- Omega-3 fatty acids, found abundantly in oily fish, walnuts, and flaxseeds, are associated with reduced inflammation, lower triglycerides, and cardiovascular benefit.
- Getting omega-3 from food sources is generally preferred over supplements, the evidence for dietary omega-3 is considerably stronger than for capsules.
- A large 2024 study found that fish oil supplements in people without existing heart disease were associated with a modestly higher risk of atrial fibrillation and stroke, a finding that warrants careful consideration.
- For people with existing cardiovascular disease or significantly elevated triglycerides, omega-3 supplements may still have a role, but this is a conversation to have with your doctor.
- A prescription-strength omega-3 medication called icosapent ethyl (Vascepa) has demonstrated meaningful cardiovascular benefit in specific high-risk patients, this is quite different from over-the-counter fish oil supplements.
- Most Western diets are heavily weighted toward omega-6 fatty acids, shifting the balance toward more omega-3 through food is a straightforward and well-supported goal.
Fish oil is one of the most widely taken supplements in the world. Millions of people take it daily in the belief that it is broadly good for the heart, an understandable assumption given how consistently omega-3 fatty acids have been associated with cardiovascular benefit in research. But the picture is more nuanced than the supplement aisle would suggest, and the distinction between getting omega-3 from food versus from a capsule matters more than most people realise.
This article explains what omega-3 fatty acids are, what they do for the heart, what the evidence actually shows about supplements, and how to think about this topic in the context of your own health.
What Are Omega-3 Fatty Acids?
Omega-3 fatty acids are a family of polyunsaturated fats that the body cannot produce on its own, they must come from food or supplements. There are three main types relevant to heart health:
| Type | Main Sources | Notes |
|---|---|---|
| EPA (eicosapentaenoic acid) | Oily fish, salmon, sardines, mackerel, trout, herring | Most directly linked to cardiovascular and anti-inflammatory effects |
| DHA (docosahexaenoic acid) | Oily fish, algae-based supplements | Important for heart and brain function; also found in krill oil |
| ALA (alpha-linolenic acid) | Flaxseeds, chia seeds, walnuts, canola oil | Plant-based source; the body converts small amounts to EPA and DHA |
EPA and DHA, found primarily in oily fish, are the forms most studied in cardiovascular research. ALA from plant sources offers some benefit, but the conversion to EPA and DHA in the body is limited, which is why oily fish features so prominently in heart-healthy dietary recommendations.
What Omega-3s Do for the Heart
The cardiovascular benefits associated with omega-3 fatty acids, particularly from dietary sources, are reasonably well established and include several interconnected effects.
Triglyceride reduction is the most consistent finding. Omega-3 fatty acids reliably lower triglyceride levels in the blood, elevated triglycerides are associated with increased cardiovascular risk and are often seen alongside other metabolic issues such as insulin resistance and low HDL cholesterol.
Inflammation reduction is another key mechanism. Chronic low-grade inflammation plays a central role in atherosclerosis, the build-up of plaques inside arteries. Omega-3s have well-documented anti-inflammatory properties that may help slow this process over time.
Blood pressure appears to fall modestly with regular omega-3 intake, and there is some evidence of benefit for blood vessel function and flexibility. There has also been interest in omega-3s and heart rhythm, though as discussed below, the picture here is more complex than initially hoped.
The Omega-3 to Omega-6 Balance
Omega-6 fatty acids, found in vegetable oils, nuts, seeds, and many processed foods, are also essential polyunsaturated fats. In modest amounts and from whole food sources, they are part of a healthy diet. The issue is one of proportion.
The typical modern Western diet contains far more omega-6 than omega-3, estimates suggest ratios of around 15:1 or higher, compared to a ratio closer to 4:1 that most nutrition researchers consider more favourable. This imbalance is primarily driven by heavy consumption of processed foods, seed oils, and packaged snacks, combined with relatively low intake of oily fish.
The practical goal is not to dramatically reduce omega-6, it’s to increase omega-3 intake through food, which naturally shifts the balance. Eating oily fish twice a week, adding walnuts or flaxseeds to meals, and using olive oil as the primary cooking fat are all steps that move the ratio in a healthier direction without requiring precise tracking.
The Evidence on Fish Oil Supplements, A More Complicated Picture
Here is where the story becomes more nuanced, and where it’s worth being honest about what the evidence actually shows, rather than what many supplement labels imply.
For years, fish oil supplements were widely assumed to provide the same cardiovascular benefits as eating oily fish. The evidence from dietary studies was so consistent that it seemed reasonable to expect supplements to follow suit. Large clinical trials have not reliably confirmed that assumption.
The BMJ Study, Atrial Fibrillation and Stroke Risk
A significant study published in BMJ Medicine analyzed data from over 415,000 participants in the UK Biobank and found that among people without existing cardiovascular disease regular fish oil supplement use was associated with a 13% higher risk of developing atrial fibrillation (an irregular heart rhythm) and a 5% higher risk of stroke compared to non-users.
