Fish oil supplements may raise colon cancer risk in some people, study finds

Fish oil supplements may increase colon cancer risk in some people

Nearly 19 million American adults take fish oil supplements, hoping their omega-3 fatty acids will reduce inflammation and chronic disease risk. A new study suggests these popular pills could actually increase the risk of colorectal cancer in some individuals, depending on their genetics.

Researchers from the University of Michigan and the University of Texas MD Anderson Cancer Center published their findings in Cellular and Molecular Gastroenterology and Hepatology. They identified a specific gene as the crucial factor determining whether omega-3s help or harm.

The crucial role of the ALOX15 gene

The study found that a gene called 15-lipoxygenase-1 (ALOX15) dictates how the body processes omega-3s from fish oil. Normally, the enzyme this gene produces converts fatty acids like EPA and DHA into inflammation-resolving compounds called resolvins.

However, ALOX15 is often deactivated in several cancer types. In experiments with mice, fish oil increased the number of colon tumors in animals exposed to cancer-triggering chemicals. The negative effect was most pronounced in mice that lacked a functioning ALOX15 gene.

Not all fish oil is created equal

The research revealed significant differences between the two main omega-3s. Mice fed diets rich in EPA (eicosapentaenoic acid) developed fewer tumors than those given DHA (docosahexaenoic acid).

The study also tested different chemical forms of these supplements. Several EPA-based treatments showed protective effects in mice with active ALOX15.

• The prescription drug Lovaza (containing EPA and DHA ethyl esters) reduced tumor number and size.
• Ethyl ester and free fatty acid forms of EPA also suppressed tumor growth.
• DHA variants did not prevent tumors in mice lacking the ALOX15 enzyme.

A personalized approach to prevention

The findings suggest a one-size-fits-all approach to fish oil supplementation is flawed. "Not all fish oil supplements are the same," said lead researcher Imad Shureiqi, a professor at the University of Michigan Rogel Cancer Center.

He emphasized the importance of an individual's biology. "It is also important to ask whether the person who is taking the supplement has the required enzymes to metabolize these products." The study implies people with colon polyps who lack active ALOX15 may get no protective benefit—and could even be at higher risk.

Next steps for research and patients

While most data comes from animal studies, the implications for humans are direct. The team suggests testing cancer patients for ALOX15 could be vital when considering omega-3-based prevention strategies.

Shureiqi advises patients to consult their doctors before starting fish oil supplements. Meanwhile, his team is developing medications designed to boost ALOX15 levels in cancer cells.

The goal is to enhance the body's ability to process EPA and DHA correctly, potentially turning a risky supplement into a reliable tool for colon cancer prevention.