Residential Greenness and Breast Cancer Survival after a Breast Cancer Diagnosis

摘要

Background: Natural vegetation, or greenness, has been shown to promote physical activity, social engagement, and cognitive restoration, and reduce ambient pollutants. Greenness was also associated with lower rates of cancer mortality among women. Our objective was to determine if greenness was associated with lower rates of breast cancer mortality. Methods: The Nurses' Health Study II is an ongoing US nationwide prospective cohort study. Participants with Stage l-lll breast cancer diagnosed from 1989-2013 were followed until June 2014 for total and breast cancer specific death. The Normalized Difference Vegetation Index (NDVI) is a satellite-based measure quantifying vegetation density within a 1-km area. NDVI estimates were linked to residential addresses. We calculated time-varying cumulative average greenness from diagnosis until the end of follow-up. We performed multivariate Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (CI) and used restricted cubic splines to explore nonlinear associations. We assessed effect modification by clinical factors, physical activity, population density and region. Results: Among 1,890 breast cancer cases, there were 213 breast cancer deaths and 255 deaths from all causes. Cumulative average greenness was not associated with breast cancer specific mortality (HR for a 0.1-unit increase in NDVI=1.03; 95% CI 0.88,1.21) or all-cause mortality (HR=1.04; 95% CI 0.90,1.19). We observed no modification by clinical factors, population density, and physical activity. While patterns in the Midwest and West suggested benefits for those residing in the highest and lowest levels of green space, results were inconclusive given the small number of events within region. Discussion: The benefits of residential greenness exposure may not extend to breast cancer specific mortality. Regional differences in green space may point to environmental and behavioral differences that should be further explored.