The Effect of Nighttime Heatwave on Poststroke Disability in Subtropical Cities of China

Although short-term exposure to heatwaves has been linked to an elevated risk of stroke onset, evidence regarding the long-term impact of heatwave exposure on poststroke disability remains limited, particularly for nighttime heatwaves. We conducted a cross-sectional study that included 29,447 participants from the Guangdong Province High-Risk Population Screening and Intervention Project for Stroke (2016-2021). Using a generalized additive model, we compared the effects of long-term exposure to heatwaves between daytime and nighttime on poststroke disability, as measured by modified Rankin Scale (mRS) scores. Furthermore, we projected the future burden of poststroke disability attributable to heatwave changes under different climate change scenarios. Both long-term exposure to daytime and nighttime heatwaves increased poststroke disability risk. Specifically, each additional day of nighttime heatwave was associated with an excess risk (ER) of 4.62% (95% CI: 4.36%-4.89%) in poststroke disability, which is higher than daytime heatwave (ER = 3.71%, 95% CI: 3.46%-3.97%). Similarly, for each 1 °C increase in heatwave intensity, the risk was also greater for nighttime heatwaves (ER = 4.36%, 95% CI: 4.01%-4.72%) than for daytime events (ER = 1.60%, 95% CI: 1.45%-1.76%). Subgroup analyses revealed similar patterns. Projections indicate that global warming will escalate heatwave-related poststroke disability burden, with greater burden for nighttime heatwaves than daytime events. For instance, under the SSP5-8.5 scenario by the 2080s, the projected increases in the attributable fraction (AF) for both nighttime heatwave duration (15.63%, 95% eCI: 13.39%-17.99%) and intensity (14.86%, 95% eCI: 12.73%-17.11%) were higher than those for daytime heatwaves (5.22%, 95% eCI: 4.47%-6.01% for heatwave duration; 12.68%, 95% eCI: 10.86%-14.60% for heatwave intensity). These findings highlight nighttime heatwave as a critical and underaddressed risk factor for poststroke outcomes in the context of climate change.