Objective: Fish intake may reduce the risk of prostate cancer. However, the results of previous prospective cohort studies have been inconsistent, and almost all have been undertaken in Western countries, where total fish intake is low. We therefore investigated the association between fish intake and the risk of prostate cancer in a prospective cohort study in Japan.
Participants and methods: We delivered a self-administered questionnaire including items on dietary intake (40-item food frequency questionnaire [FFQ]), and various lifestyle habits, between October and December 1994 to all male National Health Insurance (NHI) beneficiaries aged 40-79 years in Japan. Usable questionnaires were returned from 24,895 (94%) of the participants. We divided the participants into quartiles based on their self-reported fish intake. We used the Cox proportional hazards model to estimate the hazard ratio (HR) and 95% confidence interval (CI) of prostate cancer incidence according to fish intake, after adjustment for potential confounders.
Results: We identified 95 prostate cancer cases during 7 years of follow-up, to the end of December 2001. An inverse association was observed between fish intake and the risk of prostate cancer. The multivariate HRs (95% CI) of prostate cancer across increasing quartiles of fish intake were 1.00, 0.92 (0.48-1.76), 0.73 (0.42-1.28), and 0.72 (0.40-1.33) (P for trend = 0.23). Among participants aged 40-69 years, the multivariate HRs (95% CI) of prostate cancer across increasing quartiles of fish intake were 1.00, 1.26 (0.51-3.11), 0.86 (0.38-1.94), and 1.01 (0.43-2.34) (P for trend = 0.83). On the other hand, among participants aged 70 years or older, the corresponding multivariate HRs (95% CI) were 1.00, 0.63 (0.23-1.69), 0.60 (0.27-1.30), and 0.44 (0.18-1.11) (P for trend = 0.08).
Conclusions: The risk of prostate cancer tended to decrease among those aged 70 years or older although it was not significant. The relation was not seen in those aged 40-69 years old.