Urban heat island and the risk of schizophrenia spectrum disorders in middle-aged and older adults

Abstract

Rapid urbanization and climate crisis amplified the adverse effects of urban heat, while it remained unclear about the long-term impacts of urban heat island (UHI) on mental disorders, especially schizophrenia spectrum disorders (SSD). This study included 393,507 participants from the UK Biobank to examine the impact of long-term exposure to UHI on the incidence risk of SSD and changes of brain structures. UHI exposure were quantified as surface UHI intensity and normalized land surface temperature from satellite data. Cox proportional hazard models and multiple linear regression models were used to examine associations of UHI effects with SSD and changes of brain structures. During a median follow-up of 13.8 years, there were 1112 (0.3 %) participants diagnosed with SSD and 367 (0.1 %) with schizophrenia. Every standard deviation increased surface UHI intensity was associated with a 17 % (HR, 1.17; [95 % CI, 1.07–1.28]) excess risk of SSD and a 26 % excess risk of schizophrenia (HR, 1.26; [95 % CI, 1.08–1.46]). These effects were more pronounced in individuals with a high genetic risk of schizophrenia and those aged <60 years. UHI exposure was also associated with brain macrostructure and microstructure, particularly in the frontal and temporal lobes, as well as white matter tracts. In this cohort study of middle-aged and older adults, UHI exposure was identified as a risk factor for the onset of SSD and schizophrenia. These findings highlight the need for implementing initiatives of UHI mitigation and heat resilience to improve mental health and sustainable development in urban communities worldwide.