BACKGROUND: The ratio of the forced expiratory volume in 1 s (FEV METHODS: The data of participants included in the National Health and Nutrition Examination Survey (1988-1994 and 2007-2012 cycles) were analyzed. Participants aged ≥20 years, who were not pregnant, who underwent quality-controlled lung function tests, and with follow-up data on mortality status were enrolled. The study outcome was all-cause mortality. The participants were grouped by FEV RESULTS: Overall, 25,501 participants were included. During the median follow up of 308 months, 6431 (25.2%) deaths were recorded. Among all participants, the mean age is 46.3 years, and 48.7% of which were male. In unadjusted model, individuals with an FEV CONCLUSION: Our study first revealed a U-shaped association between the level of FEV CLINICAL TRIAL NUMBER: Not applicable.