The impact of urban green and grey spaces on mental health: insights from the inhabitants of Rome

This study, conducted within the framework of the Rome Longitudinal Study, explores the intricate relationship between urban greenness and mental health, offering groundbreaking insights into how different environmental elements influence mental health-related outcomes. The study distinguishes itself by employing both 2D and 3D indicators to evaluate the impact of green and grey spaces on the mental health of a substantial population-based cohort. The data set encompasses 593,894 Italian adults aged 30 years and above. The mental health outcomes were meticulously defined using two primary sources: prescription records (encompassing a range of psychiatric medications such as antidepressants, antipsychotics, mood stabilisers including lithium, and anxiolytics, hypnotics, and sedatives) and hospitalization records (specifically focusing on conditions like schizophrenia spectrum disorder, depression, anxiety, stress-related and somatoform disorders, and substance use disorders). The study's innovative approach involved the use of varied indicators of environmental exposure, including the 2D indicators (e.g. Normalized Difference Vegetation Index, NDVI) and 3D indicators derived from LiDAR data (green and grey volume, tree count, and the Normalized Difference Green-Grey Volume Index), all measured in the vicinities of the participants’ residences. The conclusions drawn from this study underscore the significant impact of urban green spaces in mitigating the use of drugs for psychiatric conditions. Conversely, greater exposure to urban grey spaces is linked to an increased usage of such medications. These findings highlight the critical need for accurate characterisation and understanding of green and grey spaces within urban environments, using novel and comprehensive exposure indicators.