Fish Oil & Atrial Fibrillation

Reviewed 8/14/26 by the NatMed Clinical Team

Top Takeaways

AF risk is dose-dependent, rising sharply at doses over 1 gram daily – a risk many patients don't associate with a "heart-healthy" supplement.
Fish oil can also raise LDL in a dose-dependent way, so patients on higher doses should have both AF symptoms and LDL levels monitored.

About 8% of adults in the US use an omega-3 fatty acid or fish oil supplement. It’s often used for cardiovascular health, but many don’t realize there are some concerns linked to high doses and long-term use.

What is fish oil?

Fish oil comes from a variety of fish – including anchovy, salmon, sardine, tuna and many others. It’s a source of omega-3 fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It can be consumed in the diet and also taken as a supplement or prescription medication. 

Is fish oil beneficial for cardiovascular health?

For certain conditions, it can be. Fish oil is commonly used for hypertriglyceridemia and hypertension. Prescription fish oil products reduce triglyceride levels in patients with hypertriglyceridemia. Fish oil supplements might also reduce triglycerides, but up to 12 capsules daily might be needed to produce the same effects as prescription products. As for blood pressure, the FDA allows a qualified health claim stating that consuming EPA and DHA in combination may be beneficial for moderating blood pressure and reducing the risk of hypertension – though the FDA notes this claim is based on inconsistent, inconclusive evidence.

Does fish oil have downsides?

Yes, recent research suggests that taking fish oil for hypertriglyceridemia increases the risk of atrial fibrillation (AF). This risk is dose-dependent, with the highest risk at 4 grams daily. One large, high-quality clinical study in patients at high risk for cardiovascular disease (CVD) shows that taking a prescription fish oil product 4 grams daily for up to 5 years increases the risk for AF. And meta-analyses show fish oil supplements at doses over 1 gram daily are linked with a 25–37% increased risk of AF – in both patients with and without CVD. Lastly, it’s worth noting that while fish oil might reduce triglyceride levels, it might actually raise low-density lipoprotein (LDL) levels. LDL increases appear to be dose-dependent, so levels should be monitored in these patients.

What’s the bottom line?

While fish oil does offer benefits for both high triglycerides and high blood pressure, AF is a known risk associated with high doses and long-term use. Patients with existing CVD or CVD risk factors should be monitored, with a close eye on LDL levels. Fish oil use should be discontinued if AF occurs.