July 10, 2013
Omega 3 Fatty Acids Boost Prostate Cancer Risk

While a diet high in omega 3 fatty acids probably delivers some health benefits omega 3s also boost prostate cancer risk.

SEATTLE A second large, prospective study by scientists at Fred Hutchinson Cancer Research Center has confirmed the link between high blood concentrations of omega-3 fatty acids and an increased risk of prostate cancer.

Published July 11 in the online edition of the Journal of the National Cancer Institute, the latest findings indicate 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 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.

The increase in risk for high-grade prostate cancer is important because those tumors are more likely to be fatal.

The findings confirm a 2011 study published by the same Fred Hutch scientific team that reported a similar link between high blood concentrations of DHA and a more than doubling of the risk for developing high-grade prostate cancer. The latest study also confirms results from a large European study.


The scientists can only speculate about causal mechanism.

One potentially harmful effect of omega-3 fatty acids is their conversion into compounds that can cause damage to cells and DNA, and their role in immunosuppression. Whether these effects impact cancer risk is not known.

Would immunosuppression boost risk of other cancers as well? Or is prostate cancer better suppressed by the immune system than other types of cancer?

We need cures for cancer. Every day our cells get mutated and every day any one of us could get a mutation that kicks off cancer progression.

Share |      Randall Parker, 2013 July 10 10:15 PM 

lhf said at July 11, 2013 6:56 AM:

Is prostate cancer higher among populations that eat a lot of oily fish?

Scott said at July 11, 2013 3:27 PM:

I looked at the World Cancer Research Fund International Site. It looks like Northern Europe is scattered in the following places on the Prostate Cancer List. #5 Iceland, #8 Norway, #14 Sweden and #19 Finland. It also looks like the Caribbean is represented by at least 6 of the top 20. The US was rated as #18.

It looks like this determination could be based on some other factor that was not mentioned in what I saw.

DdR said at July 12, 2013 6:32 AM:

"71 percent increased risk of high-grade prostate cancer"

What are we talking about in absolute terms? In other words, I could say that, instead of 1.7 out of 10,000 (0.017%) being inflicted with high-grade prostate cancer, 2.9 out of 10,000 (0.029%) men now are who had consumed Omega 3 fatty acids. This is a significant increase in relative terms, but in absolute terms, only one additional male is affected by fish-oil supplementation out of a male population of 10,000 souls. I'd take this risk if my chances of heart disease and other inflammatory diseases are significantly reduced, wouldn't you?

I'm always skeptical of these studies when they only cite relative changes and not absolute. My guess is that less that the number of actual individuals who are deletriously affected by Omega 3 supplementation is low.

Where's the critical analysis, Randall?

Tim Hogan said at July 12, 2013 7:40 AM:

The Great Fish Oil Experiment

I am not a Ray Peat torchbearer but there is really no better medical advice contrarianism on the market. http://raypeat.com/articles/articles/fishoil.shtml

One of the keys to taking maximum advantage of fish oil is to also include other anti-inflammatories to make sure that this polyunsaturated fatty acid does not rancidize once taken.

philw1776 said at July 13, 2013 8:12 AM:

Given that Asians like the Japanese who eat lots of fish consuming fish oils have very LOW incidence of prostate cancer I don't believe this study. Conversely could there be some genetic immunity factor in Asians?

dbfair said at July 13, 2013 10:08 AM:

The study's authors indicate that they did not differentiate between high blood concentrations of omega-3 fatty acids due to fish consumption vs fish oil supplement consumption. They also speculated that omega-3 supplement use is low compared to fish consumption, implying that the major cause of high blood concentrations of omega-3 fatty acids in their study is consumption of fish, not supplements. Could carcinogenic contaminants in fish (mercury, PCBs, etc.) be the primary driver of increased prostate cancer risk? Perhaps fish oil supplements are safer?

Wolf-Dog said at July 13, 2013 5:44 PM:

philw1776 wrote:
"Given that Asians like the Japanese who eat lots of fish consuming fish oils have very LOW incidence of prostate cancer I don't believe this study. Conversely could there be some genetic immunity factor in Asians?"

This is an excellent point because if the fish oil "supplements" used in the clinical study consist of rancid fish oil tablets, this would be significantly different from eating fish that is relatively fresh, even frozen fish.

