Fish Oil Supplements Could Harm Cancer Patients

Treatment & Doctors

Taking common fish oil supplements or even eating a particular fish may reduce the effectiveness of chemotherapy for cancer patients, including those with malignant mesothelioma, according to a new study.

Doctors and scientists from the Netherlands Cancer Institute in Amsterdam last month found clear, tumor resistance to chemotherapy in pre-clinical models. They determined fish oil can be detrimental.

“We currently advise our [cancer] patients not to take fish oil in the days surrounding chemotherapy treatment,” lead researcher, Dr. Laura van Hussen-Daenen, told “Fish oil supplements might not be harmless [as some believe] during chemotherapy.”

A recent report from the National Institutes of Health shows that fish oil is the third most used dietary supplement in the U.S., after vitamins and minerals.

Fish oil supplements are taken today for a variety of reasons by millions of health conscious people, believing in the low-cost, low-risk benefit from the omega-3 fatty acids. Many cancer patients take fish oil as part of an alternative treatment regimen.

While fish oil might benefit some people in the prevention of some conditions, its higher-than-normal levels of fatty acids could render chemotherapy useless.

Fatty Acids in Fish Oil Spark Resistance to Chemotherapy

The study shows that researchers believe fish oil enables cancer cells to rebound and repair themselves quicker after being hit by the toxic chemicals that normally would have crippled them. In laboratory mice with cancer, even small amounts of fish oil reduced the effectiveness of the chemotherapy.

Based on her observations of the mice, Van Hussen-Daenen said it would be unethical to conduct a clinical trial that administers fish oil to people to see if it made their chemotherapy less effective.

“The major limitation of the current study is the difficulty to directly translate our preclinical data to [actual patients],” the authors wrote. “Our results add to the growing awareness that not all dietary supplements are beneficial or harmless. Some may interfere with the treatment outcome.”

Mackerel and Herring Also May Cause Problems

As part of the research, 30 volunteers without cancer were given either 10 or 50 milliliters of fish oil supplement to measure their rise in a fatty acid known hexadecatrienoic acid. Another 20 volunteers ate mackerel or herring two species of fish known for high fatty acid content and their hexadecatrienoic acid levels rose to similar measurements.

The earlier mice models were given the same levels of the fatty acid and experienced tumor resistance to the chemotherapy.

Researchers believe the membranes of the cancer cells were affected by the fatty acids, making it more difficult for the chemotherapy to enter or making it easier for it to leave.

Cancer Patients Turn to Supplements

As part of the study, 35 percent of the cancer patients who returned their surveys said they were taking a nutritional supplement, and 11 percent specifically said they were taking fish oil.

Patients who receive a cancer diagnosis and are looking for ways to help often begin taking nutritional supplements, yet there is growing concern in the medical community that supplements can interfere with the cancer treatments.

Van Hussen-Daenen stresses the need to discuss any supplements taken during treatment with your doctor.

“Our findings are in line with a growing awareness of the biological activity of various fatty acids and their receptors and raise concern about the simultaneous use of chemotherapy and fish oil,” the researchers wrote.

Study’s Results Are Met with Skepticism

A 2011 study from the University of Alberta in Canada concluded that supplemental fish oil could increase the efficacy of palliative chemotherapy for non-small cell lung cancer patients.

Well-respected epidemiologist Tawee Tanvetyanon, at the Moffitt Cancer Center in Tampa, who also is an associate professor of oncologic sciences and part of the center’s mesothelioma program, said he encourages his cancer patients to eat a nutritional diet that often includes seafood. He did not want the study to discourage the consumption of high protein seafood.

“I don’t think [fish oil] will have any negative impact on a patient’s chemotherapy. If you love to eat fish, you can continue to eat it,” said Tanvetyanon, who read the recent fish oil study. “Just because there is an effect on a mouse model doesn’t mean it will affect a human that way. There is not enough evidence out there right now. And there have been conflicting studies.”

Although not a proponent in fish oil supplements, he would not discourage a patient from taking them during chemotherapy. “If you’ve been taking them a long time, it’s probably okay to continue,” he said.

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