Minimal evidence to show omega-3 prevents heart dise...

"It's oil a myth," states The Sun, while the Daily Telegraph encourages people to "buy more vegetables instead of omega-3 supplements to improve heart health".

These are just a couple of the many headlines reporting on a recent large-scale review investigating the effects of increasing omega-3 intake on heart health.

Omega-3 refers to 3 types of fatty acids found in fish and some plants. There have been claims that taking omega-3 supplements can reduce the risk of a range of serious diseases, such as heart disease and stroke. Despite there actually being little evidence for this, the global market for omega-3 supplements is now estimated to be worth around $33 billion.

Using data collected from more than 100,000 people, UK researchers found little or no evidence that increasing the intake of omega-3 benefits heart health.

However, experts believe that eating oily fish, which is rich in omega-3, as part of a healthy diet is still good for the heart as well as for overall health. As lead author Dr Lee Hooper said in an associated press release: "Oily fish is a healthy food."

Where did the story come from?

The study was carried out by researchers from the University of East Anglia, Durham University and the University of Manchester. It was published in the peer-reviewed Cochrane Database of Systematic Reviews and funded by the National Institute for Health Research.

While there was widespread coverage in the UK media, not all the headlines were entirely accurate. Some, such as The Sun's, gave the impression that taking omega-3 supplements can actually make your health worse by reducing the amount of healthy cholesterol in the body. But the research did not show any negative effects of taking omega-3 supplements – it just found no benefits.

None of the reports made it clear there are still health benefits associated with eating oily fish.

What kind of research was this?

This study was a Cochrane systematic review assessing the effects of an increased intake of omega-3 on death from any cause, on cardiovascular outcomes such as heart attacks or strokes, and on fat levels in the blood.

Omega-3 fats are essential fatty acids – acids the body needs to stay healthy. However, the body cannot produce them, so we must get some from dietary sources such as fish and plants.

This review was prompted by the widespread belief that taking omega-3 supplements is a simple way to protect the heart. Some experts were not convinced there was enough evidence to support this belief.

To test it, the Cochrane collaboration – a non-profit, non-governmental organisation that uses experts from around the world – conducted a systematic review of existing studies on the topic. Studies were only included if the researchers assessed them as being unbiased, and as providing reliable and robust evidence.

What did the research involve?

This systematic review included 79 randomised controlled trials (RCTs) that lasted for 12 to 14 months and compared taking omega-3 supplements or advice to increase dietary sources of omega-3 fatty acids with usual or lower intake of omega-3.

A meta-analysis was done to determine how effective the different types of omega-3 acids were in reducing:

death from any cause
death from a cardiovascular cause, such as stroke and heart attack
coronary heart disease
stroke
irregular heartbeat

The RCTs included 112,059 adults from mainly high-income countries, but only 25 of the RCTs were considered to be at low risk of bias.

What were the basic results?

Most of the studies assessed increasing omega-3 intake using supplement capsules, but some focused on diet – meaning by comparing an omega-3-rich diet with a standard diet.

The researchers found that increasing omega-3, whether through capsules or an enriched diet, had little or no effect on:

death from any cause (relative risk [RR] 0.98, 95% confidence interval [CI] 0.90 to 1.03 – 92,653 participants)
death from a cardiovascular cause (RR 0.95, 95% CI 0.87 to 1.03 – 67,772 participants)
cardiovascular events (RR 0.99, 95% CI 0.94 to 1.04 – 90,378 participants)
coronary heart disease (RR 0.93, 95% CI 0.79 to 1.09 – 73,491 participants)
stroke (RR 1.06, 95% CI 0.06 to 1.16 – 89,358 participants)
irregular heartbeat (RR 0.97, 95% CI 0.90 to 1.05 – 53,796 participants)

The researchers also found that increasing plant sources of omega-3 in the diet – for example, by eating walnuts or enriched margarine – also made little or no difference to:

death from any cause (RR 1.01, 95% CI 0.84 to 1.20 – 19,327 participants)
death from a cardiovascular cause (RR 0.96, 95% CI 0.74 to 1.25 – 18,619 participants)
coronary heart disease events (RR 1.00, 95% CI 0.80 to 1.22 – 19,061 participants)

How did the researchers interpret the results?

The researchers said the review was the best that has been done to date on the effects of omega-3 fats on cardiovascular health.

It found moderate to high-quality evidence to suggest that increasing plant, fish and supplement-based sources of omega-3 has little or no effect on mortality or cardiovascular health.

They added that previous suggestions that increasing omega-3 is good for you came from trials that have a high risk of bias.

Conclusion

This very large systematic review is probably the best we are going to get in terms of summarising already-published RCTs assessing the effects of increasing omega-3 intake on human cardiovascular health. However, there were still a number of limitations to consider.

The majority of the trials included in the review looked at omega-3 supplements, so it does not really provide reliable information on the benefits of omega-3 obtained from eating fish.

Although diet plays an important role in preventing heart disease, the causes of heart disease are very complex, so it's hard to know whether a "healthy diet" has an indirect effect on heart health. It may be that people who have a healthy diet are also more health-conscious in areas such as alcohol intake, smoking and exercise. Factors such as stress and genetics will also play a role in heart disease.

Finally, the study was carried out in mainly high-income countries, so the findings may not be applicable to lower-income countries, where omega-rich food sources may not be as accessible.

The takeaway message for anyone reading this article is that oily fish remains an important part of a healthy diet. Current recommendations are to have at least 2 portions of fish a week, including 1 of oily fish.