The Physics Police

The Physics Police

Monday, July 15, 2013

Fish Oil

Good news, everyone! I've got some terrible science to share with you. This study was published online last week by the Journal of the National Cancer Institute:
Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial
The study concludes that:
The consistency of these findings suggests that these fatty acids are involved in prostate tumorigenesis. Recommendations to increase LCω-3PUFA intake should consider its potential risks.
The conclusion means to scare people away from taking supplemental fish oils, rich in omega-3 fatty acids, by saying it causes prostate cancer.

This is a grand overstatement of their results, and almost certainly untrue.

First of all, data used are from a case-cohort study. That means, measurements of blood serum levels were taken only once per participant. It is impossible to establish causality in such a study.

If omega-3 fatty acids actually cause prostate cancer, we would expect a dose-response. But:
... there was no dose response.
Which means their conclusion is wrong. Omega-3 fats don't cause cancer. That's just silly.

Then why is there more omega-3 fat in the blood of men with prostate cancer?

Well, as it turns out, many people diagnosed with prostate cancer take fish oil supplements, because they are said to have cancer-protective properties. Fish oil as a cure-all may be cliche, but people still quaff the stuff when they are diagnosed.

In other words, prostate cancer causes a higher omega-3 levels, not the other way around!

Still, in the news, you get headlines like:
Study confirms link between ... omega-3 fatty acids and ... aggressive prostate cancer
Whenever a study is reported to confirm a "link" between two things, my hobby is to assume causality going the opposite direction as implied. That's my right as a vehement skeptic. Though, sometimes, I just yell, "correlation is does not equal causation!" over and over...

So, I've seen a complaint in response to this story which is common in the health news section:
but I thought omega-3 was good for you?
There is a tendency, with regards to health science in particular, for laypeople to engage in black and white thinking. The media will oversimplify things like omega-3 fats, coffee, or vitamins as being either good or bad, and not always consistently. The resulting contradiction is upsetting to those black-and-white-thinking laypersons.

My advice to those laypersons is to stop considering yourself a layperson! Anyone with a High School education is (theoretically) equipped to navigate the world of science. All you need is a healthy skepticism, and a motivation to be informed.

Granted, it takes a whole lot of time and effort to stay informed. (This is the story of my life.)

My goal with this blog is to demystify, debunk (when necessary), and inform. Hopefully, too, this blog will save you, the not-so-layperson, a bit of time. Maybe, also, a whole lot of effort.

Special thanks to Kurtis Frank over at Examine blog for his informative post on this topic.

Another, more detailed summary can be found here and here.

No comments:

Post a Comment