The People's Perspective on Medicine

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.)

Flax meal, not flax oil, has lignans which are shown to be protective against hormone-related cancers. If someone were concerned about the supplemental fish oil risk, he could consume dietary omega-3s and add ground flax, if needed. (Omega-3s are also found in walnuts, olives, olive oil, as well as other food sources.)
I also think this study is flawed and that few conclusions can be drawn. I had many of the same questions as others who have commented.
The one thing that seems consistent is that a Mediterranean-type diet and a physically active lifestyle, combined with frequent, satisfying interactions with others produces a healthy and happy individual.

One thing these studies have not included about fish oil and Omega 3 is the people whose diet includes a hearty amount of fish for example in Japan and similar countries. Therefore I would like to know if there are any comparison studies showing any effect on their overall health regarding cancer

The comments are very interesting and I’d like to hear more.

PLoS One. 2013 Apr 17;8(4):e59799. doi: 10.1371/journal.pone.0059799. Print 2013.
Consumption of fish products across the lifespan and prostate cancer risk.
Torfadottir JE, Valdimarsdottir UA, Mucci LA, Kasperzyk JL, Fall K, Tryggvadottir L, Aspelund T, Olafsson O, Harris TB, Jonsson E, Tulinius H, Gudnason V, Adami HO, Stampfer M, Steingrimsdottir L.
Centre of Public Health Sciences, University of Iceland, Reykjavik, Iceland.
To examine whether fish and fish oil consumption across the lifespan is associated with a lower risk of prostate cancer.
The study was nested among 2268 men aged 67-96 years in the AGES-Reykjavik cohort study. In 2002 to 2006, dietary habits were assessed, for early life, midlife and later life using a validated food frequency questionnaire. Participants were followed for prostate cancer diagnosis and mortality through 2009 via linkage to nationwide cancer- and mortality registers. Adjusting for potential confounders, we used regression models to estimate odds ratios (ORs) and hazard ratios (HRs) for prostate cancer according to fish and fish oil consumption.
Among the 2268 men, we ascertained 214 prevalent and 133 incident prostate cancer cases, of which 63 had advanced disease. 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): 0.43 (0.19, 0.95)], no association was found for early life or midlife consumption.
Salted or smoked fish may increase risk of advanced prostate cancer, whereas fish oil consumption may be protective against progression of prostate cancer in elderly men. In a setting with very high fish consumption, no association was found between overall fish consumption in early or midlife and prostate cancer risk.

I have to take drugs that cause my TRIGLYCERIDES to go haywire and the only thing that seems to control that is fish oil. It seems not to be a question of what’s good for me, but what I want to die from. Since I’ve heard that prostate cancer grows extremely slowly, I suppose it’d be wisest to keep taking fish oil pills. Any Help Out There??

This from a physician friend in the nutritional clinical research field:
As you may be aware, an article published in the July 2013 issue of the Journal of the National Cancer Institute suggests there is an association between elevated plasma omega-3 fatty acid levels and a heightened risk of prostate cancer.
This study must be interpreted with a significant degree of caution for a variety of reasons:
The data came from what is referred to as a retrospective, nested, case-control study. The data was extracted from another, much larger, previously conducted trial that was not originally intended to examine the relationship between omega-3 fatty acid levels and prostate cancer. In other words, the original study was not designed to determine any of the conclusions reached in the analysis contained in the article.
The study’s results conflict with the results from other studies that do suggest that omega-3 fatty acids offer a protective benefit against prostate cancer; and these other studies were, in fact, designed to analyze that very outcome. (See link)
Identifying one particular physiologic marker in a group of individuals with a given condition – in this case, an elevated omega-3 level in men with prostate cancer – does not prove causation, especially when that marker can be influenced by diet or behavior and is only measured at a single point in time.
It is also hugely important to realize that the authors of this study did not assess any of the participants’ dietary intake of fatty fish or omega-3 nutritional supplements – the study’s conclusions are based wholly on the results of a single blood test.
The omega-3 index, which measures both EPA and DHA within red blood cells, is a much more accurate indicator of long-term omega-3 intake and tissue status than is the plasma omega-3 level, which is subject to significant day-to-day variability.
A number of confounding risk factors might have influenced the purported outcomes in the study, despite attempts by the investigators to account for them:
53 percent of the subjects with prostate cancer were smokers.
64 percent of the cancer subjects regularly consumed alcohol.
30 percent of the cancer subjects had at least one first-degree relative with prostate cancer.
80 percent of the cancer subjects were overweight or obese.
Considering the extensive body of literature that supports the anti-inflammatory effects of omega-3 fatty acids, there is no credible biological mechanism, nor is one suggested in the article, that would explain why these essential fatty acids might increase tumorigenesis.
Summary: Given the inconsistent data attributable to omega-3 fatty acids and prostate cancer, and acknowledging the broad range of health benefits that are almost universally accorded to omega-3 fatty acid consumption, it would be premature to stop eating fish or to discontinue taking omega-3 nutritional supplements on the basis of this study.

