Can proximity to blue spaces and cooling centers buffer extreme heat impacts on walking steps?

Abstract Background Extreme heat events can deprive opportunities to go outside, potentially leading to physical inactivity. Multiple adaptation strategies are needed as heat stresses are heterogeneous by socio-demographic groups. This study examined whether proximity to blue spaces (river, sea, or lake) and cooling centers (library, community center, or shopping mall) can buffer the adverse impacts of extreme heat on walking steps. Methods We utilized a nationwide cohort dataset of smartphone application users in Japan, including daily step count records from April 26 to October 25, 2023. We also connected socio-demographic information from survey questionnaires (October or December 2022) and geospatial information such as daily temperature and residential proximity to blue spaces and cooling centers. We categorized the exposure to heat based on a daily maximum of Wet Bulb Globe Temperature: normal days (lower than 28 degrees Celsius), days with heat (28-31), and days with extreme heat (31 or higher). We conducted multilevel mixed-effect linear regression analyses to examine effect modification by proximity to blue spaces and cooling centers (living within 500m or not). We repeated the analyses stratifying by socio-demographic groups (gender, age, and income). Results Among 16,691 participants overall, on days with extreme heat, living close to blue spaces was associated with 30 (95% CI: 6-54) more steps than living far from blue spaces. This pattern was evident in men, young adults, and middle or high-income groups. Proximity to cooling centers did not show effect modification overall. However, it was associated with higher steps for older adults on days with heat and lower steps for women and young adults on days with extreme heat compared to normal days. Conclusions Living close to blue spaces may buffer the adverse impacts of extreme heat on walking steps. Proximity to cooling centers may work similarly for older adults only. Key messages • Living close to blue spaces may buffer reduction in walking steps under extreme heat. • Cooling centers can be shelters against heat for older adults.