Why Fish Oil Supplements Can Be Dangerous for Your Heart

MMost people are familiar with the best things to eat for a healthy heart: vegetables, low-fat dairy products and lean proteins like fish. Some fish, like salmon, also have the added benefit of being rich in omega-3 fatty acids, which are healthy fats that can help raise good cholesterol and lower triglycerides.

Or so we think. Studies on the benefits of fish oil and fish oil supplements have not been as conclusive when it comes to actually preventing heart disease in people who are not at higher risk. In the most recent, published in BMJresearchers report that people with no history of heart problems who regularly took fish oil supplements had an increased risk of atrial fibrillation.

The study involved more than 415,000 men and women from the UK Biobank health data center who agreed to share their health records and answer questions about their diets and supplement consumption. Participants joined between 2006 and 2010 and were followed until 2021 or until they died, with most people followed for an average of almost 12 years. Overall, about a third of them used fish oil supplements.

Among people without a history of heart disease, those who regularly took fish oil supplements had a 13% higher risk of developing atrial fibrillation and a 5% higher risk of stroke compared to those who did not take the supplements. The researchers also divided the participants by the severity of the heart-related outcomes they experienced: Women who started out without heart problems had a 6% greater chance of having a heart attack, stroke, or heart failure if they took fish oil supplements compared to for those who didn’t take them.

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For people who already had a history of heart disease, however, the results were very different. For them, as previous studies have shown, regular fish oil supplementation was associated with a 15% lower risk of progressing to more serious heart problems – from having atrial fibrillation to having a heart attack, for example, or worsening heart failure. until death. .

Alice Lichtenstein, director and senior scientist at the Cardiovascular Nutrition Laboratory at Tufts University and an expert volunteer with the American Heart Association (who was not involved in the study), says the risk of atrial fibrillation associated with fish oil supplementation — especially at high levels doses – is not new. And the risk observed in this study may reflect the fact that some people were taking higher doses, since the researchers only asked people to report their use of supplements and could not verify either their actual use or the doses they took. . “The only answer option for regular use of fish oil supplements [in the study] it was ‘yes’ or ‘no,’ and supplement use is rarely so consistent,” says Lichtenstein. “The authors [also] We do not have information about the type of fish oil supplement consumed, which can vary greatly, and the dose taken.”

The design of the study may also explain some of the differences in results between people who had no history of heart problems and those who did. Because the study was conducted as an observational analysis rather than a randomized clinical trial in which people were given specific doses of fish oil supplements and closely monitored, the researchers were unable to control or adjust for a number of different factors in the study population. , including the reasons people took fish oil and their underlying health at the start of the trial.

At the largest randomized clinical trial of fish oil in a healthy population without known heart problems, reported in 2018, fish oil supplements were associated with a 28% lower risk of heart attacks and an overall 17% reduction in the risk of all disease events cardiac. In this study, however, supplements were not associated with a lower risk of stroke. JoAnn Manson, chief of the division of preventive medicine at Harvard Medical School and a physician at Brigham and Women’s Hospital who co-led the study, says these results are probably more indicative of how fish oil affects the heart, since the study used quality-controlled supplement sources and carefully monitored participants’ dosages.

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“The bottom line is that I believe randomized trials show differences in the risk of atrial fibrillation that are dose dependent,” she says. “Doses of 1g per day and lower are not associated with a significant increase in atrial fibrillation. But doses greater than 1g per day show a substantial risk, close to 50%, of atrial fibrillation.”

The reason for the risk may be related to the physiological effects of fish oil. The omega-3 fatty acids in fish oil can affect the electrical rhythms of the heart, in particular the beating of the upper or atrial chambers.

It is because of this risk that the American Heart Association does not Not recommended Fish oil supplements to prevent heart disease. “Fish oil supplements are not routinely recommended for the prevention or treatment of heart disease, especially considering the potential increased risk of developing atrial fibrillation,” says Lichtenstein. Instead, she says, people interested in protecting themselves from heart problems should follow a healthy diet that includes eating fish about one to two times a week, exercising regularly, minimizing stress and getting enough sleep.

But For people more likely to have heart problems, the risk of atrial fibrillation is balanced by the potential anti-inflammatory, anticoagulant, and triglyceride-lowering benefits of omega-3 fats, which tend to protect the heart and lower the risk of coronary events. As the study shows, people who already have a history of heart disease and who don’t eat a lot of fish regularly tend to benefit more from these effects; this protection does not appear to transfer to people hoping to reduce their risk of a first cardiac event.

“Correlation does not prove causation,” Manson says of the study results. “I don’t think the public should be alarmed by this study because most organizations currently do not recommend omega-3 supplements for primary prevention of heart disease. Currently, they recommend one to two servings of fish per week.”