Abstract
BACKGROUND: The ratio of the forced expiratory volume in 1 s (FEV(1)) to the forced vital capacity (FVC) is an essential tool for the diagnosis of chronic obstructive pulmonary disease (COPD). However, the relationship between levels of FEV(1)/FVC and mortality in the general population remains unclear, particularly its non-linear relationship. Therefore, we aimed to explore the association between the FEV(1)/FVC and all-cause mortality in the general population. 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(1)/FVC ratio in 0.10 increments. Cox proportional-hazards models were used to estimate the association between the FEV(1)/FVC ratio and all-cause mortality before and after confounder adjustment. Non-linear associations were explored using restricted cubic spline curves. 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(1)/FVC ratio < 0.90 had an increased risk of all-cause mortality compared to those with an FEV(1)/FVC ratio ≥ 0.90. After adjusting for age, sex, body mass index, race, and smoking status, participants in the 0.60 ≤ FEV(1)/FVC < 0.90 group had a lower all-cause mortality risk than those in the FEV(1)/FVC ≥ 0.90 group, while the mortality risk of individuals with an FEV(1)/FVC ratio < 0.50 was higher. Restricted cubic splines revealed a U-shaped association between the FEV(1)/FVC ratio and all-cause mortality. Below and above the inflection point, an inverse trend was observed. CONCLUSION: Our study first revealed a U-shaped association between the level of FEV(1)/FVC and all-cause mortality in general population. CLINICAL TRIAL NUMBER: Not applicable.