3, 2018).

Some doctors recommend fish oil or prescribe icosapent ethyl (Vascepa) to reduce the risk of heart attacks (EClinical Medicine, Aug. 2021). A meta-analysis of 38 studies shows that such omega-3 acids can be helpful. On the other hand, EPA (eicosapentaenoic acid) alone increases the chance of Afib by about 35 percent. It may also raise the chance of bleeding, especially if taken with anticoagulants like apixaban (Eliquis) or warfarin (Coumadin).

Readers Report Their Experiences with Fish Oil and Heart Rhythm Changes:

Pat from Bellevue, WA, reported:

“About 6 years ago I began heart irregularities, I read that there are more cases of Afib in Norway than other places and that the high amount of salmon that is consumed was associated with too much Omega 3 from salmon. After quitting both eating salmon and fish oil capsules my heart returned to normal.

“After 6 months I ate a small piece of salmon and immediately fibrillated. The problem got worse even though I quit fish of any kind. I went to a cardiologist who suggested I needed heart ablation. The operation took 7 hours and I was Afib free for a year and a half. I tried a small piece of salmon and fibrillated for 2 days before it stopped. I have been Afib-free since then and do not eat any fatty fish. Cod and shellfish are not a problem.”

Susan in Seattle, WA, also found that fish oil can trigger heart rhythm changes:

“I, too, after many years taking fish oil for dry eye, suddenly started having this problem. I discovered the new fish oil contained Vitamin E, and that causes arrhythmia in me. As soon as I stopped taking that brand of fish oil, the Afib stopped. Check the ingredient label, also the inert ingredients.”

We suggest that anyone having difficulty with unexplained Afib might consider whether they are taking fish oil supplements that might be responsible. If you have a fish oil story of your own, please share it with us below.

If you think this article is worth sharing, please scroll to the top of the page and click on the icons for email, Twitter and/or Facebook. Because Google has made our content hard to find, we count on you to help us spread to the word. Understanding absolute risks and benefit is something we think patients need to understand to better evaluate any treatment. Thank you for helping us spread the word.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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