Fish Oil Reduces Chemotherapy Effectiveness

Pile of Herring Fish

Eating fish like these herring can elevate fatty acid levels in the blood for hours.

Fish oil supplements have gained popularity for their many health benefits, but there is a new warning about their possible consequences. Researchers were surprised to find that fish oils in the body can interfere with chemotherapy treatments, making the treatments less effective.

Dr. Emilie Voest and team, working out of the Netherlands Cancer Institute in Amsterdam, published their study Thursday in JAMA Oncology. In 2011, they were surprised to see that fatty acids in mice neutralized chemotherapy drugs, and they became concerned about whether the same thing would happen in human cancer patients.

The study involved feeding commercial fish oil supplements to mice as well as human volunteers. Even at low doses, at two teaspoons of Omega-3 fatty acids for humans, the blood of the mice and humans showed elevated fatty acids in their blood hours later. The researchers also analyzed people who ate fatty fish, with mackerel and herring contributing the most to fatty acid levels in the blood and salmon and tuna having less of an effect. This demonstrates that when someone consumes supplements or fatty fish, the fatty acids can circulate throughout the body for long periods of time.

The researchers then treated some of the mice who had tumors with chemotherapy. They found that the fatty acids from the supplements suppressed the chemotherapy drugs, cutting their ability to fight tumors in half. They did not repeat the same test on human chemotherapy patients for ethical reasons. Although the research shows the effect of fish oil on chemotherapy in mice, not humans, the evidence is convincing that real chemotherapy patients would have the same experience.

The researchers caution that fish oil may not have the same effect on all chemotherapy treatments or all tumors. Every cancer case responds a little differently to the same treatment. In addition, the effect was studied for cytotoxic chemotherapy agents, which fight cancer by damaging the DNA of tumor cells, and may not affect more targeted chemotherapy agents. Critics also argue that the study did not determine whether humans metabolized fatty acids the same was as mice when undergoing chemotherapy.

Currently, some cancer websites recommend patients take fish oil supplements to help ease the side effects of chemotherapy. It turns out there may be some truth to that, as the fish oils reduce the chemotherapy’s effectiveness and the side effects at the same time. The researchers say that as a precaution, chemotherapy patients should actually avoid taking fish oil supplements or consuming fish from the day before to the day after a treatment so that their chemotherapy has maximum effect. When the researchers surveyed a group of cancer patients, about thirty percent said they took supplements, with about eleven percent saying they were taking Omega-3 fatty acid supplements along with their chemotherapy.

The researchers plan to further study the effects of fatty acids on chemotherapy. The research will include looking at a compound that inhibits fatty acid effects, determining if it helps chemotherapy patients who take fatty acid supplements.

Omega-3 fatty acids are often praised for their ability to reduce the risk of cardiovascular disease, improve eye health, and help brain and nerve development. Some people believe the supplements could help children with autism and ADHD as well as benefit adults with mental health disorders, although these benefits are not currently supported by strong scientific evidence. Fatty acids come from fish oil supplements as well as from consuming fish, calamari, eggs, meat, and plant based foods like flax seed and tree nuts.

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