Abstract
To investigate the association between chronic high temperature exposure and brain structure and how the association influences mental health, we conducted cross-sectional and prospective cohort studies within a sample of 41,552 UK Biobank participants. Chronic temperature exposure was assessed for each participant based on their residential histories and gridded reanalysis temperature data and defined as the percentage of days with a maximum temperature exceeding 27 °C over the last 20 years. Generalized additive models and difference-in-differences approaches were used to estimate the association between chronic high temperature exposure and neuroimaging outcomes obtained via brain MRI. Mediation analysis was performed to assess whether neuroimaging changes mediated the relationship between chronic high temperature exposure and behavioral decline. We observed chronic high temperature exposure was associated with widespread reduced brain volume, including global grey volume (-5859.32 mm³, 95% CI -6631.82 to -5086.83), white matter volume (-5482.47 mm³, 95% CI -6192.92 to -4772.03), regional grey matter volumes (especially in the cerebellum and brainstem), and subcortical structure volumes (especially in the accumbens, hippocampus, and thalamus). Furthermore, the association mediated depression and declined cognition. Chronic high temperature exposure also enhances age-related brain atrophy. Alterations in white matter tracts were also observed. In conclusion, our study provides multimodal MRI evidence of the adverse effects of chronic high temperature exposure on brain structure and mental health.