Dietary factors protective against breast cancer in Japanese premenopausal and postmenopausal women

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Abstract
Since components of the Japanese diet that might be responsible for the relatively low breast cancer incidence rates observed in Japan have not been clarified in detail, a case‐referent study with reference to menopausal status was conducted using data from the hospital‐based epidemiologic research program at Aichi Cancer Center (HERPACC). In total, 2,385 breast cancer cases were included, and 19,013 women, confirmed as free of cancer, were recruited as the reference group. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were determined by multiple logistic regression analysis. There were reductions in risk associated with high intake of milk and green–yellow vegetables (green leafy vegetables, carrots and pumpkins) among both pre‐ and postmenopausal women. The protective effects of the Japanese diet were more prominent among postmenopausal than premenopausal women. The adjusted OR of fish consumption (5 or more times per week vs. fewer than 3 times per month) was 0.75 (95% CI 0.57–0.98, ptrend = 0.01) for postmenopausal breast cancer. A significant decrease in postmenopausal breast cancer risk was also observed for increasing intake of fruit (OR = 0.61, 95% CI 0.41–0.91). Thus, traditional Japanese dietary factors may protect against breast cancer development, especially among postmenopausal women.