The health benefits of oily fish have been advocated for 20 years. Adding one or two servings a week of mackerel or salmon to the household shopping list is believed to help fend off heart disease and has been claimed to ease the symptoms of asthma and bowel disease, prevent premature birth, boost memory, and cure depression.
Now US researchers say that taking fish oil supplements may cut the risk of breast cancer. Previous dietary studies have been inconsistent, possibly because few people meet the recommended target for oily fish consumption. Taking supplements could result in higher levels of the omega-3 fatty acids that bring the benefit, they say.
Among 35,000 middle-aged women who took the supplements regularly over six years the incidence of breast cancer was reduced by almost a third (32 per cent), the researchers found.
The results, published in the journal Cancer Epidemiology, are likely to further boost the booming market for the supplements, worth about US$2bn (NZ$2.8bn) globally in 2007, doubling since 2003.
Euromonitor, which published the figures, predicted fish oil sales would reach US$2.5bn by 2012.
The omega-3 fatty acids in fish oils - eicosapentaenoic acid (EHA) and docosahexaenoic acid (DHA) - reduce inflammation which is a fundamental cause of disease. Claims for their health benefits have proliferated over the last two decades.
The most contentious area has been over their role in brain development. Omega-3 fatty acids are crucial to the growing brain and growing numbers of parents have been giving their children supplements in the hope it will boost their intelligence and powers of concentration.
In 2006, Lord Winston, the TV presenter and fertility pioneer, fronted advertisements in the UK for St Ivel Advance, supplemented with omega-3 which was marketed as "clever milk".
Other scientists have been critical of the claims and studies at the University of Teesside in 2006 and the London School of Hygiene and Tropical Medicine in 2010 found no evidence of benefit on cognitive function in the general population or older people.
Emily White, of the Fred Hutchinson Cancer Centre in Seattle, Washington, who led the latest study showing a protective effect against cancer, said: "It may be that the amount of omega-3 fatty acids in fish oil supplements are higher than most people would typically get from their diet."
However, she warned that the findings were preliminary.
"Without confirming studies specifically addressing this we should not draw any conclusions about a causal relationship."
A spokesperson for the UK Food Standards Agency said yesterday: "We recommend eating two portions of fish per week including one of oily fish, which has been shown to help protect against cardiovascular disease. There isn't enough evidence at the moment to draw any firm conclusions about other health benefits, for example in relation to cancer or cognitive function."