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Experimental studies suggest that marine fatty acids have an antitumor effect on prostate tumor cells. The aim of this study was to investigate whether high consumption of fish and marine fatty acids reduces the risk of prostate cancer in humans. We followed 47882 men participating in the Health Professionals Follow-up Study. Dietary intake was assessed in 1986, 1990, and 1994, using a validated food frequency questionnaire. During 12 years of follow-up, 2482 cases of prostate cancer were diagnosed, of which 617 were diagnosed as advanced prostate cancer including 278 metastatic prostate cancers. Eating fish more than three times per week was associated with a reduced risk of prostate cancer, and the strongest association was for metastatic cancer (multivariate relative risk, 0.56; 95% confidence interval, 0.37-0.86, compared with infrequent consumption, i.e., less than twice per month). Intake of marine fatty acids from food showed a similar but weaker association. Each additional daily intake of 0.5 g of marine fatty acid from food was associated with a 24% decreased risk of metastatic cancer. We found that men with high consumption of fish had a lower risk of prostate cancer, especially for metastatic cancer. Marine fatty acids may account for part of the effect, but other factors in fish may also play a role.

The aim of this study was to evaluate loss of information from a reduced food frequency questionnaire as compared with an extensive reference method developed to assess the intake of heterocyclic amines (HCAs). Food frequency data were linked to concentrations of HCAs in cooked foods to estimate the individual daily exposure to a combination of five HCAs. The number of food items in the questionnaire was reduced and selected in three ways: (a) according to the contribution to the estimated total intake; (b) the between-person variance; or (c) dishes included in other studies. The effect on sensitivity, specificity, concordance, the correlation coefficient, kappa, and simulated relative risks was determined using information from a population-based study conducted in Stockholm. Only a limited amount of misclassification was introduced when the number of dishes was reduced from 39 to 15 or 20, and no major difference was seen when dishes were selected according to the total intake or the between-person variance. Our data indicate that for a specific exposure, such as HCAs, the loss of accuracy in an analytical epidemiological study is small and may not be relevant when the number of dishes in a food frequency questionnaire is decreased, if the initially chosen dishes are carefully selected and cover a reasonable part of the total intake or between-person variance.