Does fish oil cause heart problems?

One signal, and the two numbers it deserves, relative and absolute

Does fish oil cause heart problems is a question the careful-claims flag answers with one signal rather than a reassurance or an alarm, and the signal deserves both of the numbers that describe a risk, because the relative number is what makes headlines and the absolute number is what a reader needs. The signal: meta-analyses of the large cardiovascular outcome trials of marine omega-3, the trials that gave a gram a day and, in one, four grams of purified EPA, to tens of thousands of adults for years, find a rise in the risk of atrial fibrillation, the irregular heart rhythm, in those given omega-3 against placebo. The relative number: around a quarter more atrial fibrillation across the trials pooled, and around a half more at four grams a day, the relationship being dose-related, present at around two grams and small or absent at doses below a gram, the atrial fibrillation literature's finding and the honest ceiling every high-dose page here names. The absolute number: the underlying risk of atrial fibrillation in the trials' populations, older adults with cardiovascular risk followed for five to seven years, was a few percent, so a relative rise of a quarter to a half added a fraction of one percent of participants as new cases, a real harm in a large population and a small one for an individual, and one that is dose-related enough that a healthy adult on a standard softgel is not in the population or at the dose where it was found. A reader who sees only the relative number fears a standard softgel; a reader who sees only the absolute number dismisses four grams; both numbers together put the signal where it belongs, at the high rungs, in a cardiologist's hands.

The other side of the ledger, the heart claim and the outcome trials, who the signal is for, and the question filed

The other side of the ledger is what fish oil does for the heart, and it is more modest than the shelf says and more honest than the fear. The register's claim: EPA and DHA contribute to the maintenance of normal heart function at 250mg a day, a maintenance sentence describing what adequate intake supports, reached by one standard softgel or two fish portions a week, and not a prevention claim. The outcome trials: at around a gram a day in primary prevention, no meaningful reduction in heart attacks, strokes or cardiovascular deaths, the supplement-dose story being maintenance rather than protection, and at four grams of purified prescription EPA in patients with raised triglycerides on statins, a reduction in events in one large trial alongside the clearest atrial fibrillation signal, a treatment dose in a high-risk population whose balance of benefit and harm a cardiologist weighs for each patient, the outcome-trial literature's split. So fish oil at a standard dose neither prevents heart problems nor causes them, maintaining normal function below the signal, and fish oil at four grams both reduces events and raises atrial fibrillation in the people it was tested in, a trade that belongs to a prescriber. Who the signal is for, then: a reader with a history of atrial fibrillation or at high cardiovascular risk, who stays on the standard rung without a cardiologist's say; a reader considering the two- and three-gram claim doses or the four-gram research dose, who has a triglyceride or blood pressure reason and a GP who knows; and nobody on a standard softgel, whose 300mg sits below the dose at which the signal was found. A reader who notices palpitations, a racing or irregular heartbeat, on any dose sees a GP, the symptom having many causes and a simple test, and mentions the fish oil. The question filed: one signal, atrial fibrillation, a relative rise of a quarter to a half against a small absolute risk, dose-related and small or absent below a gram, set beside a maintenance claim at 250mg and no prevention at a gram, with a standard softgel below the signal and the high rungs a cardiologist's, and the worked example being that standard softgel, one at 17p, £14.99 for 90.

The verdict, a real signal at high doses, in both numbers, and a standard softgel beneath it

Does fish oil cause heart problems: one signal, atrial fibrillation, which the cardiovascular outcome trials find raised by around a quarter overall and around a half at four grams a day in relative terms, against an underlying risk of a few percent over years so that the added cases were a fraction of one percent of participants in absolute terms, dose-related and small or absent below a gram, set beside the register's maintenance claim at 250mg and the outcome trials' finding of no prevention at a gram and a benefit-and-harm trade at four grams of prescription EPA that a cardiologist weighs, so that a standard softgel sits below the signal, the high rungs belong to a reader with a reason and a doctor, and palpitations on any dose go to a GP. A standard softgel below the signal: Futuro Labs Omega 3 Fish Oil, one softgel with food, 180mg EPA and 120mg DHA, 90 for £14.99 at 17p a day.

What to check on the label

Questions people also ask

Can fish oil cause atrial fibrillation?

At high doses, the outcome trials find a signal: a relative rise of around a quarter across the trials and around a half at four grams a day, dose-related and small or absent below a gram, against an underlying risk of a few percent over years so that the added cases were a fraction of one percent, a real harm at the high rungs and not at a standard softgel.

Is fish oil good or bad for the heart?

Both answers are modest: the register's claim at 250mg is the maintenance of normal heart function, the outcome trials found no prevention of heart attacks and strokes at a gram a day, and four grams of prescription EPA reduced events in high-risk patients alongside the clearest atrial fibrillation signal, a trade a cardiologist weighs.

Should I stop fish oil if I have a heart condition?

Not without asking: a reader with a history of atrial fibrillation or at high cardiovascular risk stays on the standard rung, a 250mg softgel below the dose at which the signal was found, and discusses any higher dose with a cardiologist, mentioning the fish oil at every review.

What is the absolute risk of atrial fibrillation from fish oil?

Small: in trials where a few percent of older adults with cardiovascular risk developed atrial fibrillation over five to seven years, omega-3 added a fraction of one percent of participants as new cases, mostly at two to four grams a day, the relative rise of a quarter to a half being the headline and the absolute rise the reality.

What should I do if I get palpitations on fish oil?

See a GP: a racing or irregular heartbeat has many causes, caffeine, stress, thyroid and rhythm problems among them, and a simple test sorts them, with the fish oil mentioned and paused on advice, especially if the dose was at the high rungs.

Sources

1. Meta-analyses of cardiovascular outcome trials of marine omega-3: a dose-related increase in the risk of atrial fibrillation, most evident at doses of four grams a day and small or absent below one gram, a finding that sets the honest ceiling of high-dose omega-3 for a healthy adult. PubMed record
2. The large cardiovascular outcome trials of omega-3: around a gram a day of EPA and DHA in primary-prevention populations produced no meaningful reduction in major cardiovascular events, while four grams of purified EPA in people with raised triglycerides on statins reduced events in one large trial, so the supplement-dose story is maintenance and the treatment-dose story is a prescription. PubMed record
3. EFSA Panel on Dietetic Products. Scientific opinion on the substantiation of health claims related to EPA and DHA and normal function of the heart (250mg daily condition of use). EFSA Journal 2010;8(10):1796. https://www.efsa.europa.eu/en/efsajournal/pub/1796
4. Electronic medicines compendium (emc): Summaries of Product Characteristics for omega-3-acid ethyl esters 1000mg capsules (Omacor and generics) and icosapent ethyl (Vazkepa). https://www.medicines.org.uk/emc/search?q=omega-3-acid+ethyl+esters

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