BOSTON, MASSACHUSETTS. Epidemiological studies investigating a possible association between fish consumption and prostate cancer have produced inconclusive results. Some have found that an increased intake of fish may help reduce the risk of prostate cancer, but other studies have found no such effect. There is, however, fairly conclusive evidence that, while an increased fish intake (particularly from oily fish) may not prevent the cancer, it does reduce its growth and aggressiveness.
Researchers at the Harvard Medical School now report the results of a large study aimed at determining the association between fish intake and prostate cancer incidence and mortality. The study involved over 22,000 male physicians (ages 40 to 84 years) who were enrolled in 1983 and, at that time, completed a detailed food frequency questionnaire. During an average 19 years of follow-up, 2161 (0.6%/year) of the men were diagnosed with prostate cancer (biopsy-confirmed) and 230 (1.1% of all participants or 0.06%/person-year) died from the disease. Fish intake was positively associated with the intake of tomato products and alcohol, the use of multivitamins and vitamin E supplements, and vigorous physical activity and was inversely related to the intake of whole milk and meats. Most cases (71.6%) were diagnosed when still localized.
The Harvard researchers found no statistically significant association between fish intake and the diagnosis of prostate cancer, and conclude that a high fish intake does not protect against the initial development of the cancer. However, there was a clear correlation between increased survival and fish intake, particularly from oily fish, with men eating fish 5 or more times weekly having half the risk of dying from prostate cancer when compared to men eating fish less than once a week.
The researchers suggest that a high fish intake may delay tumor progression. They also point to a recent study that found men who had undergone a radical prostatectomy for clinically localized cancer were less likely to experience biochemical recurrence if their non-cancerous prostate tissue had a higher level of long-chain n-3 fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). They also point to laboratory data suggesting that EPA suppresses the proliferation of several prostate cancer cell lines. Their final conclusion was that fish intake is not associated with the risk of developing prostate cancer, but a high intake (especially oily fish) does reduce the mortality among men already diagnosed with the disease.
Chavarro, JE, et al. A 22-year prospective study of fish intake in relation to prostate cancer incidence and mortality. American Journal of Clinical Nutrition, Vol. 88, 2008, pp. 1297-303