Dietary Diversity Score Associated With a Reduced Risk of Breast Cancer: A Large Population-Based Incident Case-Control Study.

Background: Breast cancer (BC) is responsible for a high proportion of cancer-related morbidity and mortality. A varied diet may play a role in the onset of BC. Objectives: We aimed to investigate the association between dietary diversity and BC risk. Methods: This population-based case-control study was conducted between May 2021 and October 2023, comprising 600 incident BC cases and 600 general population controls. We employed a valid and reliable 168-item food frequency questionnaire, with data collected one year prior to the date of diagnosis for cases and within the past year for controls. A dietary diversity score (DDS), focusing on consuming a variety of 5 food groups, with attainable scores between 0 and 10, was created as an indicator of total nutritional quality. Potential confounders were also assessed, including educational year, menopause, age at menarche, family socioeconomic status during adolescence, multivitamin intake, and benign breast diseases. We employed logistic regression models to estimate crude and adjusted odds ratios (ORs), controlled for potential confounders, to estimate the effect of DDS on BC risk. Results: DDS was associated with BC odds when analyzed as both a continuous and a categorical variable. The OR for DDS as a continuous variable was 0.90 [95% confidence interval (CI): 0.82, 0.99]. For participants with a DDS between 2.5 and 6, the OR was 0.58 (95% CI: 0.36, 0.95), and for those with a DDS >6, the OR was 0.41 (95% CI: 0.23, 0.73). A clear dose-response association was also observed [test for trend: OR= 0.66 (0.49, 0.86)]. Conclusions: We identified DDS, a measure of a balanced diet, as a novel protective factor for BC. Given the global increase in BC morbidity and mortality, this finding underscores the need for public health interventions and educational programs targeting diverse and balanced dietary patterns.