One of my patients asked me about a recent article she read in a magazine that said that fish oil supplement consumption may lead to increased risk of cancer. She has rheumatoid arthritis and is in need of fish oil for help with controlling inflammation in her body.
She showed me the article, and the article plainly stated that studies show fish oil may increase cancer risks by three times the normal risks if you take fish oil regularly. When I read this article, which only had less than five lines in that section about this, it made me concerned about all the other people who may have read the same article and may now be refusing to take fish oil for high triglycerides or for inflammatory diseases like rheumatoid arthritis or lupus -- based on one study where future study results may or may not confirm such a finding, especially since other studies in the past had found opposite results or conflicting results.
So, for the sake of my patient and many more out there like her similarly confused by the fish oil study published in April of 2012 in the Archives of Internal Medicine, let's dive a bit deeper into the specifics of this article and discuss how to use the data to help further our health goals.
In this study, which was geared towards looking at the effect of B-vitamins and fish oil on cardiovascular disease, researchers found ancillary data that suggested increased risk of cancer in women who took fish oil. They saw that this increase was not from B-vitamins but was in the women who took fish oil. This finding was not found in the men of the study. The age group studied was 45 to 80 years old. The dosing of the fish oil was 600mg in a 2:1 ratio of EPA to DHA.
Based on the results at first glance, it is understandable why someone would automatically jump to the idea that this is a definitive concerning study result and that the subjects should stop taking their fish oil. However, even the authors of this article state that this study should be considered preliminary data and that further studies are needed with a study target of studying fish oil and cancer risks in women. Because this study was not originally designed to tease out the cancer risks but rather to explore cardiovascular disease prevention, study results from a study designed specifically for evaluating cancer risks with a large study group would be better suited for re-evaluating these preliminary findings.
Also, there is a question that the findings of fish oil and increased cancer risks were found in a small group of women and that these women are older. Thus, there is some question as to whether age of the women comes into play as far as the increased cancer risk is concerned. In a prior study, post-menopausal women with higher exposure to fish showed positive correlation with increased risk of estrogen-positive breast cancer, so there is concern that extra fish oil may affect hormonal balance in older women as compared to men. However, some of these studies that suggested concern about higher polyunsaturated fat (PUFA) intake with higher risk of cancers in women also had more association with total PUFA intake and to a lesser extent with omega-3 fatty acids.
Interestingly, there are also prior studies that suggest fish oil can significantly improve fatigue in cancer patients. However, there are other studies that suggest fish oil may decrease the effectiveness of some chemotherapy agents as well.
So, all in all, I do believe that there is a lot of confusing data out there about fish oil in regards to cancer, so I am in agreement with the authors in the April article that further studies are needed. However, having said that, there are also higher risks of heart disease and cancers in patients who battle with chronic inflammatory diseases like rheumatoid arthritis or inflammatory bowel diseases. So, the question becomes whether busing fish oil to help decrease inflammation in the body might help more with cancer prevention in these patients than if they were left without the fish oil... or would fish oil help with inflammation, but still the risk of cancer would be high.
Essentially, what we need are further studies in regards to fish oil and cancer to look at specific disease groups most likely to be taking fish oil. In my opinion, if you do not have any diseases -- especially if you do not have an inflammatory disease -- there is no need to be taking fish oil. Get the healthy fats and vitamins and nutrients from a healthy, balanced anti-inflammatory diet instead.
However, if you do have a severe inflammatory disease, it's important that researchers further continue to look at fish oil in regards to using it for helping to treat these diseases, because these diseases naturally put these patients at higher risk for cancer and the question would come down to whether fish oil can help to decrease cancer risks in these patients who are taking it to help treat inflammation.
For now, my recommendation for patients is to take fish oil for the goal of treatments that have been seen in prior studies to help with disease control -- such as hypertriglyceridemia and inflammatory rheumatological diseases. However, if you are healthy and you are taking fish oil for a generic goal of prevention, I would suggest not taking fish oil unnecessarily, but rather getting your nutrients from a healthy diet instead.
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 Valentina AA, et al. B Vitamin and/or ω-3 Fatty Acid Supplementation and CancerAncillary Findings From the Supplementation With Folate, Vitamins B6 and B12, and/or Omega-3 Fatty Acids (SU.FOL.OM3) Randomized Trial. Archives of Internal Medicine. 2012; 172 (7): 540-547.
 Stripp C, Overvad K, Christensen J, et al. Fish intake is positively associated with breast cancer incidence rate. J Nutr. 2003;133(11):3664-3669
 Roodhart JM, et al. Mesenchymal Stem Cells Induce Resistance to Chemotherapy through the Release of Platinum-Induced Fatty Acids. Cancer Cell, 2011; 20 (3): 370 DOI: 10.1016/j.ccr.2011.08.010