High-Dose Fish Oil May Raise Odds for A-Fib in Heart Patients

By Amy Norton
HealthDay reporter

MONDAY, May 3, 2021 (HealthDay News) – Many people take fish oil to protect their hearts, but a new study suggests prescription versions may increase the risk of a common heart rhythm disorder.

At issue are prescription omega-3 fatty acids, which are naturally found in fish oil. Medicines are often prescribed to people with very high triglycerides, a type of blood fat linked to an increased risk of heart attack and stroke.

According to the American Heart Association, prescription omega-3s can lower triglycerides by 20-30% in most people.

But the drugs are also controversial, as their ultimate benefits for the heart are unclear.

Now the new study – an analysis of five past clinical trials – suggests caution is in order. Overall, patients in the trial receiving omega-3s were more than a third more likely to develop atrial fibrillation (a-fib) than those given a placebo. The doses of fish oil taken ranged from 0.84 grams to 4 grams per day.


A-fib is a common heart rhythm disorder, or arrhythmia, in which the upper chambers of the heart start to shake chaotically instead of effectively contracting.

A-fib is not immediately life threatening, but it is “not benign” either, said Dave Dixon, one of the study’s researchers and associate professor at Virginia Commonwealth University (VCU), in Richmond.

Over time, Dixon said, un-fib can lead to complications like heart failure or stroke.

According to Dixon, it’s unclear exactly how prescription omega-3s might contribute to fibromyalgia.

However, the increased risk was fairly consistent across all trials – more consistent, in fact, than the heart benefits, said co-investigator Salvatore Carbone, assistant professor at VCU.

In all five trials, there were more cases of fibromyalgia in omega-3 patients than in patients on placebo, although the difference in risk was not statistically significant in all studies.

But when the researchers pooled the results of the five trials together, there was one clear result: Omega-3 patients were 37% more likely to develop fibromyalgia than patients on placebo.

In contrast, only one trial has shown that an omega-3 product can reduce the risk of other heart disease.


In this trial, dubbed REDUCE-IT, patients using a product called Vascepa (icosapent ethyl) saw their risk of “cardiovascular events” drop by 25%. This included a heart attack, stroke, and death from cardiovascular causes.

Even in this study, however, the risk of fibromyalgia increased by 35% in omega-3 users.

Why did only one trial find benefits for the heart? Again, it’s not yet clear, Dixon said.

But, he added, Vascepa is different from the fish oil products tested in the other trials. It only contains one omega-3, called EPA, while the other products contain a combination of EPA and DHA.

And in the REDUCE-IT trial, Dixon said, higher levels of EPA in patients’ blood correlated with lower cardiovascular risks.

This suggests, he said, that focusing on the EPA could be “the way forward in the future”. But conflicting results on the benefits of omega-3s – as well as the potential risk of fibromyalgia – highlight the need for more studies, the researchers said.

The analysis was published on April 29 in the European Heart Journal – Cardiovascular Pharmacotherapy.


The results on the heart benefits of fish oil have indeed been “inconsistent,” Linda Van Horn, member of the Heart Association’s nutrition committee and professor at Northwestern University Feinberg School of Medicine, told Chicago.

And that includes low-dose, over-the-counter fish oil supplements.

“There is limited and inconsistent data regarding the benefit or risk of taking fish oil supplements,” Van Horn said.

So, the Heart Association recommends eating two servings of fish per week instead. Van Horn said oily fish, like salmon, trout, albacore tuna, and herring, are the best sources of omega-3s.

Current analysis trials tested prescription omega-3s. But Carbone said he would be wary of over-the-counter fish oil supplements as well.

“We don’t know if over-the-counter products could have the same effects,” he said.

Over-the-counter fish oil is considered a dietary supplement, so it’s not regulated by the U.S. Food and Drug Administration as a drug would, Dixon pointed out.

He and Carbone said it’s best to talk to a doctor or pharmacist before starting any fish oil product. and that people on prescription omega-3s should consult their doctor before stopping.


More information

Harvard Medical School has more information on fish oil and heart health.

SOURCES: Salvatore Carbone, PhD, assistant professor, kinesiology and health sciences, Virginia Commonwealth University, Richmond, Va .; Dave L. Dixon, PharmD, associate professor, ambulatory care, and vice president, clinical services, department of pharmacotherapy and outcome science, Virginia Commonwealth University, Richmond, Va .; Linda Van Horn, PhD, RD, Professor and Head, Division of Nutrition, Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, and Nutrition Committee Member, American Heart Association, Dallas; European Heart Journal – Cardiovascular Pharmacotherapy, April 29, 2021, online

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