Japanese Dietary Pattern and All-Cause and Cardiovascular Disease Mortality Across Diverse Topographical Settings: The Japan Collaborative Cohort Study

OBJECTIVE: We examined whether the association between adherence to the Japanese dietary pattern and all-cause and cardiovascular disease (CVD) mortality is consistent across diverse residential topographical settings in Japan. METHODS: This prospective cohort study included 48 479 adults aged 40-79 years from the Japan Collaborative Cohort Study, with baseline dietary assessment in 1988-1990. Adherence was quantified by the Japanese Diet Index 8 (JDI-8), with components dichotomized at sex-specific medians. Residential municipalities were classified as coastal, urban inland, flat/intermediate inland, or mountainous inland. Shared frailty Cox proportional hazards models with a municipality-level random intercept (33 municipalities) estimated hazard ratios (HRs) and 95% confidence intervals (CIs). We tested effect modification by residential area using interaction tests and stratified analyses. RESULTS: During a median follow-up of 19.2 years, 9304 all-cause deaths and 2685 CVD deaths occurred. Comparing the highest with the lowest JDI-8 quartile, HRs were 0.929 (95% CI, 0.872-0.990; p for trend = 0.034) for all-cause mortality and 0.862 (95% CI, 0.766-0.970; p for trend = 0.023) for CVD mortality. Interactions by residential area were not statistically significant (p for interaction = 0.246 for all-cause and 0.185 for CVD mortality). Component-level distributions varied by area, with urban inland residents having lower proportions of miso soup, rice, and fish intake. CONCLUSIONS: Higher adherence to the Japanese dietary pattern was associated with lower all-cause and CVD mortality, with directionally consistent associations across diverse residential settings. The absence of significant heterogeneity supports generalizability within Japan, although stratified estimates are exploratory.