Urban Scaling of Health Outcomes: a Scoping Review

Abstract

Urban scaling is a framework that describes how city-level characteristics scale with variations in city size. This scoping review mapped the existing evidence on the urban scaling of health outcomes to identify gaps and inform future research. Using a structured search strategy, we identified and reviewed a total of 102 studies, a majority set in high-income countries using diverse city definitions. We found several historical studies that examined the dynamic relationships between city size and mortality occurring during the nineteenth and early twentieth centuries. In more recent years, we documented heterogeneity in the relation between city size and health. Measles and influenza are influenced by city size in conjunction with other factors like geographic proximity, while STIs, HIV, and dengue tend to occur more frequently in larger cities. NCDs showed a heterogeneous pattern that depends on the specific outcome and context. Homicides and other crimes are more common in larger cities, suicides are more common in smaller cities, and traffic-related injuries show a less clear pattern that differs by context and type of injury. Future research should aim to understand the consequences of urban growth on health outcomes in low- and middle-income countries, capitalize on longitudinal designs, systematically adjust for covariates, and examine the implications of using different city definitions.

Keywords: City growth; City size; Complex systems; Urban health; Urban scaling; Urbanization.

Fig. 1

Example of three urban scaling relationships (superlinear for homicides, linear for traffic deaths, and sublinear for suicides). Footnote: Data simulated using scaling coefficients from Melo et al. [89] for Brazilian cities

Fig. 2

PRISMA flowchart. Footnote: Wrong exposure refers to studies that do not have a city size or growth exposure. Wrong outcome refers to studies not using a health outcome. Wrong type of paper refers to editorials or opinion pieces. Purely rural comparison refers to studies that do not compare cities, but only urban and rural areas. Wrong setting refers to studies that were not set in cities