Can Fish Oil Cause Prostate Cancer?

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Whenever a newly published health study challenges current thinking, you can bet it won’t be long before the news media starts ratcheting up the drama and jumping to conclusions. This is true of a recent study called “Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial,” published in the July 2013 issue of the Journal of the National Cancer Institute. This study suggests a higher risk of prostate cancer among men who eat omega-3 fatty acids, such as those found in fatty fish like sardines and salmon or in fish oil supplements.

Because I encourage my patients and readers to get plenty of omega-3s, I want to respond to these reports and offer my answer to the question they’ve raised: can fish oil cause prostate cancer? But first, let’s examine the findings.

What the Study Found

The study, which was conducted at the Fred Hutchinson Cancer Research Center in Seattle, WA, claims a link between increased blood levels of omega-3 fatty acids and increased incidence of prostate cancer. The highest blood plasma levels of these polyunsaturated fatty acids, specifically EPA, DHA and DPA, were associated with the highest risk. The research also showed that higher levels of linoleic acid (or omega-6 fatty acids, which most Americans eat too much of) were actually associated with a lowered risk. This would suggest that the more fish or fish oil a man included in his diet, the greater the chances he would develop prostate cancer. It would also mean that increasing his omega-6 fatty acid intake would be a good idea.

So, have I led you astray by telling you to eat your fatty fish and limit your intake of processed vegetable oils that contain omega-6 fatty acids? Should I warn you against taking fish oil and instead tell you to eat more cottonseed and sunflower seed oils? Let’s look at the facts and decide.

A Closer Look at the Study 

This study used what is called a retrospective case controlled cohort design. Simply put, to make their conclusions, researchers from the Fred Hutchinson Cancer Research Center used data from a previous study conducted in 2011 called the SELECT (Selenium and Vitamin E Cancer Prevention Trial). It’s important to note that the original SELECT study did not have the same objective as this current one.  It wasn’t designed to determine whether fish oil led to prostate cancer. The fact that both studies didn’t have the same goal calls into question whether the old data is even relevant to the new study.

What we can be sure of is that association does not prove cause and effect. If this had been an intervention design study, where half the participants got fish oil and half didn’t and they were followed for 20 years to see if they got prostate cancer, then you can say pretty definitively that they are connected. Bottom line, this type of study does not prove cause and effect. If I did a study on sunrise and humans waking up, I would find 100% correlation, but that doesn’t mean that the sun came up because you woke up. Correlation, yes; causation, no.

Another problem with the study is that the researchers did not address whether the men who were studied got their omega-3 fatty acids from eating fatty fish or from taking supplements. Also, there was no regard for their health status before starting the study. Did they start using fish oil as a therapy once diagnosed with prostate cancer or had they been taking it all along?

And what about the myriad other factors that can lead to the onset and progression of cancer, such as how lifestyle affects genetics? Smoking, nutrition, exercise, environmental toxicity, stress: none of these things were taken into account. It is too simplistic to reduce a disease as complex as cancer down to one trigger. In fact, perhaps we should be asking if these men were exposed to toxins and heavy metals from eating mercury-containing fish, which can cause cancer. Or did the men smoke or drink to excess? Was there a history of cancer in the family? What was their personal health history prior to diagnosis? Were they overweight or obese, and did they have other symptoms of diabesity?

Another major flaw with this study’s design involves the way the researchers got their data. They analyzed blood plasma instead of red blood cells. And they did so with one single blood draw! The conclusions would have been stronger and more reliable had they used red blood cell samples, because those provide a more accurate assessment over the long term (plasma tends to provide only a short-term picture). Because the research was based only on samples of a single blood draw, the red blood cell analysis would have given a better picture of long-term omega-3 intake (a couple months of eating salmon, for example, instead of what happens in the body after a single meal). That’s why I suggest people use the omega-3 index test, which measures levels from within the red blood cells.

Consider the Japanese

If it is true that taking fish oil or raising your blood levels of omega-3 phospholipids increases risk for prostate cancer, then why hasn’t this been a problem for Japanese men? They certainly eat their fair share of fatty fish and have done so for generations! The Japanese (and other fish-loving cultures) have been studied many times to test this hypothesis, and guess what? Males in Japan, while having some of the highest levels of EPA and DHA, also have some of the lowest rates of prostate cancer. Only in the most recent studies have Japanese men been shown to have an increase in prostate cancer. Could it be that, as the Japanese begin to abandon their traditional diet of fish, seaweed, and other sea vegetables for the typical SAD (standard American diet, high in saturated fat and linoleic fatty acids), their risk of prostate cancer rises?

It seems that for every claim against fish and fish oil, there are several studies that confirm their benefits. One study, Consumption of Fish Products Across the Lifespan and Prostate Cancer Risk, showed that high blood plasma phospholipids was protective against prostate cancer when fish oil was consumed. Another study showed that omega-3 fatty acids protect against death caused by prostate cancer. And what about the effect of fish oils on the outcome of prostate cancer in men with elevated PSA levels? Again, the literature shows that EPA and DHA have no negative effect.

