Proximity to freshwater blue space and type 2 diabetes onset: the importance of historical and economic context

Abstract

Background: Living near aquatic areas (blue space) may benefit health by reducing stress and providing physical activity spaces. Salutogenic effects of blue space remain underexplored, particularly in non-coastal and non-urban areas. Methods: We evaluated associations of residential proximity to inland freshwater blue space with new onset type 2 diabetes (T2D) in geographically diverse communities across 37 counties in Pennsylvania, USA, using medical records (2008-2016) to conduct a nested case-control study. T2D cases (n=15,888) were identified from diabetes diagnoses, medication orders, and laboratory test results and frequency-matched on age, sex, and encounter year to diabetes-free controls (n=79,435). Using national hydrography data, we calculated distance (0-0.24, 0.25-0.49, 0.50-0.74, 0.75-1.24, >1.25 miles) from each individual’s residence to the nearest lake, river, tributary, or large stream. Logistic regression models adjusted for community socioeconomic deprivation and other confounding variables. Models were stratified by community type (townships [rural/suburban], boroughs [small towns], city census tracts). Results: Compared with individuals living farthest from blue space, those <0.25 and 0.25-0.49 miles away had higher odds (odds ratio [95% confidence interval]) of T2D in townships (1.13 [1.06, 1.21]; 1.11 [1.03, 1.18]) and boroughs (1.30 [1.17, 1.44]; 1.27 [1.13, 1.41]); in cities, individuals between 0.25-0.74 miles away had higher T2D odds. Residing within the 100-year flood zone and nearest blue space type (river/tributary versus lake) were also associated with higher T2D odds. We observed lower property values for residences nearest the Susquehanna River, the region’s predominant waterbody, but were unable to adjust for property values due to limited data availability. Conclusions: Unmeasured confounding by socioeconomic disadvantage may explain our unexpected findings of higher T2D odds with closer proximity to freshwater blue space. Proximity to blue space may be detrimental to health depending on historic and economic context and interrelated factors such as flood risk, pollution, and lack of waterfront development.