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 those studies have been mixed, leaving researchers and doctors still debating whether fish oil is beneficial for heart health. They have also revealed that taking fish oil is linked to a slightly greater risk of developing atrial fibrillation, a type of irregular heartbeat.
Here’s where the evidence for both the benefits and risks of fish oil stands today.
A boatload of studies, but unclear benefits
After reading the dispatches from Greenland, researchers began looking at people elsewhere in the world and finding, in study after study, that those who consumed fish at least once per week were less likely to die from coronary heart disease than those who rarely ate fish. In animal experiments, they found that fish oil helped keep electrical signaling 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 enthusiasm” about those findings, said Dr. Christine Albert, the chair of the department of cardiology at Cedars-Sinai Medical Center in Los Angeles. And it was natural to hope that people might be able to reap 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 in total cardiovascular events like heart attack and stroke. That was the finding of a 2018 meta-analysis combining the results of 10 omega-3 trials that included nearly 78,000 people. Similarly, researchers reported no overall heart health benefits of omega-3s in a 2018 trial of more than 15,000 adults with Type 2 diabetes followed for an average of seven years; in a 2019 trial of more than 25,000 adults 50 and older followed for an average of five years; and in a 2020 trial of a high dose of omega-3s tested in more than 13,000 people at risk of cardiovascular disease.
“One after another of these studies showed absolutely no benefits,” said Dr. Steven Nissen, a cardiologist at Cleveland Clinic, who led the 2020 trial. (One trial, published in 2018, did show a striking benefit of a high dose of the omega-3 EPA. But it has been widely criticized for using mineral oil, which may increase the risk of heart disease, as the placebo, Dr. Nissen said.)