Urban metabolic health vulnerability: how cities transmit global shocks into population health

Cities are not only exposed to the health consequences of climate change and geopolitical disruption. They also shape, amplify, and redistribute those consequences through the metabolic flows that sustain urban life: food, water, energy, and pharmaceuticals. This paper argues that urban metabolism remains an undertheorised mediating layer in planetary health scholarship. Using the ongoing Strait of Hormuz closure as an illustrative case, it shows how geopolitical shocks can move through urban supply chains and translate into population-level health risks. The current separation between urban systems research, supply chain vulnerability, and planetary health creates important governance blind spots. Many cities import most of their food, while also depending heavily on external pharmaceutical and energy supplies. These dependencies are especially acute in Small Island Developing States, where exposure to disruption is structurally high. The paper proposes Urban Metabolic Health Vulnerability as a framework linking geopolitical risk assessment with municipal health protection. It is organised around three dimensions: metabolic dependency, buffer capacity, and health transmission sensitivity, and is presented as a conceptual scaffold for further empirical validation and expert co-design.