Personalized Medicine

It’s important to stop and remember that each person has a unique inner ecology and external environment. Contributing factors, such as exposure to environmental toxicity, poor nutrition, and other lifestyle variables, as well as genetics, all play a role in the development of cancer. It’s a complicated disease, and it would be a good idea to pause and look at the whole picture before drawing any major conclusions.

The simple fact is that countless studies have proven the health benefits of eating a diet rich in antioxidants and fiber from fruits and vegetables. And just as we all know that eating your veggies is good for your health, we are now beginning to prove similar health benefits from including healthy fats in your diet. (For more information on how to increase your intake of healthy fats, please see my discussion here). We also know that limiting omega-6 fatty acids and increasing omega-3 fatty acids has been shown to reduce the risk of diabesity in Western cultures.

So, before we toss good medicine aside, we need to examine carefully the factors that contribute to imbalances in the body. We need to assess what we do know and keep asking questions about what we don’t.

We know that a whole foods-based diet, rich in fresh, nutrient-dense fruits and vegetables, healthy fats, and lean protein, does make a positive difference in health outcomes. We know that high-quality, purified fish oils are best. We know that a balanced and varied diet is key for maintaining good health. And we know that moderation is the key to a healthy and sensible relationship to food. Any diet or program promoting an extreme is not realistic, sustainable, or even remotely healthy. Remember, the “dose makes the poison,” so just the right amount—and not too much—will allow you to reap the intended benefits. In the case of fish oil, 1-2 grams daily is appropriate for most people, though some of you may need more. I strongly suggest you work with a trained functional medicine practitioner to help you determine the appropriate doses you need, not only for fish oil but for all supplements. My nutrition coaches are here to help you transform general guidelines into personalized solutions.

So, where do I stand on whether fish oil causes prostate cancer?  I’ll be eating sardines in my salad for lunch tomorrow, and I’ll be taking my daily fish oil supplement with my dinner tonight. And I hope you will be too!

Now, I’d like to hear from you…

Have you been swayed by recent reports to feel that omega-3s can cause prostate cancer?

Will you limit the amount of omega-6 fatty acids you consume?

What are some of your favorite ways to include fatty fish in your diet?

To your good health!
Mark Hyman, MD

18 Responses to Can Fish Oil Cause Prostate Cancer?

  1. Dorrete July 28, 2013 at 6:07 am #

    Thanks for this update Dr Hyman. One really have to understand research and it’s backgrounds to make a inform choice .I will not give up using my omega 3s.

    • N Bagnato July 28, 2013 at 10:34 am #

      Thank you for helping to make the public more research savvy – I have worked in the field of public health for over 20 years and am often dismayed by how research studies and/or data can be very easily misinterpreted. Sometimes research done with good intentions can lead to doing more harm than good once the media gets hold of it. More articles like this one that truly help the lay person understand the implications/validity of the research are sorely needed. Thank you!

  2. charles pavlich July 28, 2013 at 12:26 pm #

    this study may be a sinister evil plot to sell pills so that big evil pharma gets your money. the only bad fish is farmed fish.

  3. Stephen July 28, 2013 at 12:58 pm #

    An excellent analysis of a timely but confusing subject by a capable disinterested third party. These offerings serve the public well.

  4. laura lehrhaupt July 29, 2013 at 7:29 am #

    Thanks for posting. FYI, the original researcher stated in an radio interview, which I posted, that the men were NOT given supplements. The higher levels of Omega 3’s are from diet which led me to ask the same questions. Were their sources of fatty acids contaminated??? Here is the interview: http://www.sciencefriday.com/playlist/#play/segment/9172

  5. Profile photo of Mr. F
    Mr. F July 29, 2013 at 7:56 am #

    Has anyone heard about this/is this correct? – I read an earlier review of this research that pointed out that although there is a statistically significant correlation between higher omega 3s and bad prostate cancer outcomes it is a different issue when the concentrations are looked at. From what I remember that review said that the “high omega 3″ group only had a 5-10% higher blood concentration of omega 3s than the “low omega 3″ group. This difference seems too little to really be meaningful.

  6. Vivian Gregory July 29, 2013 at 2:01 pm #

    Thanks Dr. Hyman for this information, here in Mexico that disinformation was all over the nightly news, and my 85 years old dad was adamant in stopping to take his Omega 3 supplement. I’ll be reading your article to him, hoping he’ll understand it’s in his best interest to keep on taking the Omega 3.

    Thanks for keeping us in well-informed You provide the good information, it’s up to us to follow it!

    Thanks!

  7. Aparna Natarajan July 29, 2013 at 6:00 pm #

    Is it possible that there are higher level of estrogens or more specifically xenoestrogens in the fish consumed, given the high levels of such pollutants in water, that is contributing to the numbers? What about omega3s from plant sources.

