Fish oil supplements may not always benefit everyone. Recent studies revealed a complex picture: while some research suggests that omega-3 fatty acids in fish oil can reduce triglycerides and potentially improve heart health, other studies show that high doses of fish oil are associated with a higher risk of atrial fibrillation (AFib). People with AFib have an increased risk for other cardiovascular conditions, such as stroke, blood clots, and heart failure.

A new study published in BMJ Medicine found that fish oil supplements were associated with a 13% increased risk of AFib and a 5% higher chance of stroke for people without pre-existing heart disease.

“The general consensus has been that taking OTC fish oils is not harmful and may be beneficial. However, with the recent study published in the BMJ, this may not be the case,” Monica Sanchez Shields, MD, a cardiovascular specialist at UTHealth Houston who was not involved in the study, told Verywell in an email.

The Complicated Relationship Between Fish Oil and Heart Health

The risks associated with fish oil supplements may not apply to patients who already have heart conditions. For patients with heart failure, fish oil supplements can reduce inflammation and improve heart function.

The BMJ Medicine study showed that for participants with heart disease, fish oil supplements were associated with a reduced risk of the disease progressing to heart attack or death.

“This may be due to the anticoagulant and/or anti-inflammatory effects of fish oils,” Sanchez Shields said. “Overall, it seems more research needs to be done in this area to fully understand these results.”

Evidence on the connection between fish oil supplements and AFib risk has also been mixed. While one 2021 trial found that fish oil had no impact on AFib risk, a meta-analysis published the same year suggested that one gram or more of omega-3 fatty acids per day led to a 49% increased risk of AFib.

A typical fish oil supplement contains about 1,000 mg of fish oil, with 180 mg of eicosapentaenoic acid (EPA) and 120 mg of docosahexaenoic acid (DHA)—the two major types of omega-3s. However, the formulations and dosages can vary widely from brand to brand.

While there’s no official safety limit for omega-3 consumption, the Food and Drug Administration (FDA) said that dietary supplements providing no more than 5 grams of EPA and DHA per day are safe when used as recommended or suggested in their labeling.

In a study conducted by the American Heart Association, a daily dose of 4 grams of combined EPA and DHA are effective at treating very high triglycerides.

“Prescription fish oils are very effective in reducing high triglyceride levels and are used frequently in this subset of patients,” Sanchez Shields said.

How to Decide Whether Fish Oil Is Right for You

The USDA recommends that most adults eat at least 8 ounces of seafood each week to get omega-3 fatty acids.

“If your intake is less, then a fish oil supplement may be helpful,” said Lena Beal, MS, RDN, LD, a cardiovascular dietitian at Piedmont Atlanta Hospital.

Supplements help certain people meet their daily omega-3 requirements, avoid deficiencies, or manage health conditions. However, fatty fish like salmon, sardines, and herring are better for heart health than just using supplements, Beal added.

While there’s no evidence that fish oil supplements reduce the risk of heart disease, people who consume seafood one to four times per week have a lower chance of dying from heart disease.

Most experts recommend prioritizing omega-3s from dietary sources like oily fish instead of supplements because whole foods contain additional beneficial nutrients.

“The BMJ study may serve as a reminder that eating a healthy diet is more effective for heart health than taking OTC supplements,” Sanchez Shields said.