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Does fish oil really increase prostate cancer risk? A breakdown of the details…

Dr Tasreen Alibhai, ND

A recent study published in the July 2013 issue of the Journal of the National Cancer Institute has led to a media hype and has led to great concerns over the use of fish oil supplements and even eating fish.

The headlines from many news and media reports read:

Taking omega-3 fish oil supplements may increase the risk of aggressive prostate cancer by 70%. Researchers warn against omega-3 pills, and recommend eating just one or two meals of oily fish per week.

Since the release of this study I have received a flood of phone calls and emails with concerns of eating fish oil or taking fish oil supplements. My patients are asking "should I stop taking my fish oil?" My answer is No! There are many well documented health benefits of fish oil. In my opinion one cannot draw such a conclusion from this one study that fish oil increases your risk of developing prostate cancer by 71%.

In any study it is important to understand the details of the study. Was the study designed to find cause and effect? What variables were controlled or considered? What methods of measurements were used to reach the conclusion? Let’s look at some of the details of the study and why I feel no conclusions can be drawn from this study:

fish oil
  1. This study was an observational study. The data was collected from a previous study called the SELECT trial that investigated the effects of selenium and Vitamin E in prostate cancer. An observational study is not designed to find cause and effect. A randomized controlled trial is designed in such a way to find cause and effect.

  2. This study consisted of 2 groups of men. One group did not have cancer. The other group did have cancer. Omega 3 levels were then measured in both groups. The blood levels in the non-cancer group were 4.48%. The blood levels in the cancer group were 4.66%. That is only a difference of 0.2%. I read the study and I am still not clear how that translates to a 71% increase risk in prostate cancer. You can read the details of the study at http://robbwolf.com/wp/wp-content/uploads/2013/07/plasma-FAs-and-prostate-cancer2.pdf

  3. The Omega 3 levels were measured in both groups by single blood test. This type of plasma blood test has great variability day to day. It can change depending on what was eaten that day. If a person took a fish oil supplement that day, the plasma levels can be drastically elevated. The researchers also could not distinguish if the elevated levels were due to eating fish or taking a supplement. An omega-3 index, which measures the levels in the serum, is better test for long term omega 3 levels.

    One great 7 year study from the University of Iceland (April 2013) tracked 2268 men and their intake of fish early life, midlife and later life and their risk of prostate cancer. They found “High fish consumption in early- and midlife was not associated with overall or advanced prostate cancer. High intake of salted or smoked fish was associated with a 2-fold increased risk of advanced prostate cancer both in early life (95% CI: 1.08, 3.62) and in later life (95% CI: 1.04, 5.00). Men consuming fish oil in later life had a lower risk of advanced prostate cancer [HR (95%CI): http://www.ncbi.nlm.nih.gov/pubmed/23613715

  4. All the researchers found is higher levels of omega 3’s in people with prostate cancer. This does not prove that fish oil supplements cause prostate cancer. Many people who are diagnosed with cancer increase their intake of fish oil or eating fish because they are trying to eat healthy. There are a number of studies that show fish oil actually reduces your risk of cancer and can help you live longer if you have cancer.
    1. http://www.ncbi.nlm.nih.gov/pubmed/16123006 Dietary fatty acids and colorectal and prostate cancers. July 2005
    2. http://www.ncbi.nlm.nih.gov/pubmed/23613715 Consumption of fish products across the lifespan and prostate cancer risk. April 2013
    3. A study based from the University of San Francisco found the intake of omega 3 EFA’s strongly associated with a decreased risk of aggressive prostate cancer (63%) if they had a gene known to increase the risk of prostate cancer. In this case the EFA’s were protective if the gene was present.
      Fradet, V., et al. Dietary omega-3 fatty acids, cycloocygenase-2 genetic variation, and aggressive prostate cancer risk. Clinical Cancer Research 2009; 15:2559.
    4. Researchers from Harvard School of Public Health conducted a study of over 20,000 men. They found the men who had prostate cancer and ate fish 5 times a week had a 48% lower risk fo dying from prostate cancer.
      Chavarro J. E. et al. A 22-y prospective study of fish intake in relation to prostate cancer incidence and mortality. Am J Clin Nutr 2008 Nov; 88(5): 1297-303.
    5. The researchers from the SELECT study took into account certain variables such as age, history of diabetes and family history of prostate cancer. Variables that were not taken into account include:
      • 53% of the subjects with prostate cancer were smokers
      • 64% of the cancer subjects drank alcohol regularly
      • 80% were overweight or obese

So what conclusions can be drawn from this study? I say nothing. There may be some relationship between fish oil and cancer; we don’t know what it is. This study doesn’t prove that fish oil increases your risk of prostate cancer by 71%.

I think this study reminds us to educate ourselves, read the research ourselves before jumping to big conclusions. Does this one study mean we should just forget about all the other research that shows the protective properties of fish oil? Or that the lowest rates of prostate cancer can be found in people from SE Asia and Japan who consume high amounts of fish? Read between the lines, look at multiple studies and don’t base your conclusions on one study.

I continue to use fish oil myself and recommend fish oil to my patients. There are many health benefits to eating fish (preferably avoiding fish high in mercury) and taking a fish oil supplement daily (clean of all toxins).

Yours in Health,

Dr Tasreen Alibhai, ND
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