Mayby it’s not Fish Oil itself but is the Mercury and other contaminants causing the Prostate Cancer? I have my husband take 3,000 MG a day and his father and brother have both had Prostate Cancer. Maybe I should not give it to him anymore?
People’s Pharmacy response: Is there a reason you have him taking it? 3,000 mg is a high dose if you are not striving for a particular goal. For general good health, 1,000 mg a day or fish twice a week might suffice.

It is impossible to draw conclusions based solely on terms such as ‘higher’ and ‘lower’. Maybe those of us who take low doses of fish oil have omega 3 levels equal to the ‘lowers’.
Also, it is important to know if the health profiles of the ‘highers’ were the same. Did they all have the same blood work results (lipid profile, etc)?

Do the findings of past studies include cancer-causing agents, not infrequently found in fish taken in both ocean and inland waters?

Have you looked at Dr. Michael Murray’s (naturopathic doctor)website regarding this study
I think, Joe and Terry, you should explore this whole thing with him….I love People’s Pharmacy, have been a fan for years. Thanks for all you do.

Western society teaches us that pills are good. My counsel is contrary to this, I advise against medicine of any sort unless it is known and accepted to alleviate a symptom or syndrome. If your measured level of omega-3-fatty acids falls out of the healthy or normal range, then I would consider supplementation, particularly if some known side effects are present and consistent with that measured level. But consuming omega-3 supplements based upon other criteria (heart, cancer, overall health) is foolish. “If it ain’t broke, don’t fix it.”
For example, if your ascorbic acid level is low and you have symptoms of scurvy, add citrus to your diet or supplement with Vitamin C. But don’t consume Vitamin C for other reasons, particularly if your blood level of ascorbate is normal. Since no symptoms or syndrome is associated with low or high blood levels of omega-3 fatty acids, I would advise against that supplementation under any circumstances. Too many supplementation studies contradict one another, whether they are published, unpublished or about to be published.

It’s important to note, though, that the authors of this study specifically said that Omega 3s from plant sources (flax seed, algae-derived DHA) did NOT have these negative effects on prostate health. These results were for FISH-based Omega 3 only.

Once again we have incomplete or faulty studies or one that does not go into details as to why previous studies were in error. Dr. Sears is a leading expert on Omega 3s and has the following response to this article:
Hopefully this will put this issue to rest.

This study/finding by the same research group irritates me because it goes against common sense! Men eating more omega 3 types of fish are at greater risk of Prostate cancer?! I’m not a doctor but come on! Does that make sense!
Let’s look at the wording, “Conclusions This study confirms previous reports of increased prostate cancer risk among men with high blood concentrations of LCω-3PUFA. ”
OK, “high blood concentrations”. How high, ha? What’s low? And these other men in the studies, what were their levels and other over riding factors? It seems to me that this kind of study (like a lot of these results) is just in its infancy because there are so many other factors that need to be studied in conjunction on these participants.
Now, I buy and take my Dr’s recommended amount of Fish Oil supplement. I also live in the PNW and eat a lot of hatchery raised Chinook and Coho Salmon. Both my Father and Brother have had Prostate cancer surgery! Will I continue taking supplements at the rate recommended by most common doctors? Probably yes. Will I keep eating salmon at the same level? Heck yes, probably more if I can get it!
From Ken, Washington State, USA

I want to know who paid for the study. And how many other studies they paid for whose results they did not allow to be published.

This article and study are pure nonsense! They again show how utterly amateurish the media elites are!
The study is an old, recycled one that was designed to study vitamin E and selenium, not fish oil! They study DID NOT track fish or fish oil consumption! They did not track other dietary fats which also contain omega 3 fats! There is no cause and effect shown, but for the needy people who want attention, it’s perfect for making waves. Bogus and ignorant is the only way to describe this nonsense!

