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Fish Oil Linked to Prostate Cancer?

Do you ever get the feeling that you are damned if you do and damned if you don’t? That could easily be the conclusion of a new study about omega-3 fatty acids and prostate cancer.

For the last 30 years we have been told to eat more fish to protect our hearts and our brains and improve our overall health. And if we can’t stand fish, we are told to take fish oil capsules.

Now here comes a study published in the prestigious Journal of the National Cancer Institute telling us that men who have higher levels of omega-3 fats circulating in their blood stream are at higher risk (44%) for prostate cancer compared to men with lower levels of such fats. The men with the highest levels of omega-3s were also at greater risk (71%) for aggressive prostate cancer compared to men who had lower levels.

And it’s not just supplements. Eating lots of fatty fish (salmon, tuna, trout, etc) may also pose a problem. The study involved 834 men diagnosed with prostate cancer. They were matched with roughly 1,400 men who did not develop cancer. Levels of omega-3 fats (DHA, EPA, DPA) were measured. Most of the men did not take fish oil supplements, so presumably their levels of omega-3 fats were correlated in large measure with the amount of fish they consumed.

This is not the first time omega-3 fats have been linked to prostate cancer. The same research group picked up a similar signal in 2011. They reported in the American Journal of Epidemiology that men with higher levels of DHA in their blood had significantly more high-grade prostate cancer than men with lower levels of this omega-3 fat.

The lead author, Thomas Brasky, PhD, was quoted:

“What’s important is that we have been able to replicate our findings from 2011 and we have confirmed that marine omega-3 fatty acids play a role in prostate cancer occurrence. It’s important to note, however, that these results do not address the question of whether omega-3s play a detrimental role in prostate cancer prognosis.”

In other words, even though fish oil is associated with a greater risk of being diagnosed with prostate cancer, the researchers don’t yet know whether this means men with high levels of omega-3 fats in their blood will die from prostate cancer faster than other men.


Ok, so that was the official story and what the media picked up on. Let’s dig a bit deeper.

This was NOT a placebo controlled trial that randomly assigned men to fish oil or placebo and tracked them for years. That would be the highest qualilty study and would more reliably answer the question whether fish oil actually caused prostate cancer. This epidemiological study could only detect an association.

The study took one snapshot of omega-3 fats in blood at the enrollment stage and did not determine  blood levels over time. The investigators did not know whether the levels of omega-3 fats in blood were because men were taking fish oil supplements or eating fish. There has been the suggestion that most of the men did not take supplements, so presumably their omega-3 blood levels were due to diet rather than pills. Dietary data was not included in the report, however. It seems counterintuitive that eating fish two or three times a week would increase the risk of prostate cancer. This issue clearly requires much greater investigation before we tell men to stop eating fish.


So, what are we to make of this latest research? First, we can only say that there may be an association between levels of omega-3 fats and prostate cancer but we cannot say eating fish or taking fish oil causes prostate cancer.

We can say that the cardiovascular benefits of fish oil supplements have been disappointing. A large meta-analysis of well-conducted studies in the Journal of the American Medical Association revealed that fish oil supplements did not seem to protect against death from heart attacks. And a large Italian study published in the New England Journal of Medicine on May 9, 2013 also produced disappointing results. Over 12,000 patietns were recruited for this research. They all were at high risk for heart attacks because of previous events or diagnosed heart disease. They were randomized to receive either fish oil supplements (1 gram daily) or placebo. These patients were followed for an average of five years. The fish oil supplements did not reduce death or disease from cardiovascular complications.

One begins to think that a lot of conventional health wisdom is falling by the wayside.

