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Q&A with Dr. Alan Kristal about omega-3 fatty acids and prostate cancer risk

July 18, 2013
Dr. Alan Kristal

Dr. Alan Kristal is a member of the Public Health Sciences Division at Fred Hutchinson Cancer Research Center.

Dr. Alan Kristal and colleagues at Fred Hutchinson Cancer Research Center recently published a second large, prospective study in the Journal of the National Cancer Institute that confirmed previous studies linking high blood concentrations of omega-3 fatty acids to an increased risk of prostate cancer.

Their latest findings indicated that high concentrations of EPA, DPA and DHA – the three anti-inflammatory and metabolically related fatty acids derived from fatty fish and fish-oil supplements – are associated with a 71 percent increased risk of high-grade prostate cancer. The increase in risk for high-grade prostate cancer is important because those tumors are more likely to be fatal. Their study also found a 44 percent increase in the risk of low-grade prostate cancer and an overall 43 percent increase in risk for all prostate cancers. Read the news release here.

The study has generated numerous questions, the most common of which Kristal has addressed below.

Should men stop taking fish oil supplements?

Unless your physician has prescribed them for a specific purpose, I would say yes, men should stop using them. The evidence that taking omega-3 supplements prevents cardiovascular disease or diabetes, or is useful in treating diseases such as arthritis, is poor. According to Dr. Mario Kratz, also a nutrition researcher at Fred Hutch, much of this evidence is based on animal models, and these models do not reflect well what occurs in humans. Against such weak evidence for benefit, we now have reasonably consistent evidence that high intakes of omega-3 fatty acids increases prostate cancer risk.

Should men stop eating fatty fish such as salmon?

That is a more difficult question, but I believe the answer is that men can eat fatty fish, in moderation. It is difficult to know from our research how much fish might be “too much.” I think that two servings per week would be reasonable, but more research would be needed to answer this with any certainty.

What about vegetarians who don’t eat fish? If they shouldn’t consume supplements, how can they get essential fatty acids in their diet?

Some of the fatty acids found in flaxseed, walnuts and oils made from soy contain an omega-3 fatty acid called alpha-linolenic acid. It contains 18 carbons, compared to 20 and 22 for the fatty acids found in fish. Humans can convert alpha-linolenic to longer fatty acids, but it is very inefficient and from a practical perspective not important. Vegetarians do tend to have lower levels of long-chain omega-3 fatty acids, but I know of no evidence that this is harmful. The only vegetarian food source of long-chain omega-3 fatty acids I know of is seaweed; supplements derived from algae also provide such fatty acids.

Fish oil capsules

Kristal suggests men stop taking fish oil supplements unless otherwise recommended by a physician in order to reduce their prostate cancer risk.

Did researchers account for pollutants, such as mercury, that could have been inside the fish that study participants consumed?

No, and this is always a possibility. But beyond industrial exposure to cadmium, we have no evidence that pollutants that concentrate in fish affect the risk of prostate cancer.

What is a common-sense approach for men who still want to reap the benefits of omega-3’s but avoid increasing their risk of prostate cancer?

As I noted, the benefits are far from certain. The fatty acids found in fish are required for good health, but in small amounts. A serving or two of fish a week meets my definition of common sense.

Are there any studies that show a correlation between omega-3 levels and women’s cancers?

To my knowledge, this research is inconclusive.

What are the mechanisms behind the association between high levels of fatty acids in the blood and increased risk of prostate cancer?

We have no data on this question and can only speculate. Inflammation, which omega-3 fatty acids tend to decrease, is generally considered something that contributes to cancer, because it stimulates cell growth. However, inflammation is a mechanism the body uses to destroy damaged tissues, which would include a cancer cell. There is probably on optimal balance for inflammation, beyond which too little or too much could be harmful.

Are there other key questions about fatty acids and prostate cancer risk that still need to be answered?

Indeed, the question we need to understand is why. If we understood the mechanism behind the association, we might learn some important facts about prostate cancer biology.

Who funded your research study?

The National Institutes of Health funded this research via the National Cancer Institute and the National Center for Complementary and Alternative Medicine.

Dr. Alan Kristal is associate head of the Cancer Prevention Program and a member of the Public Health Sciences Division at Fred Hutchinson Cancer Research Center.

