A collaborative research team led by the School of Public Health of Shanghai Jiao Tong University, with Capital Medical University and Imperial College London, recently conducted an epidemiological assessment of the association between long-term urban heat island (UHI) exposure and the risk of mental disorders among middle-aged and elderly adults. The findings, published in two peer-reviewed journals, Environment International and Urban Climate, provide novel epidemiological evidence on the potential link between urban microclimates and mental health. The studies highlight the urgent need to incorporate UHI mitigation strategies, such as expanding green spaces and optimizing urban spatial configurations, into urban planning and development to enhance public mental health and promote sustainable urban growth.
With rapid urbanization reshaping the earth’s surface and altering local climate systems, more than half of the global population now resides in urban areas. High building density, heavy traffic, and emissions from industrial and residential sources disrupt the surface energy balance and alter heat flux dynamics. These changes, compounded by reduced vegetation cover and increased impervious surfaces, drive the UHI, a phenomenon characterized by systematically higher temperatures in urban cores compared to surrounding rural areas, presenting a significant spatial temperature gradient. As one of the most persistent and pronounced manifestations of urban microclimate change, UHI not only destabilizes local climate systems but also poses various environmental and public health threats, including increased energy consumption, exacerbated air pollution, accelerated ecological degradation, disrupted circadian rhythms, and heightened chronic disease risks. With the global burden of mental illness steadily rising, increasing attention is being paid to the deeper psychological and social impacts of urban microclimate changes. “Eco-anxiety”, an emerging psychosocial response to the climate crisis, reflects urban residents’ growing concern over reduced quality of life, psychological stress, and uncertainty brought on by environmental imbalances. While prior studies have linked UHI to mortality and cardiovascular outcomes, systematic investigations into the mental health impacts of long-term UHI exposure remain limited.
The studies employed the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-derived land surface temperature (LST) and land cover data to estimate participants’ individual UHI exposure through indicators such as UHI Intensity and standardized LST (LSTnorm) during summer daytime. Statistical analyses were conducted using Cox proportional hazards models, multiple linear regression models, and logistic regression models to examine the associations of UHI exposure with incidence risks of mental disorders, brain phenotypes involving brain macrostructure (cortical and subcortical cortexes) and microstructure (white matter tracts), as well as changes in psychiatric symptoms. Moreover, the study introduced polygenic risk scores to quantify individual genetic susceptibility and further investigated the interaction effects between genetics and UHI exposure on mental health. Structural equation modeling (SEM) was also utilized to explore the pathways through which UHI-related psychiatric symptoms may mediate the risk of mental illness.
Results in the analyses demonstrated that each standard deviation (SD) increase in UHI intensity elevated the incidence risks of mental disorders, including substance use disorder (12%), depressive disorder (8%), anxiety disorder (6%), and schizophrenia spectrum disorders (17%). Of note, exposed to long-term UHI, individuals with high genetic risk for schizophrenia spectrum disorders exhibited even higher incidence risk, suggesting a potential interaction effect between heat exposure and genetic susceptibility in the onset of psychiatric disorders. These findings offer crucial insights for urban health risk management, highlighting the need to incorporate the identification of vulnerable populations and the implementation of precision prevention strategies into urban climate adaptation policies and microenvironmental intervention strategies. This approach would more effectively mitigate UHI-related health inequalities and enhance the health resilience of sustainable urban development.
Regarding brain imaging phenotypes, the increase in UHI intensity was significantly related to the changes in white matter tracts, particularly white matter tract integrity impairment or structural alterations in critical neural pathways such as the inferior longitudinal fasciculus. It was suspected that prolonged heat exposure might induce chronic heat stress responses in the body, leading to vascular endothelial dysfunction, oxidative stress, and the activation of neuroinflammatory responses, ultimately resulting in increased blood-brain barrier permeability. This process might facilitate the abnormal entry of inflammatory factors and plasma proteins into the central nervous system, causing serum protein leakage, brain edema, and focal demyelination, thereby adversely impacting the white matter microstructure. Moreover, the studies suggest that the impact of UHI on white matter tracts might be partially attributed to substance abuse behaviors, particularly opioid use, which has been shown to exacerbate white matter damage and neuroaxonal degeneration by inducing hypoxic conditions, vascular inflammation, and neurotoxic reactions. The above findings provide new ideas for exploring the potential mechanisms through which UHI might impact brain structure and increase the risk of psychiatric disorders, laying a theoretical foundation and direction for further mechanistic studies. In addition, the results of SEM revealed that UHI exposure might increase the risk of psychiatric disorders by exacerbating symptoms of depression and anxiety or diminishing individuals’ subjective well-being, emphasizing the necessity of early symptom intervention for mental health protection.
These findings provide critical insights into the relationship between urban microclimates and mental health, identifying UHI as a key environmental stressor contributing to psychiatric morbidity. The findings call for forward-looking, climate-resilient urban planning strategies to mitigate the psychological burden of UHI. Such strategies should extend beyond mere infrastructure optimization, encompassing the construction of robust public mental health systems. The team advocates for the integration of climate-resilience principles into urban design, prioritizing green and blue infrastructure, spatial optimization, and novel heat-mitigating materials to reduce thermal stress. Comprehensive, equity-focused public health policies are essential to ensure adequate support for vulnerable populations. These interventions are expected to improve urban thermal comfort, strengthen population-level psychological resilience, and support the development of a “brain-healthy city” where health and inclusiveness can thrive under sustainable environmental conditions.
The corresponding author for both publications is Dr. Jinjun Ran from the Shanghai Jiao Tong University’s School of Public Health. Other corresponding authors include Prof. Shengzhi Sun from the Capital Medical University’s School of Public Health and Dr. Lefei Han from the Shanghai Jiao Tong University’s School of Global Health. The co-first authors are graduate students, Yujia Bao and Yongxuan Li, from the Shanghai Jiao Tong University School of Public Health. Additional co-authors include Prof. Chen Shen from Imperial College London, Prof. Xiaobei Deng from the Shanghai Jiao Tong University School of Public Health, and Jiawei Gu from the Shanghai Jiao Tong University School of Public Health. This work was supported by the National Natural Science Foundation of China, grant number 82304102; Natural Science Foundation of Shanghai, grant number 23ZR1436200; and Shanghai Science and Technology Development Fund, grant number 22YF1421100.