Is fish oil helpful or harmful to the heart?

Unlike most other supplements, fish oil has been rigorously studied, said Dr. JoAnn Manson, a professor of medicine at Harvard Medical School. But the results of these studies are conflicting, leaving researchers and doctors still debating whether fish oil is beneficial for heart health. They also revealed that taking fish oil is linked to a slightly increased risk of developing atrial fibrillation, a type of irregular heartbeat.

That's where the evidence for both the benefits and risks of fish oil lies today.

After reading cables from Greenland, researchers began looking at people in other parts of the world and found, in study after study, that those who consumed fish at least once a week were less likely to die of coronary heart disease than those those who ate fish rarely. In animal experiments, they found that fish oil helps keep electrical signals in heart cells functioning properly, said Dr. Dariush Mozaffarian, a cardiologist and director of the Food is Medicine Institute at Tufts University.

“There was a lot of excitement” about these findings, said Dr. Christine Albert, chair of the cardiology department at Cedars-Sinai Medical Center in Los Angeles. And it was natural to hope that people could get the same benefits from taking fish oil in supplement form, she added.

But most clinical trials of fish oil capsules have reported no reduction in death from heart disease or total cardiovascular events such as heart attack and stroke. This was the result of a 2018 meta-analysis that combined the results of 10 omega-3 studies that included nearly 78,000 people. Similarly, researchers reported no overall heart health benefits from omega-3s in a 2018 study of more than 15,000 adults with type 2 diabetes followed for an average of seven years; in a 2019 study of more than 25,000 adults aged 50 and older followed for an average of five years; and in a 2020 study of a high dose of omega-3 tested in more than 13,000 people at risk for cardiovascular disease.

“One after another these studies have shown absolutely no benefit,” said Dr. Steven Nissen, a cardiologist at the Cleveland Clinic, who led the 2020 study. (One study, published in 2018, showed a notable benefit of a high dose of omega-3 EPA has been widely criticized for using mineral oil, which can increase the risk of heart disease, as the placebo, said Dr. Nissen said.)

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