We are not ready to give up on fish, however. We still think that fish is a healthy food choice, but we are beginning to think that vegetarians may be on to something. And if a man is at high risk for developing prostate cancer because of family history or other factors, he might want to cut back on fish oil supplements until we have much better data on this controversial topic.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
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I have been taking phenodiazepams since 1974 to control painful cramps and spasms 2nd to a mid-brain injury and coma following an auto accident. As a result my triglycerides got out of control. My Doc read in a publication from Duke University that fish oil would control this. I am now taking Klonopin 3 times a day and every time I take it I also take at least 2,000 Mg. of fish oil and have been doing so for close to a decade and a half. My triglycerides stay at normal levels and I’ve suffered no ill effects from the fish oil.
If fish or fish oil caused damage, I believe everybody would have heard about it doing so in Japan and China, where fish is a staple food. I think cautions against consuming fish or fish oil are ridiculous and should be removed from this site, as they needlessly frighten people as they did me when I first read them.
The site owners should at least ask Duke Medical school (easy for them to do) how they can tell their graduates to recommend fish oil to their patients if what is posted here has any merit at all.
JB – tutorjb1

Japan and other Asian countries consumes more fish and fish oils than people of the United States and has less incidents of prostate cancer. United States though, consumes more processed foods, meats and junk foods…. Maybe we should investigate this first instead of blaming a substance (fish oil) that has been around longer than the typical american junk food…..

This publication and the associated amplification has distorted the public understanding of the role of omega-3’s from fishoil, which are essential fatty acids required by our body for normal cellular function.
For starters, supplementing fishoil in men with prostate cancer has been shown to reduce mortality.
Japanese have twice the level of omega-3 compared to Americans, yet have 1/8 the rate of prostate cancer.
Cardiovascular mortality has been shown in studies to be inversely related to omega-3 levels.
We now have purified fishoils free of carcinogens and mercury.

I think the most interesting observation is that the men who eventually developed prostate cancer had an average of 4.66 percent fatty acids in their blood. The ones who didn’t get prostate cancer had a 4.48 percent concentration. This is a 0.18% difference and I think that is statistically insignificant. An investigator has to interpret this via “relative risk” to assign any risk at all. Relative risk is a convenient way to lie with statistics. It gets a lot of media attention, but it doesn’t mean anything. The men who developed prostate cancer had about the same level of fatty acids in their blood as those who didn’t.

I take 300 mg fish oil every day. I did a test to see if it lowers cholesterol and it lowered mine quite a bit!! also I am menopausal and have very severe hot flashes. I liked reading your comment about fish oil and Estrogen. Breast cancer or any cancer you develop while taking hormones feeds the cancer so It’s important to see the Dr regularly!! I am also type 2 Diabetic so I am always getting metabolic panels done and regular A1C blood tests. If I am wrong about Estrogen & Cancer then please correct me. It will be a relief for me!!!

Have any studies been done on the effects of fish oil on women? I have an afibrillation diagnosis as well as worsening osteoarthritis and have been told to take fish oil supplements. Perhaps I’m doing myself more harm than good with the fish oil supplements?

I have been eating 1 to2 tuna sandwiches for lunch every school day since the first grade and during the week ever since. Plus salmon twice week most of my adult life.
No cancer and I am 77 years young. Rog.

I have suffered from a pain-causing brain injury for 40 years that has required me to take increasing amounts and strengths of phenodiazepams for foot spasms and cramps in order to walk and have a quality of life that’s not Hell on Earth. A side-effect of the meds has been totally out of whack triglycerides that only at least 6,000 mg. of fish oil geltabs/day has been able to control (Recommended by Duke Med. School).
I was horrified after reading the fish oil/prostate cancer report linked to the story in the most recent People’s Pharmacy bulletin. I didn’t know what I was going to do. It seemed my choices were living in agony without being able to walk or sleep for as long as I could take it, having to deal with prostate cancer or liver disease or jumping off an overpass onto I-40 during rush hour Thanksgiving Day.
Fortunately, there have been several intelligent and apparently informed comments debunking the initial report that I can add to my over 30-years’ problem-free experience taking at least 6,000 mg of fish oli as geltabs/day to eliminate my concern and the doomsday choices above.
Thank you very much. It’s great to be able to read about such initial reports at a site like this with a forum that has intelligent, informed contributors. I am 61, have been using fish oil geltabs daily for 25-30 years and just had excellent blood-work, due in large part to taking the fish oil geltabs (about 6,000 mg/day).
In your case we think fish oil makes total sense, especially since you are under medical supervision. The risk, if it exists at all (remember this was an epidemiological study and NOT a gold-standard randomized controlled trial), is probably fairly low. In your situation the benefits probably far outweigh the risks.

Fantastic report!
One correction: the lead author’s name is Theodore, or Ted, not Thomas. (He’s my brother.)

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