Fish oil pills linked to higher heart-rhythm risk in healthy adults
The same UK Biobank study found a different pattern in people who already had heart or circulatory disease when it began: for them, regular fish oil users had a lower risk of some of the worst outcomes, not a higher one.
People with no heart or circulatory disease who regularly took fish oil supplements had a 13% higher chance of atrial fibrillation — an irregular, often fast heartbeat — and a slightly higher, borderline chance of stroke than non-users, a study of 415,737 UK Biobank members has found.
The same study, whose authors include academics at Sun Yat-sen University in China, found a different pattern in people who already had cardiovascular disease when they joined the study.
Regular fish oil users with existing disease had an 8% lower risk of a major cardiovascular event after developing atrial fibrillation, and a 9% lower risk of death after developing heart failure, than non-users in the same group.
All were UK Biobank members, a long-running volunteer health database that recruited people between 2006 and 2010; researchers followed them for a median of 11.9 years, up to March 2021, according to the study, published in BMJ Medicine in May 2024.
The findings “should not be concerning to people who regularly take fish oil supplements, but it’s also not a green light to start taking them to prevent heart and circulatory diseases,” the British Heart Foundation said in response to the research.
Instead, the charity said a “healthy, balanced diet which includes oily fish can provide you with omega-3 and all the other nutrients essential for keeping your heart healthy.”
The NHS recommends at least two portions of fish a week, including one oily portion such as salmon or sardines, around 140g when cooked, as the main source of long-chain omega-3 fats, which it says “can help to keep your heart healthy.”
The fish oil findings on atrial fibrillation and stroke come from an observational study: it can show a pattern but, in the authors’ own words, “no causal relations can be drawn.”
The authors also said information on the dose and type of supplements taken was not available, and that “residual confounding could still exist” — other differences between users and non-users that might explain part of the result.
A separate Cochrane review looked at omega-3 supplements and heart disease more broadly.
Drawing on 79 trials covering 112,059 people, it found high-certainty evidence that the supplements “had little or no meaningful effect on the risk of death from any cause.”
The same review found that omega-3 fats probably did reduce triglycerides, a type of fat in the blood.
The NHS separately warns against one widely sold type, cod liver oil, for a specific group: “Do not take cod liver oil or supplements containing vitamin A (sometimes called retinol) when you’re pregnant. Too much vitamin A can harm your baby’s development,” its pregnancy guidance says.