Fish Oil Does What?! Oh, Wait…

“My phone has been ringing off the hook. My email in-box
is full. It seems that everyone wants to know if the
headlines about omega-3 fatty acids and prostate cancer
are true.

In case you have just got back from a vacation on
some deserted island with no newspapers and no
internet, let me bring you up to date. The headlines
are saying things like "Fish Oils May Increase Your
Risk of Prostate Cancer” and “Latest Study Links Fish
Oils to Prostate Cancer”.

Once again, it seems like just when you’ve figured out
which foods are good for you, someone tells you
they could actually kill you. It’s no wonder so many of
you have been asking me to cut through the hype and put
this latest study in perspective.

As usual, let me start with the study itself (Brasky et
al., Journal of the National Cancer Institute, doi:
10.1093/jnci/djt174). On the surface, it appears to be
a reasonably well designed study, and the conclusions
were dramatic. They reported that subjects with high
levels of omega-3 fatty acids in their blood were 43%
more likely to develop prostate cancer, 44% more likely
to develop low grade prostate cancer, and 71% more
likely to develop high grade prostate cancer compared
to those with low levels of omega-3 fatty acids in
their blood.

Case closed, you might be tempted to say. However, once
you dig a little deeper, the study does have two
important weaknesses.

1) It used data from another study that was designed
for a totally different purpose. They went back and
analyzed blood samples from a previous study that was
actually designed to measure the association between
vitamin E and selenium intake and prostate cancer.
That’s a scientific no-no.  Let me explain why.

If they had designed a study to investigate the
association between omega-3 fatty acids and prostate
cancer, they probably would have selected participants
with a wide range of omega-3 fatty acids in their blood
at the beginning of the study. The subjects in this
study actually had a very narrow range of omega-3 fatty
acids in their bloodstream.

They also would probably have done a diet analysis and
found out whether the subject’s omega-3 fatty acids
were coming from fish or fish oil supplements. They
might have even asked whether the omega-3 fatty acids
were from farm-raised fish or inexpensive fish oil
supplements known to be contaminated with PCBs. This
study collected none of these data.

2) This is a single study, and individual studies often
provide misleading results. For example, if you examine
their data closely, it looks like heavy drinkers and
smokers might have a decreased risk of prostate cancer.
I think that’s unlikely, but weird associations like
that often pop up in individual studies.

That’s why expert scientists aren’t swayed by
individual studies. We prefer to look at the “big
picture” that emerges when you combine the results of
many studies. For example, a meta-analysis of 24
studies with 461,402 subjects (Symanski et al, American
Journal of Clinical Nutrition, 92: 1223-1233, 2010)
found no association between fish consumption and
prostate cancer risk.

Individual studies ranged from a 61% decrease in risk
to a 77% increase in risk, but the overall effect was
zero! Even more importantly, fish consumption decreased
prostate cancer deaths by 63%.

So what is the bottom line for you?

1) Don’t panic. Don’t change what you are doing based
on the latest sensational headlines. This study has
been way overblown. We have come to expect sensational
headlines and hype from journalists and bloggers
because that’s how they get people to read what they

However, I find the comment from the senior author that,
 ‘We’ve shown once again that use of nutritional
supplements may be harmful’, to be very irresponsible,
especially since they have no data showing that anyone
in their study actually used fish oil supplements.

2) The authors make a big deal out of the fact that
this study replicates the results they obtained in a
previous study (Brasky et al, British American Journal
of Epidemiology, 173: 1429-1439, 2011). However, they
neglect to mention that 4 previous studies showed
decreased risk, and the totality of all published
studies shows no effect of fish or fish oil on prostate
cancer risk (Symanski et al, American Journal of
Clinical Nutrition, 92: 1223-1233, 2010).

3) The benefits of assuring optimal omega-3 fatty acid
intake clearly overshadow the risks. Omega-3 fatty
acids have been shown to lower triglycerides and blood
pressure, reduce inflammation and depression, and may
even help prevent dementia.

4) This study does raise a caution flag, but I would
not recommend reducing your omega-3 fatty acid intake
on the basis of these data alone – especially since
most published studies show no increased risk of
prostate cancer. There are much better designed studies
underway that should clearly show an increase in
prostate cancer risk if it is a real effect. I will
monitor those studies closely and keep you abreast of
any new developments.

To Your Health!
Dr. Stephen G. Chaney"

(Professor of Biochemistry & Medical Biophysics & Nutrition at the University of North Carolina at Chapel Hill Medical School.
Dr. Stephen Chaney has published 97 papers and 12 reviews in peer-reviewed scientific journals on nutrition for a leading biochemistry textbook.
Dr. Chaney also runs Chaney Lab at UNC, a top Cancer research lab.)

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