Sage Advice Blog

Fish Oil, Chemotherapy, and Metastatic Breast Cancer

December 21, 2017

Alex Speers ND, MS


Within the field of integrative oncology, one of the most common concerns expressed by patients and their oncologists is the potential for interactions between nutritional supplements and chemotherapy drugs. These concerns are typically based on the knowledge that certain supplements and chemotherapy drugs share metabolic pathways. This can be a problem because if a supplement slows down a drug’s metabolism, more of the drug is available, potentially causing more toxicities. Conversely, if a supplement speeds up a drug’s metabolism, less of the drug is available, potentially decreasing its efficacy. While there are certainly times when concerns for supplement-drug interactions are valid, there is also evidence that in some instances, taking specific supplements around chemotherapy may be beneficial.


One example comes from a small 2009 study of 25 women with metastatic breast cancer who were supplemented with docosahexaenoic acid (DHA), a nutrient found in fish oil, while they went through chemotherapy. In the study, the women were treated with a chemotherapy regimen called FEC, which stands for the 3 drugs used (fluorouracil, epirubicin, and cyclophosphamide). The women were instructed to take three capsules of fish oil three times daily, for a total of 1.8 grams of DHA each day. They began taking the fish oil 7-10 days before their first chemotherapy treatment and continued until chemotherapy was finished. As a precaution, fish oil was withheld on the day of chemotherapy.


The researchers then followed the patients and tracked their progress. They found that the median overall survival was 22 months, meaning that half the women lived less than 22 months and half lived more than 22 months. Unfortunately, this finding wasn’t all that encouraging considering that previous research had shown that the median overall survival for women on FEC (without fish oil) was 18-23 months. However, when the researchers split the women into two groups based on their DHA incorporation (how much of the fish oil was taken up by their cells), the women with high DHA incorporation had a median survival of 34 months compared to 18 months for the women with low DHA incorporation. That’s a difference of almost one and a half years, which is significant considering that these were women who had particularly poor prognoses due to most having liver metastasis. In addition, there were no DHA-related side effects observed and no increased toxicity on normal cells from taking fish oil around chemotherapy.


DHA has previously been shown in cell and animal studies to increase the sensitivity of breast cancer cells to anti-cancer drugs, making these drugs more lethal to cancer. It does this by increasing inflammation around cancer cells, which may seem odd considering we typically think of taking fish oil to lower inflammation in the body. What happens is that first, DHA preferentially incorporates into fast-growing cells, like cancer cells. Then, when chemotherapy hits the cells, DHA goes through a process called peroxidation, which results in the production of reactive oxygen species (ROS). ROS cause cell damage and stress out cancer cells, making them more vulnerable to the effects of chemotherapy. Studies have shown that this effect is more dramatic in aggressive cancer cells, which are not able to manage ROS as easily as less aggressive cancer cells.


This study provides early human evidence of a potential survival benefit in taking fish oil around chemotherapy for patients with metastatic breast cancer, likely due to a sensitizing effect on cancer cells. Most importantly, taking fish oil did not cause additional side effects or toxicities to normal cells. The logical next step is to investigate why certain people are better able to incorporate DHA and research strategies to improve DHA incorporation.


Bougnoux P, Hajjaji N, Ferrasson MN, Giraudeau B, Couet C, Le Floch O. Improving outcome of chemotherapy of metastatic breast cancer by docosahexaenoic acid: a phase II trial. Br J Cancer. 2009;101(12):1978-1985.


DISCLAIMER: These statements have not been evaluated by the Food and Drug Administration. There are no financial ties to any supplement companies, pharmaceutical companies, or to any of the products mentioned in this post. This post is not meant to treat, cure, prevent, or diagnose conditions or diseases and is meant for educational purposes. As always, please consult your doctor before trying any new treatments or supplements.

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