By: Adriana Lein, MSc-GH and Usama Bilal, MD, PhD, MPH
Drexel Urban Health Collaborative and SALURBAL Project  

How are bigger cities different from smaller ones? When cities grow in population do residents become less healthy? Or perhaps healthier? Or maybe there’s no difference? Alternatively, the answer might change depending on the type of illness or other health measure used. Theoretically, and taking into account the enormous diversity of the world’s cities, all of these scenarios are plausible. What is perhaps most useful is understanding the why behind associations between urban population size and growth and human health and how these trends look over time and across different contexts.

Investigating how increasing urbanization levels may impact different areas of health should be a leading question among researchers, public health officials, planners, and policymakers, alike. Urbanization has been one of the most significant global changes over the past fifty years, particularly in the regions of Latin America, Asia and Africa that are urbanizing at much faster rates. These urbanization processes have at times been rapid and unmanaged. As a result, many cities throughout the world are experiencing challenges in areas such as housing quality and informal settlements, transportation planning and sprawl, climate change, and food systems and dietary patterns, all of which have the potential to impact health, health risk factors, and health behaviors.

Urban scaling research examines how these characteristics of city environments- and many others (i.e. socioeconomic indicators, land use, infrastructure) change as a function of city size. Urban scaling is informed by two key ideas. The first is that cities are highly complex systems in which dynamic networks, pathways and feedbacks give rise to patterns in health and other areas (i.e. food consumption, transport, energy use, crime). The second is that cities are greatly varied in size and form and, likewise, their properties are accordingly differentiated. However, current understandings of scaling suggest that if we know a few measurable characteristics of cities- such as population size or wealth estimates- we can accurately predict how some of its characteristics will scale. Some health outcomes- infectious disease, traffic accidents and violence-have received more attention for their scaling patterns. However, the effects of urban scaling and its associated properties (i.e. wealth, productivity, social networks, pollution, housing markets, and others) on a wider range of health outcomes has yet to be explored.

Usama Bilal, MD, MPH, PhD, Assistant Professor at Drexel’s Dornsife School of Public Health is working to change this. Funded by an NIH’s Director’s Early Independence Award, Dr. Bilal is using dating from a sample of around 750 cities in the U.S. and 11 Latin American countries to examine the urban scaling properties of health outcomes and their determinants. These health outcomes will include mortality by causes such as communicable diseases, cardiovascular diseases, traffic injuries, and violence, and prevalence by cardiometabolic risk factors and mental health and substance abuse. His project titled, “The Health Consequences of Urban Scaling” will also give insight into the mechanisms behind any observed relationships. For example, it could be that urban scaling is associated with greater mortality from cancer, but only in cities where scaling lead to increases in air pollution and greater sprawl (which often reduces opportunities for walking/physical activity and leads to greater reliance on automobiles. In other words, does the nature of urban scaling of these health determinants explain the scaling of their associated health outcomes? Perhaps in cities beyond a certain wealth threshold where residents have access to a range of health services, these associations disappear altogether.

Another question that this project will be examining is whether deaths amenable to health care are relatively lower in bigger cities (potentially due to a higher availability of services) but higher in growing cities (if the provision of services has not caught up with population growth). Pricila Mullachery, PhD, MPH, who recently joined the project as Postdoctoral Research Fellow, will be examining these policy-relevant questions.A second component of Dr. Bilal’s research will use systems modeling approaches to study the modified effects of scaling properties on observed health outcomes overtime. These simulation models will illustrate how changes in one scaling property affect others as well as their impacts on outcomes of interest. Such scenario-based modeling is especially relevant to urban policymakers and urban planners as it shows both the proximal and more far-reaching effects of changes to the system (i.e. the influence of a policy or intervention) and has the potential to reveal both expected and unintended results.

Dr. Bilal’s research can help point the way towards the types of policies and interventions likely to be beneficial to health. In many instances, these could come from sources one might not automatically link to health-more efficient transportation systems that lead to cleaner air and support active mobility or upgrades to neighborhood infrastructure to improve safety and encourage physical activity.

The policy implications of this research are many. For example, it can help identifying cities that are outliers and have better (or worse) health outcomes considering their size. Identifying what makes these cities different, in social, built, or policy environments can help provide ideas on how to improve urban health. This research can also help identifying factors that may allow cities to grow (with the added benefits that increased social interactions may have), with a degree of control over the consequences of this growth. More importantly, it can help show that cities do not need to be places of disease, and actually be health-improving environments if the appropriate living conditions are met.

Learn more
The Origins of Scaling in Cities
The New Science of Cities 
Growth, innovating, scaling, and the pace of life in cities 

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