Updated Aug. 21: Read the full transcript of Dr. Kristal’s interview on the July 19 episode of NPR’s Science Friday or listen to the audio file.



13 Comments leave one →
  1. July 18, 2013 2:43 pm

    Reblogged this on genetics for everyone and commented:
    Many of you have asked about the recent study Hutch study that links consumption of omega-3 fatty acids with prostate cancer. Here I share a really nice post from the Petri Dish blog by the Hutch that answers many questions.

  2. July 19, 2013 11:37 am

    You can listen to Dr. Kristal discuss his study with NPR’s Science Fridays today, July 19, at 12 pm PST here:

  3. July 21, 2013 8:52 am

    What are the mechanisms behind the association between high levels of fatty acids in the blood and increased risk of prostate cancer?
    Dr. Kristal’s answer: “We have no data on this question and can only speculate.”

    My understanding is that these fatty acids are “speculated” to increase prostate tumorigenesis (without any known mechanism) because there was a Selenium/Vitamin E study that also measured the fatty acids and found that the folks with Prostate cancer tended to have higher levels of long-chain ω-3 polyunsaturated fatty acids . Is it possible that there was an inherent inability to best employ these “good” fatty acids? If the study is proven to be more than a coincidence, had the intake of those fatty acids been molecularly distilled (thereby eliminating known toxic contaminates) would results differ?

  4. July 22, 2013 10:13 am

    And the rest of the story…This “fishy” speculation has stirred some pretty compelling responses:

  5. July 22, 2013 10:37 am

    …Any mention about the subjects ratio of Omega 6 to Omega 3?
    “We have to go back in history probably about 80 years when they first did the experiments of taking all fats out of the diets to see what would happen to animals. What happened was pretty striking: they died. They added back certain fats, and then the animals lived. At the time, those fats were called vitamin F. Now we call them essential fatty acids. But there are two groups of essential fatty acids: one group is called omega-6 fatty acids, the other is called omega-3 fatty acids. Now, why is that distinction important? It’s the omega-6 fatty acids that cause inflammation; it’s the omega-3 fatty acids that decrease inflammation. What you have to have is a balance of omega-6 to omega-3 fatty acids. If the balance is too high, we have increased inflammation and that means accelerated heart disease, cancer, and Alzheimer’s. If the ratio is too low, it means our immune system is too depressed and now prone to increased chronic disease because of increased infection”.
    -quoted from Dr. Barry Sears

  6. Patrick Greany permalink
    July 24, 2013 11:52 am

    Everyone interested in this topic should watch the following critical review of this research by Charles Myers, M.D.

  7. July 25, 2013 10:46 am

    Here is a link to Dr. Kristal’s interview with NPR Science Friday in which he answers some of the questions that have been raised about his study:

  8. Andrew Easton permalink
    July 30, 2013 4:16 am

    If the link between fish oil and prostate cancer is so clear and the source is immaterial (either natural or saupplements) then how is it that the South East Asian communities who eat large amounts of fatty fish (as well as other fiish of course) do not have massively increased rates of prostate cancer? In fact they have the lowest rates in the world.

  9. N. Malham permalink
    July 31, 2013 7:34 pm

    I am quite concerned because i have been consuming 10-12 ozs of wild alaskan salmon a week for close to 2 years. Dr. Krystal considers 2 servings of fish a week to be reasonable. How many ozs is a “serving”?

  10. Ted Moore permalink
    August 15, 2013 2:59 pm

    I am currently in a long term study of the effects of daily fish oil vs placebo. Have idea I am on the real stuff. I am seriously considering quitting this study.

  11. Michaela Vidlakova permalink
    October 27, 2013 5:59 am

    Dr.Kristal and others,
    In the connection with omega-3-FA increasing the prostate cancer, did you ever think of measuring the occurence or even the level of lipid peroxides, which are produced if too high amount of PUFA in the organism is present, before all without sufficient levels of all kinds of antioxidants ( vit. E alone is not effective enough!) ? We tried to measure the lipid peroxides in vivo after high supply of PUFA about 40 years ago, unfortunately the methods available by that time were not very helpful, now the spectrum of methods might be much better. It is known, however, that lipid peroxidation is responsible of many disorders, cancer included!

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