Diet Quality Scores Inversely Associated with Postmenopausal Breast Cancer Risk Are Not Associated with Premenopausal Breast Cancer Risk in the California Teachers Study

Background: Evidence for the association between diet and breast cancer risk is inconsistent Thus, research that compares indexes of overall diet quality may provide new insight. Objective: We examined the association between diet quality indexes and pre- and postmenopausal breast cancer risk in a large prospective cohort. Methods: This was a prospective analysis of 96,959 women, aged 22-104 y, in the California Teachers Study cohort (1995-2011). Diet quality was characterized by 4 different indexes. Specifically, we examined Alternate Mediterranean Diet (aMED), Alternative Healthy Eating Index-2010 (AHEI-2010), Dietary Approaches to Stop Hypertension (DASH), and Paleolithic index (PALEO) scores with the risk of developing breast cancer. We used multivariable Cox proportional hazards regression models to derive HRs and 95% CIs for breast cancer risk. Results: In the analysis of 42,517 women at risk of premenopausal breast cancer, there was no association between any of the indexes and incident breast cancer (346 cases). In the analysis of 54,442 women at risk of postmenopausal breast cancer at baseline, higher AHEI-2010, aMED, and DASH scores were inversely associated with incident breast cancer (3523 incident cases). Respectively, HRs (95% CIs) comparing quintile 5 to quintile 1 (reference) for AHEI-2010, aMED, and DASH indexes were 0.87 (0.78, 0.97; P-trend = 0.004), 0.91 (0.82, 1.02; P-trend = 0.03), and 0.89 (0.80, 1.00; P-trend = 0.03). The PALEO score was not associated with postmenopausal breast cancer (HR for quintile 5 compared with quintile 1: 1.05; 95% CI: 0.94, 1.17). Conclusions: Diet quality indexes that emphasize intake of whole grains, vegetables, fruits, legumes, and nuts and seeds and de-emphasize red and processed meats and sugar-sweetened beverages were modestly associated with a lower risk of incident postmenopausal breast cancer risk. However, they were not associated with premenopausal breast cancer, and the PALEO score was not associated with cancer risk regardless of menopausal status.