Do fish oil supplements raise the risk of heart disease?

If you take fish oil supplements, it might be because you’ve heard they’re a rich source of omega-3s, which have been linked to a lower risk of coronary heart disease when eaten as part of a healthy diet.

But new research suggests that taking these supplements may increase your risk of a stroke or atrial fibrillation (an abnormal heart rhythm) if you do not already have heart or circulatory disease.

Several UK news outlets reported on the study of over 400,000 British people published in BMJ Medicine, which was carried out by researchers from Sun Yat-Sen University in China.

The researchers looked at data over an average of 12 years to see how fish oil supplements affected the progression of heart and circulatory diseases in healthy people compared to those who had diagnosed heart conditions.

They found healthy people who said they ‘regularly’ used fish oil supplements were 13 per cent more likely to develop atrial fibrillation compared to those who did not. They were also 5 per cent more likely to have a stroke.

However, for people with diagnosed heart conditions, the results suggested the supplement reduced the chance of having other heart issues.

For those with atrial fibrillation, taking fish oil lowered the likelihood of having a heart attack by 15 per cent compared to those who did not take the supplement.

A similar positive effect was seen for people with heart failure. Those who took fish oil supplements had a 9 per cent lower chance of death compared to those who did not.

As the study was observational, the findings do not prove cause and effect – just a link between the two.

But it piqued media interest because the health benefits of taking fish oil or other omega-3 supplements – rather than eating omega-3 rich foods – have been widely debated, with previous research giving mixed results.

For example, a 2021 review of seven studies published in the journal Circulation suggested that taking omega-3 supplements came with an increased risk of atrial fibrillation.

But a 2020 review of the Vitamin D and Omega-3 Trial (VITAL) in Circulation Research journal found that the risk of atrial fibrillation did not go up in healthy adults who took omega-3 supplements compared to those given a dummy supplement.

And a 2020 analysis of 16 trials in Pharmacological Research suggested that omega-3 supplements reduced the risk of dying from heart disease in people who have a heart condition.

As a result, current National Institute for Health and Care Excellence (NICE) guidelines do not recommend taking fish oil supplements to prevent heart and circulatory diseases.

What do the researchers say?

The researchers looked at data on 415,737 people, aged 40-69, who were enrolled in the UK Biobank study and did not have heart and circulatory disease at the beginning of the research.

At the start of the study, 31 per cent said they ‘regularly’ took fish oil supplements.

These people were more likely to be female, over 65 and White, and less likely to smoke.

The researchers confirm that, as an observational study, it does not prove cause and effect.

But they conclude that, while fish oil supplements may be a risk factor for atrial fibrillation and stroke in healthy people, they may prevent heart conditions from getting worse for those who already have atrial fibrillation or heart failure.

However, it’s not clear why the supplements may have this effect.

They suggest that further studies are needed to find out how and why fish oil supplements influence the risk of these heart conditions.

How good was the research?

The researchers admit that they have no information on what fish oils and omega-3s the supplements contained and what doses people took.

Participants were only asked if they ‘regularly’ used fish oil supplements at the beginning of the study. This could have been daily for some people, but a few times a week for others.

Also, we do not know how many people carried on taking the supplements throughout the study. Furthermore, as the study was observational, there may have been other factors affecting participants’ heart and circulatory disease risk.

For example, the study found people who took fish oil supplements were less likely to smoke.

As smoking increases the risk of a heart attack, these people would have been at lower risk of having a heart attack than those that smoked.

One strength of the study is its size, with data from over 400,000 people.

However, this group was not diverse, with 95 per cent of participants of White ethnicity.

This means the results could be different for people of other ethnicities.

How good was the media coverage?

The study was reported by lots of UK newspapers, including The Telegraph, The Sun, The Times and The Guardian.

The Telegraph and The Sun both said incorrectly the research studied the effects of “cod liver oil supplements”.

However, the study asked people if they took any form of fish oil supplement, not just cod liver oil.

The Telegraph and The Sun also mentioned that the research looked at people who took a daily supplement.

This is not accurate, as the researchers did not know how often people took the supplements, only that they took them ‘regularly’.

Most of these outlets made it clear that the study was observational and could not establish cause and effect.

However, The Times stated that: “For those with pre-existing poor heart health, however, fish oil supplements slowed the progression of cardiovascular disease.”

This suggests that the study found supplements can directly slow the progression of heart disease, which it did not.

Finally, The Guardian accurately explained that the study lacked diversity.

However, their headline ‘Fish oil may increase risk of heart conditions and stroke, study finds’ does not make it clear that the risk was only higher in healthy people, which may have led to confusion.

The BHF verdict

We know food high in omega-3s can help lower your risk of heart and circulatory disease. But this study shows the jury is still out on the benefits of taking supplements, like fish oil, that contain omega-3s.

“This research should not be concerning to people who regularly take fish oil supplements, but it’s also not a green light to start taking them to prevent heart and circulatory diseases,” said Tracy Parker, a Senior Dietitian at British Heart Foundation, in a statement responding to The Guardian’s article.

Instead, people should look at their whole diet when aiming to reduce their risk of heart disease, she advised.

“A healthy, balanced diet which includes oily fish can provide you with omega-3 and all the other nutrients essential for keeping your heart healthy. The traditional Mediterranean diet has been shown time and again to reduce the risk of heart attack or stroke,” she said.

• Learn more about the Mediterranean diet.

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