Eating fish rich in omega-3 fatty acids at least once a week was found to reduce the risk by 57%.

High intake of long-chain omega-3 (LC n-3) fatty acids may lower the risk of aggressive prostate cancer, data suggest.

John S. Witte, PhD, professor of epidemiology at the University of California at San Francisco, and colleagues studied 466 men diagnosed with aggressive prostate cancer and 478 controls matched for age and ethnicity. The investigators used a food-frequency  questionnaire to assess diet, particularly with respect to consumption of dark fish (salmon, mackerel, bluefish), which are rich in LC n-3.

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Compared with men who never ate dark fish, those who ate dark fish at least once a week had a 57% reduced risk of aggressive prostate cancer, the researchers reported in Clinical Cancer Research (2009; published online ahead of print).

Patients were considered to have aggressive prostate cancer if they had a Gleason score of 7 or higher, a PSA level above 10 ng/mL at diagnosis, or tumor-node-metastasis stage T2c or higher. 

Dr. Witte’s team also discovered that a particular genetic variant of cyclooxygenase-2 (COX-2) had a profound effect on the association between LC n-3 and aggressive prostate cancer. The presence of this variant in men who had low LC n-3 consumption increased their risk of aggressive prostate cancer more than fivefold. Increasing LC n-3 consumption by 0.5 g/day essentially reversed this positive association, the investigators noted.

COX-2 is the principal enzyme involved in metabolizing fatty acids and it has a key role in chronic inflammation that could lead to prostate carcinogenesis, the authors explained. In addition, COX-2 variants have been linked to prostate cancer.

Dr. Witte’s team concluded that their findings support a hypothesis that LC n-3 consumption may impact prostate inflammation through the COX-2 enzymatic pathway.