Up to 20M Healthy Americans Who Take Common Supplement May Be at Raised Risk of Stroke and Atrial Fibrillation, Study Finds

Think about your daily supplement routine for a moment. If you’re among the millions of Americans who reach for a fish oil capsule each morning, you probably do it with good intentions – and you’re far from alone. The supplement has carried an almost unassailable reputation for decades, closely tied in the popular imagination to ideas of heart protection, brain health, and longevity. It sits in medicine cabinets from coast to coast, right next to the vitamins.

But the science behind those little softgels has always been more complicated than the marketing suggests. And a major piece of research, now thoroughly examined by cardiologists across the country, is giving millions of otherwise healthy people real reason to pause. The question isn’t whether omega-3 fatty acids are valuable. They clearly are. The question is whether swallowing them in pill form does what most people assume it does – and, critically, whether it could actually be doing something very different.

The answer, it turns out, depends almost entirely on who is taking them.

How Popular Fish Oil Really Is

According to a February 2026 Consumer Reports survey of 2,272 U.S. adults, fish oil supplements are among the five most popular supplements in the country, with about 1 in 5 Americans saying they’ve taken fish oil in the past 12 months. That translates to a staggering number of people. Most take it in hopes of preventing heart disease – the leading cause of death in the U.S. – and omega-3 supplements are among the most common type of dietary supplement used by U.S. adults, particularly those 60 and over, according to the Centers for Disease Control and Prevention.

About 20% of adults over age 60 take the supplements regularly, with the aim of supporting heart health. That demographic – older adults taking fish oil for cardiovascular protection – is precisely the group the latest research puts in the spotlight. The global fish oil products market is valued at $2.9 billion in 2025, a figure that reflects just how deeply this supplement has embedded itself in everyday health routines.

So what exactly is in the capsule? Fish oil primarily contains two omega-3 fatty acids: docosahexaenoic acid, known as DHA, and eicosapentaenoic acid, known as EPA. DHA supports brain cell structure and heart cell membrane health, while EPA plays a more active role in the bloodstream, helping to manage inflammation. These are fatty acids your body cannot manufacture on its own, which is why diet or supplementation is required to obtain them.

What the Research Found – and Who It Affects

The study drew on data from the UK Biobank, enrolling participants between January 2006 and December 2010, with follow-up extending to March 2021. A total of 415,737 participants, aged 40 to 69, were included. During an average monitoring period of nearly 12 years, 18,367 participants developed atrial fibrillation, 22,636 had a heart attack, a stroke, or developed heart failure, and 22,140 died. The research team then mapped which of those participants regularly used fish oil supplements and tracked how things unfolded.

The findings split sharply depending on whether participants had existing cardiovascular disease or not. 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 in the journal BMJ Medicine.

That fish oil stroke risk finding is exactly what drew so much attention. The study concluded that regular use of fish oil supplements might be a risk factor for atrial fibrillation and stroke among the general population – the same population that has been buying fish oil by the billion capsule for decades, assuming it was helping their heart.

To understand why this matters so much, it helps to understand what atrial fibrillation actually is. Atrial fibrillation, often called AFib, is the most common cardiac arrhythmia encountered in clinical practice. In plain terms, it’s an irregular heartbeat where the upper chambers of the heart quiver instead of beating in a coordinated rhythm. That might sound manageable, but the downstream consequences are serious. The chief hazard of atrial fibrillation is embolic stroke – a stroke caused when a blood clot travels to the brain – with the risk increased 4 to 5 fold compared to people with a normal heart rhythm.

The prevalence of atrial fibrillation in the United States is projected to double between 2010 and 2030, which means the potential interaction between a growing condition and one of the most widely consumed supplements in the country is a public health concern worth taking seriously.

The Flip Side: Benefits for Those Already Sick

The picture is not entirely negative, and that distinction matters enormously. The same study found that fish oil behaved very differently in people who already had cardiovascular disease when they enrolled. For participants diagnosed with cardiovascular disease, regular use of fish oil supplements was beneficial in slowing down the transition from atrial fibrillation to major adverse cardiovascular events, or from heart failure to death.

This is a meaningful distinction. For someone managing an established heart condition, the supplement appears to offer genuine protective benefits against the disease getting worse. That is very different from using it preventively in a healthy person hoping to avoid heart disease in the first place.

The researchers framed their conclusion carefully. They urged caution when using fish oil or omega-3 fatty acid supplements for primary prevention – meaning use in healthy people without existing disease – due to potential adverse effects and uncertain cardiovascular benefits.

What Cardiologists Are Saying

The reaction from practicing cardiologists has been pointed out. Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver, said, “Over-the-counter fish oil is very seldom recommended, is in none of the guidelines from professional medical societies,” adding that this is what most people take.

Freeman noted that “studies over the last 10 years have not been very positive for over-the-counter fish oil,” explaining that “fish oil was either having no benefit or in some cases it may harm, such as with stroke and AFib.”

Prescription versions of fish oil, such as Vascepa and Lovaza, are used to counter risk factors like high triglycerides in people with cardiovascular disease risk. But Freeman noted that “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.”

