Fish May Protect Against Prostate Cancer

Men who routinely have fish on their plates may reduce their risk for prostate cancer, finds a study published in the June, 2001 issue of Lancet.

Researchers at the Karolinska Institute in Stockholm, Sweeden analyzed data on 6,272 Swedish men whose lifestyle habits, including diet, smoking, and exercise frequency, were tracked from 1967 to 1997. During those three decades, 466 men were diagnosed with prostate cancer and 340 died. However, men who ate no fish showed a double to triple higher risk of prostate cancer than men who ate moderate or abundant amounts of fish.

What do fish carry that could be so important to humans? Study author Paul Terry and colleagues say it's omega 3 fatty acid, a type of fish oil already shown to have multiple biochemical effects in human health, including lowering cholesterol. Now, scientists ask whether it can block tumor development. Other studies have even indicated enough omega 3 in the diet can protect against depression.

Fish high in omega 3 include salmon, herring, and mackerel, all common foods in the typical Swedish diet, researchers point out. Other kinds of fish that do not have high levels of omega 3, researchers add, would unlikely have an effect on prostate cancer risk. Fish may not just help protect against some types of cancers, but may assist protecting our body from disease in general.

"Since few dietary and other modifiable factors seem to be associated with lower risk of prostate cancer, our results may indicate an important means by which this disease might be prevented." Essential fatty acids in fish inhibit the growth of prostate cancer cells in the lab dish and in experimental animals. Earlier studies have found that higher the concentration of fatty acids in a man's bloodstream, the lower his risk of prostate cancer.

But studies of fish consumption and prostate cancer based on large populations are scarce, the authors state. "Furthermore, such studies often measure only a small variation in fish consumption and lack controls for confounding variables. Finally, the type of fish studied is often not described."

"Only fish high in omega-3 fatty acids are likely to lower the risk of prostate cancer." People in Sweden traditionally eat a lot of fatty fish from Northern (cold) waters, such as salmon, herring, and mackerel, which contain high amounts of omega-3 fatty acids, the authors say.

"Our results support the hypothesis that fatty fish consumption lowers the risk of prostate cancer, possibly through inhibition of arachidonic acid-derived eicosanoid biosynthesis, the authors say. Results of a cross-sectional study in 16 regions of Europe "showed greatly increased (three-fold to four-fold) plasma concentrations of eicosapentaenoic acid (EPA) in people from Sweden and Denmark who consumed high amounts of fatty fish."

EPA competes with arachidonic acid as a substrate for cyclo-oxygenases. High concentrations of EPA can lead to important changes in relative concentrations of tumor growth enhancing prostaglandins.

References:

Terry P, Lichtenstein P, Feychting M, et al.: Fatty fish consumption and risk of prostate cancer. Lancet. 2001 June 2;357(9270):1764-66. [http://www.thelancet.com/journal/vol357/iss9270/full/llan.357.9270.original_research.16461.1] Registration may be required, but this article is FREE).

Key concepts: Fish oil, omega-3 fatty acids, alzheimer's, dementia