Study linking fish oil supplements and cancer causes consumer fears

Increased risk of prostate cancer associated with omega-3 levels

Health food shops have reported a stream of customers concerned about new research suggesting a link between omega-3 fish oils and prostate cancer.

High levels of the oils in blood samples were linked with a 71 per cent increased risk of developing an aggressive and dangerous form of prostate cancer, according to the research.

Omega-3 products are among the top sellers in health food outlets and are a widely used health supplement, said Odhran Kelly chairman of the Irish Association of Health Stores.. "We certainly have had a lot of customers coming in concerned about it," he said of his shop Nourish in Wicklow Street, Dublin.

Details of the research by scientists at the Fred Hutchinson Cancer Research Centre in Seattle were published this week in the important Journal of the National Cancer Institute. The large study measured blood levels of omega-3 oils in more than 2,100 subjects including 843 men who had been diagnosed with prostate cancer.


Dietary supplements
The researchers only measured omega-3 levels, they did not separate whether they came from eating oily fish – widely accepted by nutritionists as a healthy dietary option – or dietary supplements.

The researchers found that those with high levels had a 71 per cent higher risk of developing an aggressive form of the disease and a 44 per cent increased risk of developing low-grade prostate cancer.

The spread between the highest and lowest levels of omega-3 fatty acids, however, was moderate, akin to eating salmon twice a week according to Prof Alan Kristal, senior author of the paper.

The same research team in Washington state produced a similar study two years ago that showed a link between high levels of omega-3 oils in the blood and the incidence of prostate cancer. The researchers pointed out, however, that their study provided no data about how omega-3 might affect the person’s outcome once diagnosed with prostate cancer.

Omega-3s are found naturally in oily fish and are a very popular health supplement because of their anti-inflammatory properties, said Jill Bell, president of the Health Stores Association. “It is one of the most commonly used supplements.” Studies had also shown benefits in cardiovascular and brain health, she said.

There was no evidence of cause and effect in the US study, she said. “Until there is a bit more evidence to the contrary we can see nothing but benefit from taking omega-3,”.

The Irish Cancer Society offered similar advice.

The Central Statistics Office does not have figures for omega-3 imports or exports as a separate heading as it falls under the general category fish oils.

But consumers in Britain anually spend about €135 million on fish oil supplements.

Worldwide 10 per cent of the retail market for omega-3 products goes into supplements and is valued at €25 billion.

Dick Ahlstrom

Dick Ahlstrom

Dick Ahlstrom, a contributor to The Irish Times, is the newspaper's former Science Editor.