It always amazes me when a new study comes out that goes against all of the studies previously made. I would be more supportive of these results IF they gave reasons why previous studies were in error or were not taken properly. Add to this the relatively small sample size and that there was no supportive data given from millions of men from areas such as in the Far East or Norwegian where fish is a staple and has been for hundreds of years. Certainly these statistics should have come into play when publishing any study of this sort.
We as consumers have gone through these turn-about articles so many times and is not only confusing but raises fears in individuals who have been taking certain vitamins or minerals for long periods of time. It is time for those who conduct these studies to cover all data sources on a particular subject and to go one step further in explaining why previous results were flawed or in error. Anything short of this should be considered as a faulty or incomplete study in my opinion.

Do you think it makes a difference it Omeda-3s were to come from Flax or other veg based consumables?

I’m a vegetarian so I have been taking flax seed oil for omega 3’s. My husband does as well, if they are derived from a plant are the results the same?

How about people in Alaska, especially Eskimos, they eat a lot of fish. Based on this research, they should have higher incidence of prostate cancer? I have a friend, he was diagnosed prostate cancer many years ago, never never ate any fish in his diet….
So many factors play in the development of cancer. In my opinion, this reseach is biased.

I scanned the text of the study report to try and gain some insight into what kind of Vitamin E was used in the trials. I might have missed it, but I didn’t see any reference to what type of Vitamin E was used. It is my understanding that there are four types of Vitamin E, and that if only one type is used (such as alpha tocopherol) exclusively, then this could contribute to the results found, whereas if mixed tocopherols are used, the negative results would be less likely or unlikely. I’m not a physician or nutrition expert, but this would be an important detail.
I’ve been taking fish oil gelcaps twice a day for years, and also consuming trout or sardines at least twice a week for many years. My last PSA test at age 55 showed a 0.4 level. Perhaps there are other factors affecting the study with fish oil. I have avoided consuming any tuna fish for a decade due to concerns about toxins that accumulate as one goes up the food chain. Please keep reporting on this but also delve into the important details that may confound these studies.

I take Flaxseed oil which has Omega 3 in it. My blood work is great. I take 6 1300 capsules daily. My cholesterol is 187, ldl is 132.8, hdl 36, Triglycerides 91. I am 82 and feel great. I am also taking testosterone. My psa is 1.67.

Your Gleason score is not a bad one. I’m sure it will be able to be treated with surgery or radiation easily. Just explore each option including watchful waiting before you do anything.

Wow..I have been taking Lovaza 2 gram am and 2 gram pm for 4 years…I was just informed that I have prostrate cancer. Surgery or radiation has been recommended. I had 3 tubes out of 12 that contained cancer. My gleason score was a 3-4. So I need to have this taken care of. I am 65. No more LOVAZA.
Insurance does not like it anyway since it is very expensive. They ask each time for pre approval. Last night this was on national news. Recommending NO fish oil supplements period..just fish in moderation.

I had a friend who bragged to me that he ate fish every night for a year, and presumably did not stop then. He died in his 40s from esophageal cancer.

Is Fish Oil still OK for women?
People’s Pharmacy response: That depends on what you are using it for. Recent research shows that fish oil has different effects on blood platelets in men and women:
Another recently published study showed no benefit against heart attacks for either men or women:
Some basic science research shows, however, that fish oil inhibits estrogen-fueled breast cancer cells:

The abstract of the Vitamin E study referenced does not identify whether the alpha or gamma version of Vitamin E was studied. Sloppy science. The authors of that study at least comment:
>Potential explanations for the null findings include the agent formulation and dose
Sure wonder who pays for these things.

In 2007 I had prostate cancer I had the prostate removed but since the surgery I have taken fish oil-omega-3 so now what is happening to my body !

What about men who have already been diagnosed with prostate cancer? My husband was diagnosed at age 49 and had a prostatectomy with clear margins. He also has had 2 stents. He is healthy now but takes fish oil supplements and DHA. We also eat fish a couple of times a week. Don’t know what to make of all of this as to what is the best thing for him to do.

Alternative MD, Michael Murray, issued a Special Update e-mail today on this. He reports that this study “used subjects from the much maligned Selenium and Vitamin E Cancer Prevention Trial (SELECT).” Check out his points.
Once again, we can’t trust a study until it’s broken down further by the people we do trust.

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