Cancer patients receiving chemotherapy who pop fish oil capsules may be inadvertently reducing their survival odds, according to the results of a new study from the Netherlands.
Researchers at the University Medical Centre in Utrecht found that the popular supplements appear to diminish the effectiveness of anti-cancer medications.
They made the discovery while investigating the tendency of some tumours to become resistant to chemotherapy.
Their work revealed that when some tumours are treated with cancer-fighting drugs, such as cisplatin, they send out chemical signals to stem cells circulating in the blood stream. The stem cells, essentially acting under the direction of the tumours, then produce two specific fatty acids – KHT and 16:4(n-3) – that prevent the medications from working to their fullest potential. In other words, the cancer cells become insensitive to the treatment and the chemotherapy loses its effectiveness.
These chemo-neutralizing fatty acids are also found in commercially produced fish oil supplements that contain omega-3 and omega-6 fatty acids. That fact led the Dutch researchers to suspect fish oil supplements may also interfere with cancer treatments. To test their hypothesis, they gave fish oil to laboratory mice undergoing cancer therapy.
"When we added these products to mice with tumours during chemotherapy, this induced resistance to chemotherapy," research team member Jeanine Roodhart wrote in an e-mail.
The findings, published in the journal Cancer Cell, suggests that fish oil supplements may have an adverse effect on a broad range of chemotherapy medications. Many cancer patients – often without the knowledge of their doctors – take supplements and herbal remedies in the hope of beating the disease.
Dr. Roodhart noted that further studies are still needed to confirm that these particular supplements can undermine cancer therapy in humans – not just rodents. In the meantime, she said, "as a precautionary measure … we currently recommend that these products should not be used whilst people are undergoing chemotherapy."
She added that eating fish is unlikely to pose a problem because they contain much lower levels of the worrisome fatty acids than supplements.