Association of Greenspace Exposure at Midlife with Cognitive Decline Later in Life in a Study of US Women

Background and aim: Greenspace may slow cognitive decline by increasing opportunities for physical activity and social connection or reducing stress or air pollution. However, studies on the association between greenspace and cognitive decline are sparse. We investigated the prospective association between greenspace at midlife and cognitive decline later in life. Methods: Using data from the US-based Nurses’ Health Study (mean age=61y), we assessed residential greenspace in a 270m buffer as the cumulative average from 1986 to 1994 using Landsat Normalized Difference Vegetation Index data. We examined 16,352 women who were enrolled in a substudy starting in 1995-2001 (74y) through 2008. Participants underwent up to four repeated measures of five cognitive tests. A global composite score was calculated as the average of all z-scores for each task to evaluate overall cognitive functioning. We evaluated the association between greenspace and subsequent cognitive decline using linear mixed models adjusted for age, education, neighborhood socioeconomic status, and depression. Results: In fully adjusted models, those living in the highest quintile of greenspace had an annual slope of decline that was slower by 0.01 units of the global composite score (95%CI 0.00001, 0.012) compared to those in the lowest quintile. To help interpret this estimate, we find that one year of age is related to a -0.01 unit mean annual difference for global cognition; thus, more greenspace appeared equivalent to slowing cognitive aging by one year. We found similar associations for the Telephone Interview for Cognitive Status (TICS); participants living in the highest greenspace quintile had an annual rate of decline that was slower by 0.04 units in the TICS score (95%CI 0.01, 0.07) compared to those in the lowest quintile. Conclusions: Higher greenspace exposure in early adulthood is associated with a slower rate of cognitive decline later in life in this cohort of US women.