Many people take fish oil supplements to protect their hearts either as a prescription or over-the-counter drug. In recent years, however, researchers have questioned not only whether the supplements actually improve heart health, but whether they pose a health risk in high doses.

Fish is a well-known source of omega-3 fatty acids – particularly salmon, sardines, and mackerel. Eating fish at least twice a week has been linked to reductions in heart attacks, strokes, and cardiovascular deaths. According to a Harvard studyEating two servings of oily fish a week reduced the risk of death from heart disease by a third.

However, when it comes to consuming fish oil supplements, recent studies show more potential risks than benefits.

Prescription fish oil pills are often prescribed to reduce a person’s triglycerides, a blood fat that, in high concentrations, increases a person’s risk of heart attack and stroke.

Some data has shown that high doses of a fish oil supplement increase the risk of atrial fibrillation, a common heart rhythm disorder, while providing little heart health benefits. A new analysis seems to confirm this increased risk.

The analysis, published in the European Heart Journal – – In cardiovascular pharmacotherapy, five clinical studies on the risk of atrial fibrillation in patients taking fish oil were re-performed. Overall, cardiac patients who took fish oil at doses between 0.84 and 4 grams per day had a greater than 33% increased risk of developing atrial fibrillation compared to patients given a placebo.

Atrial fibrillation, or AFib, is an irregular and often rapid heart rate caused by electrical signal problems in the upper chambers of the heart. The condition is not immediately life-threatening, according to the Mayo Clinic, but it can cause blood clots to develop in the heart. These clots can get to other parts of the body and block blood flow. Finally, AFib can also lead to heart failure.

The increased risk was consistently observed in all studies included in the analysis. However, there were no heart health benefits.

The researchers said there were more cases of AFib in the patients who took the fish oil than in the patients in the placebo group.

Although the risk was not statistically significant in any of the individual studies, the pooled analysis showed that patients taking the supplement were 37% more likely to develop AFib than those taking placebo.

Also of note, only one of the studies showed a reduction in the risk of other heart diseases. That study included a specific product called Vascepa, which is icosapent ethyl, just one type of omega-3 fatty acid found in fish oil. The risk of cardiovascular events, including heart attack, stroke, and death, due to cardiovascular causes was reduced by 25%.

Even in this study, the AFib risk increased by 35% in the group taking Vascepa.

Another Cleveland Clinic study was canceled last fall because prescription doses not only did not reduce major cardiac events, but appeared to increase the risk of atrial fibrillation.

Supplementing with fish oil remains controversial as research remains inconsistent. Some studies have also been done on fish oil supplements. A 2018 study found that a highly purified form of fish oil had cardiovascular benefits when compared to a mineral oil placebo. However, many cardiovascular health experts questioned the study’s methodology. The fact that mineral oil, which can affect cholesterol and markers of inflammation, was the comparison may have resulted in the fish oil supplements being exaggerated.

Other studies have questioned whether fish oil supplements have any cardiovascular benefits.

A 2108 study published in JAMA Cardiology looked at 10 fish oil supplement studies in 77,917 older adults at high risk for cardiovascular disease and found no significant protection against “major vascular events”. Participants ingested between 226 milligrams and 1,800 milligrams of omega-3 fatty acids per day.

A 2013 and 2018 study published in the New England Journal of Medicine also showed that supplementation did not reduce cardiovascular events or deaths. In this study, it was found that people who do not eat fish may experience some reduction in risk when taking the supplement.

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