The associations of healthy lifestyle index with breast cancer incidence and mortality in a population-based study

Purpose: To investigate how a healthy lifestyle index (HLI) is associated with breast cancer risk and survival in a population-based breast cancer study. Methods: The study included 1319 breast cancer cases and 1310 controls from the population-based Long Island Breast Cancer Study Project and its follow-up study where vital status was ascertained using the National Death Index (521 deaths, 210 from breast cancer; median follow-up 214.5 months). HLI scores were generated from body mass index, physical activity, intake of plant and animal foods, alcohol consumption, breastfeeding, and smoking, with higher values corresponding to healthier behaviors obtained from baseline questionnaire. Multivariable logistic and Cox regression models were used to estimate breast cancer odds ratios (ORs) and mortality hazards ratios (HRs), respectively. Results: Compared to women in the low HLI tertile, a significant reduction in risk of breast cancer was observed for women in the intermediate (OR = 0.78, 95% CI 0.64–0.93) and high (OR = 0.73, 95% CI 0.60–0.88) tertiles; a one-point increase in HLI score was associated with a 14% reduction in breast cancer risk (OR = 0.86, 95% CI 0.80–0.93). For survival, a significant reduction in all-cause mortality was also observed in women in the intermediate (HR = 0.68, 95% CI 0.56–0.84) and high (HR = 0.72, 95% CI 0.58–0.88) HLI tertiles with a 17% reduction in all-cause mortality (HR = 0.83, 95% CI 0.76–0.91) for one-point increase in HLI score. These inverse associations were more prominent among postmenopausal women. Conclusion: A healthy lifestyle is beneficial not only in reducing breast cancer risk but also in improving overall survival after breast cancer diagnosis, especially among postmenopausal women.