Fish Oil Leads to Prostate Cancer?

Something new to worry about.  Prostate cancer and fish oil.  Will these doctors ever get it right?

A new study has shown that too much fish oil (and fish) could lead to prostate cancer.  Say what?  Writes David L. Katz, MD, MPH, director of Yale University's Prevention Research Center, this recent headline caught his attention: "Fish oils may raise prostate cancer risks, study confirms."

Katz neither confirms nor denies the possibility that the study may be correct.  Instead, he reports, "The study does not prove that fish oil intake causes prostate cancer. But nor is the study dismissible rubbish, as the large crowd of fish oil proponents gathered around it with harpoons in hand would like to contend."

There were some steps taken that aren't usually in a study like this, and some that were.  "Blood was obtained from men at baseline as they enrolled into the study," he relates.

Over time, more than 800 men developed prostate cancer, which, as I heard somewhere, all men develop if they live to a certain age, before they die (and not usually of prostate cancer). According to Katz, the researchers matched these men on the basis of age and race to others in the study who had not developed prostate cancer, and compared those baseline blood samples for various things, including fatty acids (or omega-3 levels).

The results? Even the researchers could not believe it.  But higher omega-3 levels were seen in the men with prostate cancer than in those without. Omega-3 fat is fish oil.

Because he was unsettled by this, Katz continued exploring and found that Japanese men, whose diet is high in omega-3 fats, had much lower rates of prostate cancer, so felt somewhat reassured.  But then he went on to find that Japanese men who ate more than the average amount of fish had a higher rate of prostate cancer.

Scandinavian men, who also eat a high amount of omega-3 fats, have relatively high rates of prostate cancer, too, Katz discovered.

To further confuse the issue, Katz writes, "And finally, there’s the Inuit, who consume omega-3 marine oils at legendary levels. Prostate cancer is rare among them, even when it is sought at autopsy, and omega-3s have been invoked as a potential explanation why."

There were some factors in the study that were not brought out, such as the fact that the men who went on to have cancer already had higher prostate-specific antigen (PSA) levels when their baseline blood was originally taken, and some even had a family history of prostate cancer.  So these men might have gone on to develop cancer, no matter what.

But here's where it gets murky, Katz points out.  "As the authors note, this is not the first study to show an association between higher omega-3 levels and prostate cancer," he writes. "And in population studies around the world, higher intake of fish and higher rates of prostate cancer have run together."

So, what's the deal?  Katz says you can't ignore the fact that some studies have shown definite links between omega-3 fats and prostate cancer.  But where is it coming from?  Carcinogens in the fish itself?  A rogue cell escaping the body's immune system fine-tuned by omega-3 to suppress inflammation (inflammation has been shown to lead to cancer)? Could that anti-inflammatory effect unintentionally turn these rogue cells on, into self-propagating ones?

"An attenuation of that immune system vigilance in the form of an anti-inflammatory effect could, conceivably, help give cancer the upper hand," Katz notes.

His advice?  Eat foods rich in omega-3 fats (salmon, almonds, yogurt, eggs), but don't overdo it.  Even take a fish oil vitamin.  It's safe.  Thankfully, my husband's not a big fish eater, but he does take an omega-3 vitamin.  Just follow the old rule.  Moderation, in everything.


  1. There are many ways to skew information to discredit supplements. Here's one: we don't know what terrible condition the subjects were in in the first place. Maybe they were about to die and selected to prove their point. We don't see the actual study to evaluate it for ourselves.

    -Jame from NYC Personal Trainers


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