That’s a critical distinction most people don’t know: there is a significant difference between pharmacy-grade, prescription omega-3 formulations prescribed by a doctor for a specific condition and the fish oil capsules sitting on supermarket shelves next to the multivitamins. The latter are not the same product, not held to the same standards, and not what medical guidelines are written around.

A 2025 analysis published in the Journal of the American Heart Association noted that meta-analyses of randomized trials with omega-3 products found an increased risk of atrial fibrillation, lending further weight to the growing body of evidence that the fish oil stroke risk and AFib link is not a one-off finding.

The Observational Study Limitation

Before drawing any absolute conclusions, it’s important to understand what kind of study this is. The UK Biobank research is an observational cohort study – it tracked what happened to a large group of people over time, but it did not randomly assign anyone to take or not take fish oil. That means it can identify associations, not prove that fish oil directly caused the increased AFib and stroke risk. As the BMJ Group noted in its press release, the study drew on 415,737 UK Biobank participants aged 40 to 69 and assessed the potential role of supplements on the risk of progressing from good heart health to atrial fibrillation and beyond – but findings from an observational study cannot prove cause and effect, only a link between the two.

There are real-world confounders (factors that could interfere with the results) here. People who take fish oil supplements may differ from non-users in ways the study couldn’t fully account for – their overall health behaviors, other supplements they take, their dietary patterns. It’s possible that some people started taking fish oil specifically because they felt their heart health was already declining, which could skew the results toward apparent harm.

Industry groups, including the Global Organization for EPA and DHA Omega-3s, noted that the results of this observational study pertaining to healthy participants contradict the overwhelming majority of prior evidence. The organization has separately pointed out that little or no increase in AFib risk has been seen with typical daily supplementation dosages below one gram.

Clinical trial results on fish oil have been mixed, with a few recent studies suggesting some potential harm, leading scientists to conclude that the supplement’s usefulness in heart disease prevention is uncertain, at best.

The Dose and Purity Question

Not all fish oil supplements are equal, and dose matters. High supplemental doses above 3 grams per day of combined EPA and DHA may increase bleeding time and interact with anticoagulant (blood-thinning) medications. If you’re already taking a blood thinner like warfarin or a newer anticoagulant, adding high-dose fish oil without telling your doctor is worth a conversation.

Quality is another concern. Consumer Reports’ 2026 testing of 20 popular fish oil brands found that while 16 met all safety and quality standards, some products showed concerning results, including oil that may have gone rancid. Rancid fish oil doesn’t just taste unpleasant. Some studies suggest that potential risks of fish oil supplements include oxidation of the oil in capsules, which could increase the risk of clogged arteries.

Consumer Reports concluded that these supplements probably have only minimal health benefits for most people, and that for most people, fish oil pills won’t significantly reduce the risk of heart attacks and strokes, based on results of major clinical trials.

Read More: Heart-Healthy Supplements to Consider (and Two to Avoid)

What to Do Now

The research doesn’t say that everyone should stop taking fish oil immediately. What it does say is that the decision to take it deserves more thought than it typically gets.

If you have existing cardiovascular disease, there may still be a role for omega-3 supplements in certain cases, particularly for patients at high risk of future cardiovascular events. However, the evidence is mixed and depends heavily on the formulation and dose used. Some studies, including large randomized trials, have found modest reductions in cardiovascular events in high-risk populations, while others have found no significant benefit. For this reason, decisions about continued use should be made with a cardiologist rather than independently.

If you’re a healthy adult without any diagnosed cardiovascular condition and you’re taking fish oil primarily as a precaution, the current weight of evidence suggests the benefit is far from certain, and there’s a real fish oil stroke risk to weigh against the hoped-for upside. The better path is well-established. According to Donald Lloyd-Jones, MD, principal investigator for the Framingham Heart Study and scientific lead for the American Heart Association, years of nutrition research have demonstrated that diets high in omega-3 fatty acids seem to be better for cardiovascular health than diets with low levels. The AHA’s own guidance emphasizes eating fatty fish as the best source of omega-3s rather than relying on supplements. Salmon, sardines, mackerel, and herring all deliver the same EPA and DHA your supplement contains, along with protein, selenium, and other nutrients that support cardiovascular health in ways a capsule simply cannot replicate.

Research suggests that omega-3s from whole foods may offer greater benefits than those taken in pill form. For most people, getting omega-3s by eating fish such as salmon or sardines a couple of times a week is the recommended approach. Walnuts, chia seeds, and flaxseed oil offer plant-based sources of the related omega-3 ALA, which the body can partially convert.

If you’re currently taking fish oil and have questions, the most practical step is straightforward: bring the bottle to your next medical appointment. Tell your doctor what you’re taking, why you started, and ask whether the evidence actually supports it in your specific situation. As Dr. Freeman put it, “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.” Over-the-counter doesn’t mean risk-free, and popular doesn’t mean proven.

Read More: Why This Oil is the New Low Saturated Fat Alternative to Olive Oil

Disclaimer: The author is not a licensed medical professional. The information provided is for general informational and educational purposes only and is based on research from publicly available, reputable sources. It is not intended to constitute, and should not be relied upon as, medical advice, diagnosis, or treatment. Always consult a licensed physician or other qualified healthcare provider regarding any medical condition, symptoms, or medications. Do not disregard, avoid, or delay seeking professional medical advice or treatment because of information contained herein.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.