In 1970, two Danish researchers travelled to  Greenland to investigate a nutritional paradox: The Inuit people living in the region consumed foods very high in fat, yet reportedly had very low rates of heart attacks.

That observation flew in the face of nutrition dogma at the time, which held that eating fatty foods – like whale and seal meat and oily fish – would clog your arteries and cause heart disease.

The Inuit on Greenland, a Danish territory, had lower levels of blood cholesterol and triglycerides than people back in Denmark, the researchers reported. The reason, they hypothesised, was that the Inuit diet was rich in omega-3 fatty acids – particularly EPA and DHA, which are concentrated in fish and the animals that eat them.

These findings sparked decades of scientific and commercial interest in the role omega-3 fatty acids play in heart health, even after later studies suggested that, in fact, the Inuit had rates of heart disease similar to those found in Europe, the United States and Canada. Today, omega-3 supplements are among the most popular in the United States, surpassed only by multivitamins and Vitamin D. Among US adults 60 and older, about 22 per cent reported taking omega-3s in a 2017-2018 survey.

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 signalling 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 criticised for using mineral oil, which may increase the risk of heart disease, as the placebo, Dr Nissen said.)

“It would be hard for anybody who’s looking at that data to think that there’s anything there for fish oil supplements,” said Dr Ann Marie Navar, a preventive cardiologist at the University of Texas Southwestern Medical Center.

Other experts, including Dr Manson, are not so ready to give up on omega-3 supplementation. Though most clinical trials have shown no benefit of omega-3s on overall cardiovascular risk, she said, some have suggested they can reduce the risk of coronary heart disease, including heart attacks. A 2020 analysis of 32 trials, for example, found that those taking omega-3s were 9 percent less likely to have a coronary event, though the evidence was judged to be “low certainty.”

A CONSISTENT RISK OF A-FIB

For all of the debate about the potential health benefits of fish oil, there is general agreement that the supplements appear to increase the risk of atrial fibrillation, or A-fib. While the condition is not immediately life-threatening, it can increase the risk of stroke and heart failure over time, Dr Albert said.

In a 2021 study, Dr Albert and her colleagues combined the results from seven trials and concluded that taking omega-3s was associated with a 25 per cent greater risk of A-fib on average. The risk was even higher when people took larger doses, they found.

It’s not clear why fish oil might increase the risk of A-fib, Dr Albert said. But if someone develops the condition while taking fish oil, she recommends stopping the supplement.

SO, SHOULD YOU TAKE FISH OIL?

Some cardiologists, like Dr Navar and Dr Nissen, say the evidence is stacked against fish oil. When they see patients who are taking the supplements, they usually recommend that they stop.

Others experts, like Dr Manson and Dr Mozaffarian, think taking a fish oil supplement may be helpful for people who don’t eat much seafood. In the 2019 trial led by Dr Manson, omega-3s appeared to benefit people who consumed less than one and half servings of fish per week, but not those who ate more than that.

But it’s better to get omega-3s from fish than from fish oil, Dr Manson said. Eating fish provides protein, vitamins and minerals – and it’s a healthier choice than red and processed meats. Guidelines from the American Heart Association suggest consuming at least two, three-ounce servings per week. Best is fatty fish like salmon, mackerel, anchovies and sardines.

If you’re considering taking fish oil, keep in mind that there is little regulation of the supplement industry. Some fish oil supplements have been found to contain degraded, or rancid, fatty acids, which could be less effective or even harmful, Dr Navar said. For a higher-quality product, look for certification from a third party organization like the US Pharmacopeia or NSF, Dr Manson suggested.

High doses of omega-3 fatty acids may be recommended for people with very high blood triglycerides, which can increase the risk of inflammation of the pancreas, Dr Navar said. Omega-3s are an effective approach, though not the only one, for lowering triglycerides.

But if you’re looking to protect your heart, there are other changes to your diet and lifestyle that are proven to help. In contrast to the mixed evidence on fish oil supplements, there are clear benefits to the Mediterranean diet, DrNissen said, which includes fish several times per week and emphasises whole grains, fruits and vegetables, legumes, nuts, seeds and olive oil.

“People that expect heart health to come from some magical dietary supplement are really going down the wrong pathway,” he said. “Heart health comes from good, healthy habits.”

By Alice Callahan © The New York Times Company

The article originally appeared in The New York Times.

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