GUANGZHOU, China — Fish oil supplements have long been touted as a way to protect the heart. However, a major new study finds that regularly taking fish oil supplements when you’re already in good health might actually increase the risk of atrial fibrillation and stroke.

Surprisingly, the same supplements may benefit those who already have cardiovascular issues like AFib or heart failure.

The research, published in BMJ Medicine, tracked over 400,000 adults in the UK Biobank study for nearly 12 years. Scientists looked at whether participants regularly used fish oil supplements and monitored them for new cases of AFib, heart attacks, strokes, heart failure, and deaths from all causes.

For people starting off without any diagnosed heart conditions, regularly taking fish oil displayed a link to a 13-percent higher risk of developing a new case of AFib compared to non-users. Fish oil users also had a five-percent higher risk of stroke. However, for relatively healthy individuals, fish oil supplements did not raise or lower the risk of heart attacks or death.

The story was very different for those who already had cardiovascular disease at the study’s outset. Among participants with existing AFib, regular fish oil use was associated with an eight-percent lower risk of having a major heart event like a heart attack or stroke. Fish oil users with AFib also had a nine-percent lower risk of death compared to non-users.

For those starting with heart failure, taking fish oil was tied to a nine-percent lower risk of dying during the study period compared to heart failure patients not using the supplements.

So what’s going on here? Why would fish oil potentially increase cardiac risks for healthy people but decrease them for those already dealing with heart issues?

Omega-3 supplements
A major new study finds that regularly taking fish oil supplements when you’re already in good health might actually increase the risk of atrial fibrillation and stroke. (Credit: Intermountain Healthcare)

The researchers suggest a few possible explanations. For one, the positive and negative effects may be related to the specific dose and formulation of omega-3 fatty acids found in different fish oil products. Higher doses could be problematic for the heart rhythm, while lower doses provide anti-inflammatory benefits.

It’s also possible that fish oil has different biological impacts depending on whether the user has existing heart disease. In those with a clean cardio bill of health, omega-3 fatty acids may adversely alter cell membranes and molecular pathways in a way that raises AFib and stroke risk. In people with established cardiovascular conditions, however, those same fatty acids might improve blood flow, reduce clot risk, and prevent a disease’s progression.

The study authors emphasize that more research is still necessary. We don’t yet fully understand the precise mechanisms at work or whether factors like genetics, medications, diet, and lifestyle influence how people respond to fish oil supplementation.

For now, the findings suggest a nuanced view. Taking fish oil likely does not provide meaningful protection against heart disease for lower-risk individuals. However, for those already dealing with heart issues, the supplements could help prevent a worsening of their condition.

As with many aspects of health and nutrition, there’s no one-size-fits-all effect of fish oil. The impacts appear to be a double-edged sword, with potential pros and cons depending on someone’s starting point. More personalized recommendations may be needed about whether or not to take these wildly popular omega-3 supplements.

StudyFinds Editor Chris Melore contributed to this report.

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