Something fishy with fish oil?

Several patients have commented/questioned recent news blurbs about fish oil causing prostate cancer. The article from which news sources developed  alarming headlines comes from the SELECT trial investigators. In that trial, 35,000 men over age 50-55, with PSA <4.0, and normal DRE were randomized to receive vitamin E, Selenium, both, or placebo. The results, in spite of earlier evidence for protection, did not find any protective value in the supplements.

That fact in itself should be a cautionary note in considering what supplements do and don’t do. I, myself, took selenium for a number of years based on what I thought was pretty good evidence that it might prevent prostate cancer. In the study I was relying on, patients with a history of skin cancer took selenium to see if they could prevent further skin cancers from developing. A secondary endpoint in the trial was the evaluation of other cancers, and sure enough, there was “statistically significant” less prostate cancer in men who took selenium compared to placebo. That gave rise to the proper, prospective SELECT trial which was negative. However in the article, a secondary endpoint, the rate of prostate cancer as related to long chain omega 3 fatty acid levels in serum, was evaluated. The conclusion was as follows:

“This study confirms previous reports of increased prostate cancer risk among men with high blood concentrations of LCω-3PUFA.”

Now we have the fish oil story. How can you evaluate trials like this that hit the news all the time? First, you might ask yourself how many patients were in the trial. For example, I blogged about Pomi-T earlier this summer. You can look at that blog and find that it was a very small study AND that there might have been a commercial bent to it’s analysis and presentation. I hope my blog was sufficiently cautionary – although I have suggested a few patients might try it if they want, after reading the blog. The SELECT trial passes muster with a large number of patients.

Second, it can be worthwhile to look at other articles on the same subject. My favorite way to do this is via Google Scholar. Open Google and look at “other” in the pulldown menu and you will find it – you can bookmark that or go there via this link and save the bookmark. Enter “fish oil prostate cancer” and you will find a large number of previous trials to go through. Add the word “meta” and you can find some additional articles, like this one. The conclusion seems at odds with the fish oil hype of the media last month:

“Our analyses provide no strong evidence of a protective association of fish consumption with prostate cancer incidence but showed a significant 63% reduction in prostate cancer–specific mortality.”

So my bottom line is that if you simply read the headlines, you are often misled. The real story seems more complex. I continue to recommend reducing fat intake in patients who have metastatic prostate cancer and are watching their psa. I have previously blogged on this topic here. And as for the fish oil story, maybe it could help your heart, (see this reference for the controversies there…obtained by entering “fish oil cardiac meta” at Google Scholar – then restricting to articles since 2012) but I’d say the jury is still out as regards prostate cancer. And whatever YOU decide, be aware of the media’s tendency to hype the latest finding and tell a simplified story.


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8 responses to “Something fishy with fish oil?

  1. Joe Blue

    What a great service you do in pointing us to the information, helping us search, providing perspective, and letting us decide. Superb!

    My pal’s cardiologist recommended replacing red meat with white meat, even pork. Is there any significant evidence on whether pork is better than beef for PC management? Or are they simply both best avoided? Or don’t we know?

    Many thanks again.

  2. Perhaps the greatest criticism of this study is how participants were accessed for ‘fish oil intake.’ No information was collected as to whether they took fish oil supplements or how often they ate fish. Rather the participants were assessed by a single serum phospholipid level test at the start of the study. While this test does measure fish oil consumption, it is greatly affected by consumption over the past 24 hours. So participants were really divided along the lines of “Did you eat fish yesterday?” That strikes me to be too open to confounding influences.
    Fish consumptions impact on health isn’t black and white. Look as Belin’s data on fish and heart disease: it looks like it takes five servings a week to lower heart disease by 30% or one serving of fried fish to increase risk by 50%.
    Fish is complicated and drawing conclusions from this SELECT data is difficult. Better to stick with the meta-analysis from last year.

  3. Don Welker

    Mike; Do you mind if I send your “blog” comments to my Cancer Group? Don

  4. Pingback: PCPT rides again – finasteride (proscar) to the rescue? | prost8blog

  5. Jeff Frey

    Dr. Glode.
    It looks like there was criticism of the Brasky, et al 2013 paper that you quoted. See Brenna, et al March 2014 in “RE: Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial”, JNCI: Journal of the National Cancer Institute, Volume 106, Issue 4, 1 April 2014, dju015,
    Brenna says the Brasky study “uses inappropriate measures of dietary exposure to omega-3 fatty acids, which show very low consumption levels overall.” He states: “The Brasky et al. study ( 1 ) reported levels of long-chain omega-3s that are in a very narrow range as follows: the no cancer group had mean levels of 4.48%, the low-grade cancer group had mean values of 4.66%, and the high-grade cancer group had levels of 4.71%. By way of comparison, vegetarians who consume no long-chain omega-3 have plasma PL long-chain omega-3 levels of 4.1% ( 3 ), and subjects fed a fish-rich diet for 2 weeks had plasma PL levels of 21.5%.”
    Nevertheless I have stopped taking fish oil tablets as I am undergoing RT for the next 7 weeks.
    Thanks for your prost8blog–there is tons of good information here.

  6. Jeff, you have done everything I could hope from after writing the original post. Namely, you looked up some of the basic literature (rather than just accepting some headline) and reached a conclusion/approach that you feel makes sense for you. Nice job! As you know, the supplement literature is pretty messy…

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