Omega-3 oils, typically found in oily fish and fish oil supplements, are often said to have numerous health benefits, such as reducing the risk of heart attacks, dementia and joint pain.

But recent research published in the journal BMJ Medicine shows that while fish oil supplements could reduce the risk for those who already have cardiovascular disease, they may increase the risk of someone developing a heart condition or stroke in the first place.

So are omega-3s good for you, and does it matter how you get them?

Why do you need omega-3s?

Omega-3s are essential fatty acids, which are important for health. Your body cannot make them, so you have to get them from your diet. There are three main types of omega-3s. Alpha-linolenic acid (ALA) is necessary for your body to make eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are important for your heart, blood vessels, lungs and the immune and hormone systems. DHA is also important for the development of the retina, brain and nervous system in babies.

But as people can convert only small amounts of ALA into EPA and DHA, they need to eat foods containing them. 

OK, so how do you get omega-3s?

Oily fish such as mackerel, salmon and sardines are a rich source of EPA and DHA omega-3s. White fish such as cod, haddock and plaice, and shellfish also contain omega-3s but at much lower levels than oily fish. If you do not eat fish you can get omega-3s from flaxseed, chia seeds, walnuts, rapeseed, soya beans and the oils made from them.

Many people take fish oil supplements or vegetarian omega-3 supplements, which contain microalgae oil.

Does it matter if you take supplements rather than eating fish?

Current guidelines recommend the latter.

The NHS recommends eating at least one portion of oily fish a week to help prevent the development of cardiovascular disease. However, pregnant women or those breastfeeding should not have more than two portions, or 140g a week.

By contrast, in the UK, National Institute for Health and Care Excellence guidelines do not recommend the use of omega-3 supplements to prevent cardiovascular disease or prevent another heart attack, unless your GP prescribes them for high levels of triglyceride. 

The British Dietetic Association, which represents UK dietitians, says: “Omega-3 supplements are not recommended in the UK general population. This is because evidence of benefits is inconclusive.”

What about this new study?

In brief, a team of researchers monitored the health of more than 400,000 participants in the UK Biobank (a biomedical database) for an average of 12 years. They looked at the impact of taking fish oil supplements on developing heart conditions such as atrial fibrillation (irregular heartbeat), heart attack, stroke and heart failure. They also assessed whether these supplements affected the progression of heart conditions.

They found that regular use of fish oil supplements was associated with a 13% heightened risk of developing atrial fibrillation and a 5% heightened risk of having a stroke. But the study also showed that these supplements were associated with 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.

But this study only looked at omega-3 supplements, so cannot tell us about the risks and benefits of eating oily fish itself.

How does this fit with other research?

Previous studies have found little or no evidence that supplements containing the omega-3s EPA and DHA lowered the risk of a heart attack, stroke or dying from heart disease.

And a large study conducted in the US found fish oil supplements were only beneficial for people who did not eat fish.

However, studies have found high levels of omega-3s are associated with lower risks of dementia – although how participants got these omega-3s is not clear, and the study does not prove cause and effect – while research suggests consuming oily fish could help reduce inflammation and pain for patients with rheumatoid arthritis and lupus.

Research from 2022 found that among older adults, taking regular fish oil supplements was significantly associated with a lower risk of all-cause dementia, as well as vascular dementia, frontotemporal dementia and other dementia, but not Alzheimer’s disease.

Should I stop taking omega-3 supplements or start eating oily fish?

Tom Sanders, a professor emeritus of nutrition and dietetics at King’s College London, said small amounts of long-chain omega-3 fatty acids had permitted health claims for maintenance of a healthy heart and for normal brain and visual development in infants. 

But, he said, trials in relation to heart disease prevention had mainly been in people with type 2 diabetes or those who have had a cardiovascular event. What is more, while high doses of fish oil supplements have been associated with decreased cardiovascular mortality, most trials using lower doses show no such benefit.

“Current guidelines for cardiovascular disease prevention do encourage fish consumption but not fish oil supplements,” he said.

Nathan Davies, the clinical nutrition programmes lead at University College London, said there was no evidence that eating fish was damaging to health.

“Eating a healthy diet is always preferable to taking supplements, and following NHS advice to eat oily fish on a weekly basis is beneficial in relation to omega-3 intake, vitamin D and other micronutrients,” he said.

“Where people have specific dietary requirements supplements can be beneficial, but for the vast majority of the population it is far better to eat a varied diet.”

However, Davies said there was no need for anyone taking omega-3 supplements to discontinue them.

And if you are worried about your heart, you should seek medical advice and not try to self-medicate with supplements, he added.