Unlike most other supplements, fish oil has been rigorously studied, said Dr. JoAnn Manson, a professor of medicine at Harvard Medical School. However, the results of these studies have been mixed, leaving researchers and doctors still debating whether fish oil is beneficial for heart health. They also found that taking fish oil was associated with a slightly higher risk of developing atrial fibrillation, a type of irregular heartbeat.
This is where the evidence for both the benefits and risks of fish oil lies today.
Lots of studies, but unclear benefits
After reading the Greenland dispatches, researchers began examining people in other parts of the world and found, in study after study, that those who ate fish at least once a week were less likely to die of coronary heart disease than those who ate rare fish. In animal experiments, they found that fish oil helped keep electrical signals in heart cells working properly, said Dr. Dariush Mozaffarian, 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, chairman of the cardiology department at Cedars-Sinai Medical Center in Los Angeles. And it was only natural to hope that people could get the same benefits from taking fish oil in supplement form, he added.
However, most clinical trials of fish oil capsules have not reported a reduction in deaths from heart disease or overall cardiovascular events such as heart attack and stroke. That was the finding of a 2018 meta-analysis that combined the results of 10 omega-3 trials involving nearly 78,000 people. Similarly, researchers reported no overall heart health benefits from omega-3s in a 2018 trial of more than 15,000 adults with type 2 diabetes who were followed for an average of seven years. in a 2019 trial of more than 25,000 adults 50 and older who were followed for an average of five years; and in a 2020 trial of a high-dose omega-3 tested in more than 13,000 people at risk of heart disease.
“One after another of these studies showed no benefit at all,” said Dr. Steven Nissen, a cardiologist at the Cleveland Clinic who led the 2020 trial. (One trial, published in 2018, showed a striking benefit (from a high dose of omega-3. But it has been widely criticized for using mineral oils, which can increase the risk of heart disease, as the placebo, Dr. Nissen said.)
