Bao Li Gu 2025

“The current study used data from the UK Biobank, a large population-based research resource focused on health-related outcomes in the period of middle age and later life. More than nine million eligible individuals who have registered in the UK National Health Service across England, Scotland, or Wales were invited to participate, and about half a million individuals aged 39–73 enrolled in baseline assessment during 2006–2010.”

Translation

The researchers used health information from the UK Biobank, which is a very large health database in the UK. They studied about half a million adults between ages 39 and 73. They used this information to examine whether living in hotter city areas was connected to mental health problems.

“The urban heat island (UHI) effect, characterized by elevated temperatures in urban centers that radiate outward to surrounding areas, is a focal issue in densely populated cities (Tuholske et al. 2021). This phenomenon is predominantly attributed to the built environment (e.g., extensive impermeable surfaces, high concentration of concrete structures, three-dimensional urban structures, limited green and blue spaces) and human-induced heat emissions (e.g., from vehicles, industries, and air conditioning systems) (Iungman et al. 2024; Oke et al. 2017). Against the backdrop of intensified extreme heat, the UHI effect poses threats to various aspects of urban life, including energy consumption, ecosystems, and human well-being, ultimately affecting urban sustainability (Haddad et al. 2024).”

Translation

Urban heat island means cities become hotter than nearby surrounding areas. This happens because of buildings, roads, concrete, cars, industries, and air conditioners producing heat. This extra heat can affect people’s health, the environment, and overall well-being, including mental health.

“Specifically, every SD increase in summer UHII heightened 4% (95% CI, 3–5%) higher incidence rates of mental disorders, 12% (95% CI, 11–14%) higher rates of substance use disorder, 8% (95% CI, 6–10%) higher rates of depressive disorder, and 6% (95% CI, 4–8%) higher rates of anxiety disorder.”

Translation

The results showed that when city heat increased, mental health problems also increased. Hotter urban areas were linked to more cases of depression, anxiety, substance use problems, and other mental disorders. This means higher city heat can make mental health worse.

“UHI represents a prolonged form of long-term heat effect, driven by urbanization, and potentially provides a more consistent and negative impact on mental health (Mirzaei et al. 2020; Wong et al. 2017; Wong et al. 2018).”

Translation

UHI represents a prolonged form of long-term heat effect, driven by urbanization, and potentially provides a more consistent and negative impact on mental health (Mirzaei et al. 2020; Wong et al. 2017; Wong et al. 2018).

Future research should study people from different countries and climates to see if urban heat affects mental health the same way everywhere. Researchers should also include other environmental factors like humidity, dry heat, and time spent outdoors to better understand how heat exposure affects mental health. More studies should also test which city planning solutions, like more trees and green spaces, work best to reduce these mental health risks.

The most difficult part to understand was the statistical analysis, especially the time-dependent Cox regression models and the structural equation model (SEM). It was challenging to understand how these models were used to measure the relationship between urban heat exposure and mental disorders, and how psychiatric symptoms were tested as early indicators between heat exposure and mental illness.