This is a meaningful finding that deserves acknowledgement. Atrial fibrillation, often abbreviated to AF, is the most common heart rhythm disorder and is itself a significant risk factor for stroke. A supplement taken with the intention of protecting the heart potentially increasing AF risk in otherwise healthy people is not a trivial concern.
The BMJ study was observational, meaning it tracked what happened to people who chose to take supplements, rather than randomly assigning them to do so. This means it cannot definitively prove that fish oil caused the increased risk. People who take supplements may differ in other ways from those who don’t.
However, the finding is consistent with signals from several other large trials and is large enough to take seriously. It has shifted thinking among many cardiologists away from routinely recommending fish oil supplements for the general population.
What About Krill Oil and Cod Liver Oil?
Krill oil is derived from small crustaceans and contains EPA and DHA in a phospholipid form, which some research suggests may be absorbed more readily than the triglyceride form found in most fish oil capsules. It also contains astaxanthin, a natural antioxidant. However, the clinical evidence base for krill oil specifically, particularly for hard cardiovascular endpoints like heart attacks and strokes, is considerably smaller than for standard fish oil, and no firm conclusions can be drawn about whether it offers advantages.
Cod liver oil provides EPA, DHA, and also vitamins A and D. The vitamin D component may be of interest for some people, but the high vitamin A content means that excessive doses carry risk, and the dosing guidance on the label warrants attention. It is not interchangeable with standard fish oil for cardiovascular purposes.
Vascepa, When a Prescription Omega-3 Is Different
It is worth distinguishing standard over-the-counter fish oil from a prescription medication called icosapent ethyl (Vascepa). This is a highly purified form of EPA, not a combination of EPA and DHA, and it has been specifically studied in high-risk cardiovascular patients.
The REDUCE-IT trial found that in patients with elevated triglycerides who were already on statin therapy, Vascepa reduced the risk of major cardiovascular events, including heart attack and cardiovascular death, by approximately 25% compared to placebo. This is a clinically significant result and represents one of the more compelling cardiovascular outcome findings in recent years.
Vascepa is a prescription medication used for a specific indication, it is not a substitute for over-the-counter fish oil, and the REDUCE-IT results cannot be extrapolated to standard supplements. If you have significantly elevated triglycerides and are on statin therapy, it is worth asking your cardiologist whether Vascepa is appropriate for your situation.
Food First, The Practical Takeaway
The consistent message from the evidence, and the position most cardiologists would take, is that getting omega-3 from food is preferable to relying on supplements. Oily fish delivers EPA and DHA alongside high-quality protein, vitamin D, selenium, and a range of other nutrients that supplements do not replicate. The epidemiological evidence linking regular fish consumption to cardiovascular benefit is considerably stronger and more consistent than the evidence for supplements.
- Eat oily fish twice a week. Salmon, sardines, mackerel, trout, and herring are all excellent sources of EPA and DHA. Canned versions are nutritionally comparable to fresh and considerably more convenient and affordable.
- Add walnuts to your routine. A small handful provides ALA alongside fiber and healthy fats. Works well as a snack or added to oats, salads, or yogurt.
- Include flaxseeds or chia seeds. Both are good plant-based sources of ALA. A tablespoon added to oats, a smoothie, or yogurt integrates easily into daily eating.
- Use olive oil as your primary cooking fat not a direct omega-3 source, but it supports the overall healthy fat balance and reduces displacement by less favourable oils.
- Reduce heavily processed foods these are typically high in omega-6 from seed oils and contribute to the unfavourable ratio that characterises many modern diets.
Should You Take Fish Oil Supplements?
For most people without existing heart disease, the current evidence does not strongly support routine fish oil supplementation, and the BMJ finding around AF risk is a reason for genuine caution rather than dismissal. Food sources remain the more evidence-supported approach.
For people who have been diagnosed with cardiovascular disease, have significantly elevated triglycerides, or have specific conditions where omega-3 supplementation has been discussed with their doctor, the picture may be different. This is not a one-size-fits-all recommendation, and individual clinical circumstances matter considerably.
If you are currently taking fish oil supplements and are unsure whether they are appropriate for your situation, particularly if you have a history of AF, are at risk of stroke, or have other cardiovascular conditions, it is worth raising this with your doctor at your next visit.
Conclusion
Omega-3 fatty acids are genuinely important for cardiovascular health, but the story of how best to get them is more nuanced than the supplement industry’s messaging suggests. The evidence for oily fish as a regular part of the diet is strong and consistent. The evidence for over-the-counter fish oil supplements is mixed, and recent large studies have raised legitimate questions about their use in people without existing heart disease.
For most people, the most practical and well-supported approach is to eat oily fish regularly, include other omega-3 rich foods in the diet, and reserve the supplement conversation for situations where a doctor has specifically identified a clinical need. As with most things in nutrition, the overall pattern of eating matters more than any single supplement.
