The associations between blue space exposure and lung function in young adults: a cross-sectional study

The benefits of natural environments for respiratory health are increasingly recognized; however, the effects of blue spaces on young adults’ respiratory health remain understudied. Young adulthood is critical for peak lung function, and exposures during this period may affect later respiratory health. We quantified blue space–lung function associations in Chinese undergraduates. This study aimed to explore the effects of blue space on undergraduates’ lung function using data from the Chinese University Cohort (CUC). A total of 2,422 undergraduates from Binzhou Medical University were included in this study. Blue space exposure from 2016 to 2019 was assessed using a satellite-derived metric indicative of blue space- Modified Normalized Difference Water Index (MNDWI), and lung function was assessed using forced vital capacity (FVC). After adjusting for potential confounders, multiple regression analysis was used to examine the association between blue space exposure and lung function. Compared with the lowest quartile (Q1), the highest quartile (Q4) of current-address residential MNDWI (summer 2019) was significantly associated with higher FVC near home ( β = 118.00 mL; 95% CI: 41.80–195.00) and within 1000‑m ( β = 121.00 mL; 95% CI: 44.90–198.00) and 3000‑m ( β = 83.40 mL; 95% CI: 6.86–160.00) buffers. In the 300‑m buffer, both Q3 and Q4 showed significant increases ( β = 87.20 and 85.90 mL, respectively). For three-year exposure (2016–2019), significant associations were observed in the 300‑m (Q3 and Q4) and 1000‑m (Q4 only) buffers, but not in the 3000‑m buffer. Sex‑stratified analyses revealed significant positive associations in both males and females for certain quartile comparisons, although formal interaction tests did not indicate effect modification by sex. No significant associations were found for school‑address exposures. Supplementary land use/land cover (LULC)‑based analyses detected significant associations only for the 3000‑m residential buffer, with null findings across other scenarios, showing partial discrepancy from MNDWI results. Exposure to environments characterized by higher MNDWI values was associated with better lung function among undergraduates. Our findings support the potential respiratory health benefits of blue space exposure and suggest that integrating blue spaces into environmental planning may promote young adults’ well‑being.