Summer temperatures, depressive symptoms, and health-related quality of life: a study of residents in 263 Chinese cities.

Against the backdrop of global climate warming, the impact of summer heat on urban residents' health has become increasingly prominent. Given that existing studies, while confirming the adverse health effects of high temperatures, have failed to elucidate the specific mechanisms, resulting in policy interventions that remain largely confined to macro-level warnings without precise pathways, conducting mediation research is crucial for exploring potential explanatory pathways and informing public health strategies. Based on data from 106,949 residents across 263 Chinese cities, this study investigates the associations of summer temperature fluctuation in urban areas on health-related quality of life (HRQoL) and its potential explanatory pathways. The findings reveal that monthly fluctuations in summer urban temperatures exhibit a significant negative correlation with residents' HRQoL, with temperatures above the seasonal average leading to a marked decline in HRQoL (β = -0.169, p = 0.006). Additionally, high temperatures are significantly associated with increased depressive tendencies among residents (β = 0.709, p = 0.003). More importantly, our analysis showed a statistical mediation pattern, with depressive symptoms mediating the relationship between temperature and HRQoL(indirect effect = -0.066, 95% CI [-0.025, -0.112]). The study further confirms that the impact of summer temperature on HRQoL follows a linear rather than U-shaped pattern, underscoring the importance of seasonal analysis. These findings provide empirical evidence relevant to climate-adaptive public health policies, implying that mental health interventions, particularly for depression-prone populations, could be considered for inclusion in high-temperature risk management. Through a multi-city, large-sample design, this study offers new insights into the complex relationship between climate change and urban residents' health.