About 19 million American adults consume dietary fish oil supplements.

These supplements, which primarily consist of the omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid, are widely used as a remedy for chronic diseases.

However, the effects of EPA and DHA supplementation on cancer risk have been inconsistent.

In a study, a team of researchers from the University of Michigan and University of Texas MD Anderson Cancer Centre have shown that the gene 15-lipoxygenase-1, or ALOX15, is essential for helping EPA and DHA suppress colorectal cancer.

The results, published in Cellular and Molecular Gastroenterology and Hepatology, emphasise the need to screen for the presence of ALOX15 in cancer patients when developing prevention strategies using EPA and DHA supplements.

Large clinical studies focusing on the association between fish oil, EPA, DHA and cancer have largely been inconclusive.

While some have shown that these supplements can reduce cancer risk, others have shown no benefit or even an increase in cancer incidence.

In the current study, researchers first compared the response of mice given a diet supplemented with fish oil to a control diet.

To their surprise, fish oil increased the number of colon tumours in mice exposed to chemicals that cause inflammation and accelerated colon tumour formation.

When DHA and EPA are consumed, they are broken down into molecules called resolvins that prevent chronic inflammation, a key feature in cancer formation.

This metabolism of DHA and EPA depends on the enzyme ALOX15, which is usually turned off in various cancers.

The team tested whether mice lacking ALOX15 responded differently to fish oil supplements compared to control mice.

They found that the loss of ALOX15 increased colorectal tumours when the mice were fed fish oil, although the degree differed based on the type of omega-3 acid.

There were fewer tumours in mice that were fed EPA diets compared to DHA.

The commonly used forms of EPA and DHA include free fatty acids, ethyl esters and triglycerides.

Lovaza, which contains the ethyl ester forms of EPA and DHA, is approved by the Food and Drug Administration to treat high levels of triglycerides in the blood.

Overall, Lovaza and the ethyl ester and free forms of EPA reduced the tumour numbers and volumes, especially when the mice contained ALOX15.

On the other hand, the different variants of DHA were unable to inhibit tumour development in mice lacking ALOX15.

The presence of ALOX15, however, reduced tumour growth.

“Not all fish oil supplements are the same,” said Imad Shureiqi, professor of internal medicine at the University of Michigan and a member of Rogel Cancer Centre.

“It is also important to ask whether the person who is taking the supplement has the required enzymes to metabolise these products to prevent chronic inflammation and subsequently cancer development.”

Although the reported results were from studies mostly done on animals, the findings suggest that having colon polyps without ALOX15 will make EPA and DHA less effective in stopping tumour growth.

Shureiqi recommends that people talk to their physicians before they take fish oil supplements.

The team is now working on developing drugs that can help increase ALOX15 expression in cancer cells.

They hope that by doing so, these new drugs will aid the supplementation of EPA and DHA for preventing colon cancer development.

Source: Michigan Medicine - University of Michigan