    The researcher seemed to be completely against supplements. Wonder why?

  8. Steven M. Hall, MD August 2, 2013 at 1:57 am #

    Mark, you did your usual stellar job of explaining a complex topic. I would also like your thoughts on the topic of researcher personal bias and how that influences his/her conclusions. In my understanding, these particular researchers have a long history of bashing supplements and self-help in general.

  9. Maxie August 4, 2013 at 10:22 pm #

    One problem of these sciences, the remains changing. When science can ever be considered staticly relevant? One time says egg increase cholestrol, 3 years later it says it’s healthy. One website supports drinking coffee each morning, the other says halt coffee. Geocentric and Heliocentric still unproven even with the latest gadgets of NASA. It’s all about faith, without faith no one can live on earth. Do I know Dr. Hymen very well? No. Do I know his past experiences? No. Have I thoroughly checked his degree certificate? Again no. But I have faith in him. Without faith, one has no community. I recommend all of us to join this community and start loathing new ideas of sciences. Cheers!
    Sorry for my english..

  10. Bill September 5, 2013 at 8:43 pm #

    Hi Dr. Hyman,

    I have been following your lectures on PBS and found it quite helpful.

    I am 59 y/o and worked a great deal overseas and I am not living a normal as in having a partner. Some time ago, my PSA levels went up and felt some strange feelings on my prostrate area. Since then, I been listening and paying attention to the reaction of my body.

    I began to eat vegetable drinks and felt improvements on my prostrate and my life is back on track.

  11. Stephen Knows Cancer September 16, 2013 at 4:22 pm #

    While it is great that data from studies are so widely available, this can be one of the drawbacks. This is one of those cases where a sample correlation can get misconstrued as causation. As you mentioned, the Japanese eat more fish than most other nations, but they have long been shown to have low rates of prostate cancer. The Omega 3 fatty acids in fish oil are beneficial for so many reasons (including cholesterol, heart health, and even long-term memory), I just hope that people keep this in mind when they read about this study.

  12. Dr. Karen Krahl, D.C. January 15, 2014 at 11:36 am #

    Another ridiculous interpretation, of poorly collected data, reaching a bizarre if not inaccurate conclusion. Thanks, Dr. Hyman for sorting through the flawed information collection and the poor design. I’ll be taking my fish oil today and having some sardines for lunch. Thanks too for breaking it down, so the general public and your fans become more immune to the media hype, that will probably jump on this and confuse everyone.

  13. Thomas B. Curtis, MD January 16, 2014 at 8:33 am #

    My response, as a believer in Darwinism, is that we can trust there has been selective advantage to eating fish, and flesh eaters may be encouraged to continue fish. There has not been Darwinian influence, as yet, on the eating of packets of fish oil. We have seen that often nutrients work best when combined with their natural partners. In other words, if you can eat carrots instead of taking vitamin A supplements, you’re better off. Here: eating fish is a better strategy than taking fish oil supplements. Also, if we want a better ratio of omega 3/6 fatty acids, perhaps the best thing we can do is stop eating grain fed beef.

  14. Bryce buckland April 1, 2014 at 11:39 pm #

    Very informative, however I would like to see some more meaningful research done on the subject. I race top veteran level mountain bike races. I am now aged 66, am in great shape (same weight as when aged 21) I never smoked, 3 units alcohol per week, no family history of prostate disease and known locally as a very fit athlete for my age.
    I take 500mg odourless garlic and vit c everyday, evening primrose, celenium, zinc and chia. My psa level was fine until 5 years ago after I started on omega three oil capsules 1000mg per day. Since than it has steadily risen from 1.3 until I had a biopsy when it hit 5.1 late last year. this showed cancer and a Gleason score of 5. Still no physical indicators that anything was wrong or even starting to go wrong and even now my GP and surgeon are at a loss to understand why the rapid change. I am now at home recovering after a radical prostatectomy and the Gleason score (since November 2013) had gone on to 8.
    So,this an interesting article for me to read and there’s a couple of points I’d like all men to take on board 1) be sure to get a psa level as well as physical of your prostate (psa may not be accurate in every case, but you need a baseline to work from) 2) some doctors are reluctant to give a psa due it’s sometimes strange readings…remember you are patient so demand it. Good luck to you all.

  15. Charles October 9, 2014 at 9:45 am #

    Very good Dr. Hyman. I have had good results with 2-3 grams per day of omega 3 oils for arthritis pain. I am concerned about the cancer threat. It is very frightening. I had laid off the fish oil for several months and my arthritis has returned in my hands, I have mild pain but it is also demoralizing. Thanks for your help.

    Charles

  16. Nathan November 4, 2014 at 8:39 am #

    Thanks for the informative post. I think more smart, unbiased researched needs to be done to understand cancer and effectively attack it. I am no scientist so I can only do my part and help fund the research. I joined the online movement at http://InternetUsersAgainstCancer.com so I can contribute to research as much as I can.

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