Fish oil supplements may raise risk of stroke, heart issues, study suggests

(CNN) — As an excellent source of heart-healthy omega-3 fatty acids, daily fish oil supplements are a popular way to keep the risk of cardiovascular disease at bay.

About 20% of adults older than age 60 in the United States frequently use these products with the aim of supporting heart health.

However, a new study finds regular use of fish oil supplements may increase, not reduce, the risk of first-time stroke and atrial fibrillation among people in good cardiovascular health.

Atrial fibrillation, also called AFib or AF, is a type of arrhythmia, or irregular heartbeat, that people often describe as a flutter or pounding in their chests.

“I can see the headline for this study as ‘Fish oil supplements: Is it time to dump them or not?’” said cardiologist Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver.

“I say that because over-the-counter fish oil is very seldom recommended, is in none of the guidelines from professional medical societies, and yet that’s what most people take,” said Freeman, who was not involved in the study.

Fish oil only helped people with existing heart disease

The study analyzed data on over 415,000 people ages 40 to 69 participating in the UK Biobank, a longitudinal study of the health of people in the United Kingdom. Nearly one-third of those people, who were followed for an average of 12 years, said they regularly used fish oil supplements.

For people without heart issues, regular use of fish oil supplements was associated with a 13% higher risk of developing atrial fibrillation and a 5% heightened risk of having a stroke, according to the study, published Tuesday in the journal BMJ Medicine.

Over-the-counter fish oil suffers from a lack of purity and consistency, as well as the potential contaminants and heavy metals such as mercury that come with fish, Freeman said.

“In addition, studies over the last 10 years have not been very positive for over-the-counter fish oil,” he added. “Fish oil was either having no benefit or in some cases it may harm, such as with stroke and AFib. So that’s not new.”

In fact, the new study found that people with existing heart disease at the beginning of the research had a 15% lower risk of progressing from atrial fibrillation to a heart attack and a 9% lower risk of progressing from heart failure to death when they regularly used fish oil.

Instead, prescription versions of fish oil, such as Vascepa and Lovaza, are used to counter such risk factors such as high triglycerides, a type of blood fat, in people with cardiovascular disease risk, Freeman said.

“But even in the prescription strength, highly purified versions of fish oil, the risk for AFib and sometimes stroke has also been present and doctors are cautious about that,” Freeman said.

“Overall, I would say that the days where people just go to the store and buy buckets of fish oil pills to keep them well should be over, but fish oil may still have a role in people who are already sick.”

Try to use food sources for omega-3s

When it comes to fish oil, “the devil is in the details,” said Alzheimer’s preventive neurologist Dr. Richard Isaacson, director of research at the Institute for Neurodegenerative Diseases in Boca Raton, Florida. He was not involved in the study.

“First, we recommend testing for omega-3 fatty acid levels — there are finger-prick tests you can buy online which are accurate — and then you should continue to test. You don’t want to take fish oil if you don’t need it,” he said.

Isaacson recommends trying to get your omega-3 fatty acids from food sources and says sardines and wild-caught salmon are the best sources, as they are high in these healthy unsaturated fats and lower in mercury. Farm-raised salmon is not the best choice, he said, due to impurities in the water in which they are raised.

Lake trout, mackerel, herring and albacore tuna are also good sources, he said. However, due to the mercury levels in large fish such as tuna, he recommends consumption of albacore tuna should be kept to twice a week.

Algae and seaweed are decent nonfish sources of omega 3s as well. Chia seeds, edamame (soy beans), flaxseed, hempseeds and walnuts are other plant-based options that are high in omega-3s. But the fatty acids are a different form than those found in fish. Studies have found plant-based omega-3s may be harder to metabolize in people with higher levels of omega-6s, another kind of unsaturated fats that’s found primarily in vegetable oils.

If supplements are needed

Prescription omega-3 fatty acids are superior to over-the counter options, experts say, due to their pureness and quality. But prescribed supplements can be expensive. For people who decide they want to purchase over-the-counter omega-3s, Isaacson provides these tips to his patients.

First, freshness of the fish oil is key, he said, adding that “buying from an online or retail superstore, such as Amazon or Costco, isn’t the best idea.”

“We recommend buying it from only a handful of reputable companies, and from their specific website,” Isaacson said. “The difference in quality between fish oil stored in a hot warehouse that’s close to expiration and fish oil that’s recently been produced, sent directly from the company, and kept in the home refrigerator is night and day.”

The US Food and Drug Administration doesn’t monitor the supplement industry to assure each vitamin or mineral actually contains what it says on the label, nor does the federal agency test to see whether the ingredients are contaminated with bacteria, heavy metals, pesticides, plastic residues and other impurities.

However, there are some companies that have stepped into that role by testing various supplements and even some pharmaceuticals, so look for their labels on the supplements before purchase. The nonprofit organization US Pharmacopeia, or USP, sets the most widely accepted standards for supplements, experts say, but ConsumerLab.com and NSF International also do third-party testing.

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