Late Breaking Abstract - Associations of residential green space with incident asthma and the role of air pollution: Evidence from UK Biobank and Chinese C-BIOPRED study

<bold>Background:</bold> Green spaces represent a recently modifiable environmental factor. There is limited evidence regarding the relationship between it and the risk of asthma. <bold>Objectives:</bold> To assess the long-term association between residential greenness and incident asthma. <bold>Methods:</bold> Residential green space was indicated by the percentage of green space at a 300 m buffer. Casual mediation analysis was used to quantify the indirect effect of air pollution. The interactive effects between the genetic risk of asthma and residential greenness were investigated. In Chinese C-BIOPRED, the normalized vegetation index (NDVI) was used to quantify the residential greenness and we explored the association between NDVI and severe asthma. <bold>Results:</bold> Of 363,730 participants, 10,592 incident asthma cases were identified with 12.4 years of follow-up. Individuals who were exposed to residential green space in the highest level had a 13.0% lower risk of incident asthma. This association was modified by NO₂, with green space indicating a protective effect in lower NO₂ levels. PM_2.5 had a mediation effect of 31.5%. We did not identify any interactive effects between genetic risk and residential greenness on incident asthma. No significant association was found between NDVI and severe asthma in the overall C-BIOPRED population; however, after including non-smokers only, NDVI was significantly associated with a reduced risk of severe asthma. <bold>Conclusion:</bold> Elevated residential greenness was associated with a lower risk of asthma, and air pollution played an important role in it. Developing sustainable natural environments might benefit populations’ respiratory health.