Earlier this week every major news media was running a report claiming that a recent study proved that high intakes of fish oil supplements caused a 71% increase in prostate cancer. Then they usually brought on their resident MD who confirmed that yes this appeared to be true and they should stop taking all fish oil supplements. The problem is I doubt any of them read the study, they just repeated the headline.
Over the years there have been over 2,000 studies which have looked at fish oil and cancer. Most found that fish oil lowers the risk and death rate for many types of cancer, including prostate. So lets take a closer look at the study and you’ll quickly see how flawed it is and really seems to just an error filled attempt to slander the fish oil supplement industry.
The study they pulled data from was the abandoned SELECT trail that ran between 2001 and 2004 looking at the effects of selenium and Vitamin E on cancer prevention. The study was not designed to look at omega 3 levels, so the study was not looking at fish oil in relation to prostate cancer, but they pulled data from this study anyways.
Here is a summary of the errors they made.
- The participates in the study had their blood lipid (fat) levels checked when they signed up for the study. It was the one and only test the 834 participates had of their blood lipid and omega-3 levels.
- The study included sick and healthy people, but no indication of who may be taking fish oil supplement. It is common to find that when someone becomes ill that then they will start trying different alternative treatments, like fish oil, to help combat their disease.
- Every man in this study already had prostate cancer
- The study jumps to the conclusion that since fish oil supplements are so commonly taken that they could have contributed to the increase, yet no data to support that
- The test only measured the percentage of omega-3 oil compared to total blood lipids. They never looked at the actual amount of omega-3 fats in the blood.
- There were no questions about dietary or supplement use. Nor were there questions of when the last piece of fish was eaten or fish oil, krill oil, or flax seed oil supplement was taken. This makes sense as the original study wasn’t looking at omega-3, but only selenium and vitamin-E
- the difference between the blood levels of omega-3 was only 0.2% between the high and the low. This is statistically an insignificant difference in omega-3 levels. (High was 4.66% vs 4.48% for the low)
- If the findings of the study were true, then you should find epidemic prostate cancer in countries and areas where fatty fish consumption is high like the Scandinavian countries, Japan and much of Asia, but prostrate cancer is low in these areas.
- The statistical model they used (Cox proportional hazards) doesn’t apply to a single measurement vs a later outcome. This statistical model is designed to look at a long term daily use of a drug, food, supplement vs the outcome. Had an appropriate statistical method been used the outcome could have been completely different.
- Even with the statical model they used, the difference between the omega-3 fatty acids was NOT statistically significant.
- The same researcher, Brasky, had another study in 2011 which didn’t show any correlation between omega-3 and prostate cancer.
- They cited another study by Chavarro in 2007 that showed a very strong benefit of fish oil sources of omega-3 in protecting against prostate cancer.
- There was no control group in this study. The original study which was abandoned did have a control group, but none in the data they pulled.
- The overall levels of fish oil found were low, so it’s likely they were NOT supplementing.
- It is known that fat is the fuel of prostate cancer, and since this study was done in the U.K. where a lot of fish and chips are eaten is it possible that the fish oil was coming from fried fish and that those people with prostate cancer had higher fats in their diet and that that was the true link to prostate cancer- but none of this information is available in the study data.
Other factors to consider:
- A recent study my Szymanski in 2010 showed a large reduction in late stage or fatal prostate cancer.
- Several other studies, Lietzman, 2004 and Terry 2001, showed in large populations that increased omega-3 consumption correlated to a reduction in prostate cancer.
- A recent study by Zheng in 2013 looking at over 500,000 participants and 16,000 incidence of breast cancer found that each 0.1g increase in omega-3 daily consumption correlated to a 5% decrease in risk of breast cancer. So the average fish oil supplement is 1,000 mg, or 1.0 g, so that would be a 50% reduction in breast cancer risk.
- The study was funded by the National Cancer Institute. Many will argue this, but the pharmaceutical and health care industry can not afford a cure for cancer. It is a multi billion dollar industry and if cancer were cured think of the drug companies, hospitals, oncologist, etc who would be out of business. So the health care industries and especially the pharmaceutical companies will fund studies which are geared to discredit what does work, but they can’t make money on.
In summary, this study should never have been published and should have been rejected. I suspect though that as quickly and powerfully that it came out in the media that there was a real PR push behind it – Someone wanted to damage the supplement industry and they jumped to the conclusion that fish oil supplements were the cause when the study never even disclosed if a single person even took supplments of any kind, at fatty fish, etc.
Here is the study which is making the headlines http://jnci.oxfordjournals.org/content/early/2013/07/09/jnci.djt174.abstract
Download the full study here Fatty acids and prostate cancer JNCI Brasky July 2013.pdf
Here is a critical critique by a professor of Radiation Oncology department at the Harvard Medical School Click Here