In 1970, two Danish researchers traveled to Greenland to investigate a nutritional paradox: the Inuit who lived in the region consumed very high fat foods and yet they had very low heart attack rates. This observation contradicted the nutritional dogma of the time, according to which the consumption of fatty foods – such as whale meat, seal meat and oily fish – obstructed the arteries and provoked heart diseases.
According to researchers, the Inuit of Greenland, a Danish territory, had lower blood cholesterol and triglyceride levels than the inhabitants of Denmark. The reason, he hypothesized, was that the diet of the Inuit was rich in omega-3 fatty acidsespecially EPA and DHA, which are concentrated in fish and the animals that feed on it.
These findings sparked decades of scientific and commercial interest in the role of these fatty acids in heart health, even after later studies suggested that the Inuit actually had rates of heart disease similar to those of the Inuit. Europe, the United States and Canada. Today, omega-3 supplements are among the most popular in the US, second only to multivitamins and vitamin D. Among American adults ages 60 and older, about 22 percent reported taking omega-3s in a 2017-2018 survey.
Unlike most other supplements, fish oil has been rigorously studied, said 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 increased risk of developing atrial fibrillation, a type of irregular heartbeat.
This is the current state of the evidence on the benefits and risks of fish oil.
After reading the Greenland reports, researchers began studying 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 from coronary heart disease than those who rarely ate fish. They ate fish. In animal experiments, they found that fish oil helped keep electrical signaling in heart cells functioning properly, said Dariush Mozaffarian, a cardiologist and director of the Institute for Food as Medicine at Tufts University.
“There was a lot of excitement” about these findings, said Christine Albert, chief of the department of Cardiology at Cedars-Sinai Medical Center in Los Angeles. And it was natural to expect that people could get the same benefits by 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 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 of omega-3s in a 2018 trial of more than 15,000 adults with type 2 diabetes followed for an average of seven years; nor in a 2019 trial of more than 25,000 adults over age 50 followed for an average of five years; nor in a 2020 trial of a high-dose omega-3 tested on more than 13,000 people at risk of cardiovascular disease.
“One after another, these studies showed absolutely no benefit,” said Steven Nissen, a cardiologist at the Cleveland Clinic, who led the 2020 clinical trial. (One trial, published in 2018, did show a surprising benefit from a high dose of omega-3 EPA. But it has been widely criticized for using mineral oil, which can increase the risk of heart disease, as a placebo, Nissen said).
“It would be difficult for anyone looking at that data to think there’s anything in favor of fish oil supplements,” said Ann Marie Navar, a preventive cardiologist at the University of Texas Southwestern Medical Center.
Other experts, like Manson, are not so willing to give up omega-3 supplements. Although most clinical trials have not shown any benefit of these types of fatty acids on overall cardiovascular risk, he said, some have suggested that they may reduce the risk of coronary heart disease, including heart attacks. An analysis of 32 clinical trials conducted in 2020, for example, found that those taking omega-3s were 9 percent less likely to have a coronary event, although the evidence was considered “low certainty.”
Despite all the debate over the potential health benefits of fish oil, there is general agreement that supplements appear to increase the risk of atrial fibrillation. Although this condition is not immediately life-threatening, over time it can increase the risk of stroke and heart failure, according to Albert.
In a 2021 study, Albert and his colleagues combined the results of seven trials and concluded that omega-3 intake was associated with a 25 percent increased risk of atrial fibrillation on average. They found that the risk was even higher when higher doses were taken.
According to Albert, it is unclear why fish oil may increase the risk of atrial fibrillation. But if someone develops the disease while taking fish oil, she recommends stopping taking the supplement.
Some cardiologists, like Navar and Nissen, say the evidence is against fish oil. When they see patients taking these supplements, they often recommend that they stop taking them.
Other experts, such as Manson and Mozaffarian, believe that taking a fish oil supplement may be helpful for people who don’t eat many seafood foods. In the 2019 trial led by Manson, omega-3s appeared to benefit people who ate less than one and a half servings of fish a week, but not those who ate more.
But it’s better to get omega-3s from fish than from fish oil, Manson said. Eating fish provides proteins, vitamins and minerals, and is a healthier option than red and processed meats. American Heart Association guidelines suggest consuming at least two 85-gram servings per week. The best are fatty fish such as salmon, mackerel, anchovies and sardines.
If you’re thinking about taking fish oil, keep in mind that the supplement industry is poorly regulated. Some fish oil supplements have been found to contain degraded, or rancid, fatty acids, which could be less effective or even harmful, according to Navar. For a higher quality product, seek certification from a third-party organization such as the U.S. Pharmacopeia or the National Science Foundation (NSF), Manson suggested.
High doses of omega-3 fatty acids may be advisable for people with very high blood triglycerides, which can increase the risk of inflammation of the pancreas, Navar said. Omega-3s are an effective method, although not the only one, to reduce triglycerides.
But if heart protection is what you’re looking for, there are other dietary and lifestyle changes that have been shown to help. In contrast to the conflicting data on fish oil supplements, Nissen said the Mediterranean diet, which includes fish several times a week and emphasizes whole grains, fruits and vegetables, legumes, nuts, seeds and olive oil, has clear benefits.
“People who expect heart health to come from a magic dietary supplement are headed the wrong way,” he said. “Heart health comes from good, healthy habits.”
* Alice Callahan is a reporter for the Times, where she covers nutrition and health. She has a doctorate in nutrition from the University of California, Davis campus.
©The New York Times 2024
