Research Finds Link Between Fish Oil Supplements and Higher Risk of Stroke, AFib in Certain Individuals

As a source of omega-3 fatty acids, fish oil supplements have become popular for people seeking to boost heart health. But recent research suggests that, for some people, the supplements may instead raise the risk of adverse cardiovascular outcomes. 

For the study, published in the journal BMJ Medicine, researchers turned to a large biomedical database and resource called the UK Biobank. They analyzed the data of more than 415,000 people between the ages of 40 and 69, nearly a third of whom indicated that they regularly supplement with fish oil.

What they discovered is that people with good cardiovascular health who regularly took fish oil had a 5% higher risk of stroke and a 13% increased risk of atrial fibrillation (or AFib), which causes a rapid and often irregular heartbeat and raises the risk of stroke and heart attack over time.

On the flip side, people with heart issues who routinely took fish oil supplements had a 15% lower risk of AFib progressing to a heart attack and 9% reduced odds of heart disease leading to death. 

“This study highlights the nuanced relationship between fish oil supplements and heart health, emphasizing that universal recommendations on supplements can be potentially dangerous,” Michelle Routhenstein, RD, a preventive cardiology dietitian and registered dietitian nutritionist, told Health. “It also emphasizes the importance of individualized recommendations based on factors like medical history.”

Here’s what you need to know about the potential risks of taking fish oil supplements, who might benefit from them, and what experts say to consider before trying them.

Interest in the connection between omega-3 fatty acids and heart health took off in the 1970s, when scientists hypothesized that Greenland’s Inuit people had better heart health because they ate so much fatty fish.

These days, about 19 million people in the United States take fish oil in supplement form—many to treat or prevent heart disease. However, many clinical trials investigating the effects of fish oil supplements on cardiovascular outcomes have shown no clear advantages. 

For instance, a study of more than 15,000 people with diabetes found that people taking a fish oil supplement did not have a reduced risk of having a serious cardiovascular event compared to people who didn’t take supplements. In another study, researchers discovered that taking fish oil did nothing to reduce the risk of heart attack, stroke, or cancer.

“Prior randomized clinical trials have not shown a cardiovascular benefit,” Deepak L. Bhatt, MD, the director of Mount Sinai Fuster Heart Hospital at the Icahn School of Medicine at Mount Sinai, told Health. “And this [current] observational study suggests that there may additionally be a risk of atrial fibrillation.”

This study isn’t the first to link the use of fish oil supplements with a heightened AFib risk. Research from 2021 that analyzed seven studies found an association between the two, especially when fish oil was taken at higher doses. 

“These supplements at high doses are thought to affect certain chemical pathways in the heart, which can affect how electricity flows through the heart,” Majid Basit, MD, a cardiologist with Memorial Hermann Health System in Texas, told Health. “This may put people at risk for certain types of arrhythmias like atrial fibrillation.”

Basit said, however, that further research is needed to understand how fish oil supplements may negatively affect the heart.

Experts say some people may benefit from fish oil supplementation, however. 

For example, fish oil supplements could be helpful for people who don’t get enough omega-3 fatty acids in their diet, 'provided it's at an appropriate dose' and 'sourced from a high-quality supplement,' Routhenstein said.

Basit pointed out, however, that fish oil supplements should never be used as a substitute for a healthy diet that includes fruits, vegetables, grains, and oily fish.

Fish oil could also be helpful for people with elevated triglyceride levels, according to Routhenstein. “Certain doses of omega-3 fatty acids present in fish oil have shown promise in promoting heart health by potentially reducing triglyceride levels,” he said.

However, a better option for people with elevated triglycerides, provided they have also had an adverse event such as a prior heart attack, might be the prescription medicine known as icosapent ethyl, Bhatt said. “It is a purified form of the omega-3 fatty acid eicosapentaenoic acid (EPA) that has been shown to reduce the risk of heart attack, stroke, and death from cardiovascular causes, and in appropriate patients has been approved by the FDA.”

Experts agree that people should speak to a healthcare provider before taking fish oil supplements.