Today

British health experts have cast doubt on whether omega-3 fats can actually reduce the risk of cardiovascular disease.

Consumption of long chain omega-3 fatty acids, found in oily fish such as mackerel, and a shorter chain omega-3, found in some plant oils, is thought to protect against heart disease and cancer.

UK guidelines encourage the general public to eat more oily fish, and higher amounts are advised after a heart attack.

University of East Anglia researchers analysed 89 studies to assess the health effects of long and short chain omega-3 fats on total mortality, cardiovascular events, cancer and strokes.

Each study involved a treatment group and a control group and investigated the effect of omega-3 intake on health for at least six months. Differences in study quality were taken into account to identify and minimise bias.

Pooling the results showed no strong evidence that omega-3 fats have an effect on total mortality or combined cardiovascular events. The few studies at low risk of bias were more consistent, but they also showed no effect of omega-3 on total mortality or cardiovascular events.

When data on long chain omega-3 fats were analysed separately, total mortality and cardiovascular events were not reduced. No study showed increased risk of cancer or stroke with higher intake of omega-3, but there were too few events to rule out important effects.

Lee Hooper, University of East Anglia: "UK guidelines advising people to eat more oily fish should continue at present but the evidence should be reviewed regularly."

Previous studies have suggested that omega-3 fats have protective effects against cancer and heart disease.

But the researchers believe that this trial "has changed the overall picture".

The researchers cannot say exactly why the results of this trial differ from previous studies.

They therefore conclude that it is not clear whether long chain or short chain omega-3 fats reduce or increase total mortality, cardiovascular events, cancer, or strokes.

"UK guidelines advising people to eat more oily fish should continue at present but the evidence should be reviewed regularly," said lead researcher Lee Hooper.

"However, it is probably not appropriate to recommend a high intake of omega-3 fats for people who have angina but have not had a heart attack.

"To understand the effects of omega-3 fats on health, we need more high quality randomised controlled trials of long duration that also report the associated harms."

"We are faced with a paradox," added Eric Brunner, of University College London Medical School.

"Health recommendations advise increased consumption of oily fish and fish oils.

"However, industrial fishing has depleted the world's fish stocks by some 90 per cent since 1950, and rising fish prices reduce affordability particularly for people with low incomes.

"Global production trends suggest that, although fish farming is expanding rapidly, we probably do not have a sustainable supply of long chain omega-3 fats."

The study is published in the British Medical Journal.