The fact that the Japanese people eat a lot of fish, comparable to those who take a lot of fish oil tablets, seems to disprove that clinical study, unless, of course the Japanese are genetically different from Europeans in this area.

Wolf-Dog said at July 17, 2013 11:22 AM:

Here is the summary of a Japanese clinical study that seems to indicate that fish oil prevents prostate cancer, at least in the environment in Japan (their genetics and/or their fish might be different.)


A case-control study of diet and prostate cancer in Japan: possible protective effect of traditional Japanese diet.
Sonoda T, Nagata Y, Mori M, Miyanaga N, Takashima N, Okumura K, Goto K, Naito S, Fujimoto K, Hirao Y, Takahashi A, Tsukamoto T, Fujioka T, Akaza H.
Department of Public Health, Sapporo Medical University School of Medicine, South 1 West 17, Chuo-ku, Sapporo, Hokkaido 060-8556, Japan. tsonoda@sapmed.ac.jp
The age-adjusted incidence of prostate cancer is low in Japan, and it has been suggested that the traditional Japanese diet, which includes many soy products, plays a preventive role against prostate cancer. We performed a case-control study on dietary factors and prostate cancer in order to assess the hypothesis that the traditional Japanese diet reduces the risk of prostate cancer. Four geographical areas (Ibaraki, Fukuoka, Nara, and Hokkaido) of Japan were selected for the survey. Average daily intake of food from 5 years before the diagnosis was measured by means of a semi-quantitative food frequency questionnaire. We studied 140 cases and 140 individually age ( +/- 5 years)-matched hospital controls for analysis. Estimates of age-adjusted odds ratios (ORs) and linear trends were calculated by conditional logistic regression models with adjustment for cigarette smoking and total energy intake as confounding factors. Consumption of fish, all soybean products, tofu (bean curds), and natto (fermented soybeans) was associated with decreased risk. ORs of the fourth vs. first quartile and 95% confidence intervals (95%CIs) were 0.45 (0.20-1.02) for fish, 0.53 (0.24-1.14) for all soybean products, 0.47 (0.20-1.08) for tofu, and 0.25 (0.05-1.24) for natto. Consumption of fish and natto showed significantly decreasing linear trends for risk (P

Anonymous said at July 17, 2013 12:32 PM:

I think we may have all forgot here that increasing vitamin K2 from foods or supplements have a reduced chance for prostate cancer -- might be way natto is so protective (as with the estrogen like compounds).

Wolf-Dog said at July 17, 2013 1:25 PM:

According to this article fish oil tablets contain very high levels of the cancer-causing chemicals called PCBs:


And PCBs are implicated in prostate cancer:


dbfair said at July 20, 2013 9:59 PM:

Wolf-Dog, thanks for posting that mercurynews article - very interesting. I follow advice to take fish oil supplements instead of eating fish in an attempt to gain benefits from omega-3's without exposure to PCBs, mercury, etc.:


so this is unhappy news. I want to make two points, though:

(1) In the Fred Hutch study which correlated increased prostate cancer risk with high blood concentrations of omega-3 fatty acids, the researchers believe that high omega-3 was *not* due to fish oil supplementation, but rather due to fish consumption:


So although the presence of contaminants in fish-oil supplements is alarming, it doesn't appear to explain the increased prostate cancer risk reported in the study.

(2) Supplements, including fish-oil, can be verified for potency and safety by an independent nonprofit verifier, USP ( www.usp.org ). I recently switched to fish oil products that have the USP seal, and am hopeful that that justifies extra confidence on my part that the product is safe. I noted that fish oil products certified by USP do not appear to be among the 10 products cited in the mercurynews article. I did see that two Nature Made products were cited as dangerous, and although USP has certified some Nature Made fish oil products, they did not certify the dangerous two (cod liver oil and odorless fish oil).

I don't know what to make of the fact that the Japanese study you referenced seems to show fish consumption as protective against prostate cancer, while the Fred Hutch study seems to show the opposite. Without further information, though, my plan was to assume contaminants in fish explain the results of the Fred Hutch study, and hope that clean fish oil supplements provide the best approach to omega-3 health benefits while minimizing cancer risk.

PS I also freeze my fish oil supplements until use to reduce the chance that they will go rancid.

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