Enhancing cohort studies in China and international collaboration

With a population of 1.4 billion-nearly a fifth of the global total-and rapid societal transformations, China is a living laboratory of natural experiments. 2 The country's rising life expectancy, poverty reduction, massive urbanisation, changing social and gender norms, 1 technological advancements, and development trajectory offer unparalleled insights into demography and epidemiology.Large cohort studies in China have exceptional statistical power, and a new BMJ collection (www.bmj.com/collections/cohort-studies-in-china) provides critical reflection and recommendations for the field, including insights on its historical development, 3 international scope, 4 community based cohorts, 5 challenges of balancing scale and quality, 6 and demand for sustainable models, 7 as well as the rise and use of artificial intelligence (AI). 8 The collection calls for enhanced international collaboration, improved data sharing, stronger data governance, long term funding investments, and harmonised study design.The evolution of cohort studies in China from early occupational cohorts (1970-90) to general population studies (1990-2000) to recent explosive growth in large scale initiatives has meant that there were around 350 study cohorts in China in 2024. 3 These cohorts have uncovered wide ranging risk factors for both infectious diseases and non-communicable diseases.China's large population and healthcare system generate vast amounts of clinical data from hospital records. 8 The records produce high granularity data but tend to be focused on patients already seeking care, missing healthier, rural, or access limited groups.Key challenges are data fragmentation, heterogeneity, and lack of standardisation that hinders integration with electronic health records or registries, risking being siloed in hospital information systems. 6 7