Can fish oil cause an irregular heartbeat?
It can raise the risk. In seven large heart trials with 81,210 people, those taking fish oil capsules were about 25% more likely to develop atrial fibrillation, an irregular heartbeat, than those on placebo. In the trials that gave more than 1 g a day, the risk was about 49% higher.
Most people take fish oil for their heart, so this one surprises them. The capsules were tested in large trials to prevent heart attacks and strokes, and the researchers who pooled those trials in 2021 found the heart rhythm problem along the way. The trials didn’t test eating fish.
What we’d do: get your omega-3 from salmon, sardines or trout twice a week. If you take capsules, add up the EPA and DHA on the back of the bottle, and if a day’s total is over 1 g, talk to your doctor before you keep going. If you’ve had atrial fibrillation or palpitations, ask your doctor before taking fish oil at any dose. What foods are high in omega-3? has the fish and plants that do it without a capsule.
What the trials found
| Group of trials | People | Higher risk of atrial fibrillation |
|---|---|---|
| All seven trials | 81,210 | 25% |
| Three trials giving more than 1 g a day | 22,271 | 49% |
| Four trials giving 1 g a day or less | 58,939 | 12% |
The people in these trials averaged 65 years old and took capsules for about five years on average. Each extra gram a day of omega-3 went with about 11% more risk, so the dose counts.
Those percentages are relative. They tell you how much higher the risk was than on placebo, and in a group with a low starting risk the extra number of cases is small. They’re still big enough that we wouldn’t take high doses without a reason a doctor agrees with.
What the same capsules did for the heart
One of these trials was VITAL, in which 25,871 US adults took 1 g of fish oil a day or a placebo for a median of 5.3 years. Major heart events were 386 on fish oil and 419 on placebo, which could have been chance. Heart attacks alone were lower on fish oil, 145 against 200, but that was a secondary result, the kind a trial doesn’t set out to prove. Fish oil capsules protect your heart goes through it.
Put together, the capsules gave no clear protection against major heart events, and at higher doses a clearer sign of harm. That’s why we put fish first. The FDA’s advice for adults is at least 8 ounces of seafood a week.
When to call a doctor
If your heartbeat feels irregular, tell your doctor. If you take an omega-3 medicine your doctor prescribed, keep taking it and ask them about this, rather than stopping on your own.
3 sources
- Gencer et al., Effect of long-term marine omega-3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes, Circulation, 2021pmc.ncbi.nlm.nih.gov
- Manson et al., Marine n-3 fatty acids and prevention of cardiovascular disease and cancer (VITAL), New England Journal of Medicine, 2019pmc.ncbi.nlm.nih.gov
- US Food and Drug Administration, Advice about Eating Fish, current as of March 5, 2024fda.gov
