Myth or fact

Fish oil capsules protect your heart

Short answerNot the way you think

By GyroscopeUpdated November 15, 20265 sources

Not the way people hope. In the VITAL trial, 25,871 US adults took 1 g of fish oil or a placebo every day for about five years, and major heart events came out about even, 386 against 419. Across seven big heart trials, fish oil capsules raised the risk of an irregular heartbeat by about 25%.

Fish oil is one of the best-selling supplements, and the idea behind it is simple. People who eat a lot of fish tend to have healthy hearts, fish is rich in the omega-3s EPA and DHA, so a capsule of those omega-3s should do the same job. The idea was reasonable enough that researchers spent years and tens of thousands of volunteers testing it, and the tests didn’t go the way it predicted.

What did VITAL find?

VITAL was one of the largest tests of fish oil in healthy people. Researchers enrolled 25,871 US adults, men 50 and older and women 55 and older, none with heart disease or cancer at the start. Half took a 1 g fish oil capsule every day, with 460 mg of EPA and 380 mg of DHA, and half took a placebo. They were followed for a median of 5.3 years.

The gap between 386 and 419 was small enough to be chance. The hazard ratio was 0.92, and its range ran from 0.80 to 1.06, which includes no effect at all. Invasive cancer was about even too, 820 against 797.

There was one bright spot. Heart attacks on their own were lower on fish oil, 145 against 200. The trial didn’t set out to test that, and when a trial looks at many outcomes, one or two can come out positive by chance. It’s a lead for future trials, and the main result, on all major heart events, stands.

What about the heartbeat?

In 2021, Gencer and colleagues pooled seven large heart trials of fish oil capsules, with 81,210 people followed for about five years. The people in these trials averaged 65 years old.

Fish oil raised the risk of atrial fibrillation, an irregular and often fast heartbeat, by about 25%. In the trials that gave more than 1 g a day, the risk was about 49% higher. In trials at 1 g a day or less, it was about 12% higher. For each extra gram a day, risk rose about 11%.

An irregular heartbeat is the last kind of side effect people expect from a product sold for the heart. The dose made a difference, which is why the tools on this site flag anything over 1 g a day.

Then why eat fish at all?

Studies of people who eat fish can’t fully separate the fish from everything else about how those people eat and live. What the capsule trials show is that the omega-3s alone, taken as a pill, didn’t prevent major heart events. Fish brings its protein along, and it takes the place of other foods on the plate. The US advice is written in ounces of fish, at least 8 ounces of seafood a week for adults, and 8 to 12 ounces from the lower mercury list in pregnancy.

What does the newest guideline say?

The 2026 US cholesterol guideline says “the use of dietary supplements is not recommended to lower LDL-C or TG”. It adds that nonprescription fish oil supplements “are not equivalent to” prescription omega-3 medicines and have variable fatty acid content. The prescription versions are used at higher doses, under a doctor, for high triglycerides. That’s a separate decision you make with your doctor, and this page doesn’t change it.

How much omega-3 is in a capsule?

Check the back of the bottle. A “1,000 mg” capsule is 1,000 mg of oil, and the EPA and DHA are listed separately on the Supplement Facts panel. In VITAL’s capsule, 840 mg of each gram was omega-3, and store capsules vary. The fish oil label check works out what yours gives you, and How many fish oil capsules a day? and Can fish oil cause an irregular heartbeat? answer the next questions.