Both air pollution and residential greenness have been shown to affect health, whereas more prospective cohort studies are warranted for causal pathways. Furthermore, how environmental factors and lifestyle behaviours interact to cause or modulate dementia and mental disorder remains unclear. Due to environmental exposure and lifestyle vary by contexts of geography and cultures, this geography-culture-related heterogeneity should be considered in studies of the relationship between environmental exposure and lifestyle with mental health and dementia. Although few comparative studies have been conducted among multicultural populations, the conclusions are mixed and with no inclusion of Asian countries. In recent years, more and more data on lifestyle, environmental exposure, mental health, and dementia outcomes is available in the UK biobank providing an effective way for us to conduct a multinational comparative analysis. In this study, we aim to assess the correlation between environmental exposures (air pollution and residential greenness) and lifestyle (physical activity, dietary pattern, nutritional supplementation, sleep pattern, smoking, and alcohol use) with the health outcomes of dementia and mental disorder using Cox proportional hazards models, adjusted for a range of covariances. We aim to clarify the following questions: what are the different characteristics in the development of depressive disorder and dementia between Asian and European populations; which environmental and lifestyle factors contribute to the differences in the development of depressive disorder and dementia; how environmental factors and lifestyle behaviors interact with each other and whether the potential patterns of synergistic effects between air pollution, greenness, and lifestyle are different in different ethnic populations. The project will be divided into several sub-projects and is expected to last approximately 3 years. To our knowledge, our study is the first multinational comparative study including European and Asian populations to examine the association between environmental exposure and lifestyle with the occurrence of dementia and mental disorder, which will provide a template for future international comparative studies. We hope our multinational study would help provide new directions for green space planning, air pollution control, and better mental disorder and dementia prevention.
