What health are we talking about? Biodiversity as the missing link between One Health and Planetary Health.

Health has become a central term in global sustainability policy, yet it is often used without sufficient conceptual precision. Public health, global health, One Health, EcoHealth, GeoHealth, and Planetary Health each emphasize different dimensions of the relationship between humans, animals, and the environment. In policy contexts, however, these distinctions are frequently blurred. We argue that biodiversity is often treated as an environmental co-benefit rather than as a foundational determinant of health. This weakens the implementation of One Health approaches because biodiversity underpins disease regulation, immune system development, food and water security, ecosystem functioning, resilience, and climate adaptation. At the same time, biodiversity provides a critical link between One Health and broader Planetary Health challenges, including global environmental change and the transgression of planetary boundaries. Future health and sustainability policies should move beyond generic references to health and explicitly recognize biodiversity as part of preventive health systems.