Fish oil and prostate cancer – what’s the real story?

Fish oil and prostate cancer – what’s the real story?

Fish oil and prostate cancer – what’s the real story?

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You can’t help but have noticed the media headlines today claiming that fish oil capsules cause prostate cancer. Now we all know that the media can have a tendency to “exaggerate” the truth in order to write a catchy story but is there any truth to their claims?


Let’s look at the facts:


  1. The study is what’s called an case control study. This means that the researchers simply took a selection of the general population and assessed them. This sort of research can only provide a “correlation” or that two independent events are occurring at the same time. Correlation does not imply causation, or that one event has caused the other. All scientists know this, as do all sensible journalists.


You can think of it this way:


As ice cream sales increase, the rate of drowning deaths increases sharply.

Therefore, ice cream consumption causes drowning.


This is clearly illogical – in this example it is a third event ie summer that links the two – but this is exactly what the media has concluded from the research article.


The study actually reports that men with high levels of omega 3 in their blood also have higher rates of prostate cancer. These are two independently occurring events that are occurring at the same time.


In order to show a cause and effect, the researchers would need to give one group of men fish oil capsules and see if they developed prostate cancer. They haven’t done that so we simply cannot conclude that the two events are linked.


It is possible that prostate cancer is associated with an inability to use omega 3, which is why it remains in the blood stream. Or, even more likely, is that the men with high levels of omega 3 ate more fish, which sadly these days is often contaminated with cancer causing chemicals such as PCBs.



  1. The researchers didn’t even study fish oil capsules! They didn’t even look at the men’s diets. All they did was measure the amount of omega 3 in the blood. Where this came from is anyone’s guess!


  1. Researchers can’t take into account all the different factors – called confounders – that might also influence the development of prostate cancer. Perhaps the men with high levels of omega 3 ate more fish which had been farmed using growth hormones or antibiotics. The amount of confounders which could be influencing these results is simply impossible to measure.



What should you do if you’re now worried about this research? The advice with fish remains the same:

1) Only buy the best quality fish oil capsules that have been cleaned of all the harmful chemicals. You definitely get what you pay for with fish oil so price is a good indicator of quality in this case.

2) Avoid eating big fish such as tuna and swordfish which are higher up the food chain and have higher levels of contaminants and only choose fish from unpolluted waters.

3) Seek the advice of a fully qualified naturopath before using high doses of any supplement.

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