A longitudinal association between the traditional Japanese diet score and incidence and mortality of breast cancer—an ecological study

Background The traditional Japanese diet is considered one of the important factors of health and longevity in Japanese people. Breast cancer is the most common cancer among women in the world. However, the association between the traditional Japanese diet and breast cancer is unclear. The purpose of this study was to investigate the longitudinal association between the traditional Japanese diet score (TJDS) with the incidence and mortality of breast cancer in an ecological study. Methods Food supply and breast cancer incidence and mortality by country were obtained from an international database. TJDS by country was calculated from nine food groups and the total score ranged from −9 to 9, with higher scores indicating greater adherence to a traditional Japanese diet. Longitudinal associations of interaction between TJDS and fiscal year on breast cancer incidence and mortality were investigated in 139 countries with populations of 1 million or greater. The longitudinal analysis was evaluated using four linear mixed-effect models with different adjustment covariables. Results Many countries with high scores on TJDS had lower distributions of breast cancer incidence and mortality in 1990–2017. Longitudinal analysis using a linear mixed-effect model controlled for socio-economic and lifestyle covariables showed that the interaction between TJDS and fiscal year was significantly associated with incidence of breast cancer (−0.453 ± 0.138, p