Could High Dose Fish Oil Increase Chances of AFib?


By Amy Norton HealthDay Reporter

Many people take fish oil to protect their hearts, but a new study suggests that prescription versions may increase the risk of common heart rhythm problems.

It’s all about prescription omega-3 fatty acids that are naturally found in fish oil. The drugs are often prescribed to people with very high levels of triglycerides, a type of blood fat that has been linked to an increased risk of heart attack and stroke.

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

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

Now, the new study – an analysis of five previous clinical trials – suggests caution is warranted. Overall, study patients given omega-3 fatty acids were more than a third more likely to develop atrial fibrillation (a-fib) than those given placebo. The doses of fish oil consumed were between 0.84 g and 4 g per day.

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

A-fib isn’t immediately life-threatening, but it’s also “not benign,” said Dave Dixon, a researcher on the study and an associate professor at Virginia Commonwealth University (VCU) in Richmond.

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

How exactly prescription-strength omega-3s could contribute to a-fib is unclear, according to Dixon.

However, the increased risk was pretty consistent across all studies – more consistent than the heart benefit, in fact, said co-researcher Salvatore Carbone, an assistant professor at VCU.

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

When the researchers pooled the results of all five studies, the result was clear: omega-3 patients were 37% more likely to develop A-fib than placebo patients.

In contrast, only one study showed that an omega-3 product could reduce the risk of other heart diseases.

In this study, known as REDUCE-IT, the risk of “cardiovascular events” in patients using a product called Vascepa (icosapent ethyl) decreased by 25%. These included heart attack, stroke, and death from cardiovascular causes.

Even in this study, the A-fib risk in omega-3 users increased by 35%.

Why has only one study found cardiac benefits? Again, it’s not clear yet, said Dixon.

However, Vascepa differs 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.

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

This suggests that focusing on EPA could be “the way forward”. However, the conflicting results on the benefits of omega-3 fatty acids – along with the potential risk of A-fib – underscore the need for further study, the researchers said.

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

Findings on the heart benefits of fish oil were indeed “inconsistent,” said Linda Van Horn, a member of the Heart Association’s nutrition committee and professor at Northwestern University’s Feinberg School of Medicine in Chicago.

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


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“There is limited and inconsistent data on the benefits or risks of taking fish oil supplements,” said Van Horn.

The Heart Association therefore recommends eating two servings of fish a week instead. Van Horn said oily fish like salmon, trout, tuna, and herring are the best sources of omega-3 fatty acids.

The studies of the current analysis tested omega-3 fatty acids with prescription strength. 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 viewed as a dietary supplement, so it’s not regulated like a drug by the U.S. Food and Drug Administration, Dixon pointed out.

Both he and Carbone said it was best to speak to a doctor or pharmacist before starting any fish oil product – and that prescription omega-3 fatty acids should speak to their doctor before weaning.

More information

Harvard Medical School is more concerned with 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 of Outpatient Care and Vice Chairman, Clinical Services, Department of Pharmacotherapy and Outcome Science, Virginia Commonwealth University, Richmond, VA; Linda Van Horn, PhD, RD, Professor and Head of Nutrition, Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, and member of the Nutritional Committee of the American Heart Association, Dallas; European Heart Journal – Cardiovascular Pharmacotherapy, April 29, 2021, online


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