Lung function and mortality in the United States: Data from the First National Health and Nutrition Examination Survey follow up study

Background: A study was undertaken to define the risk of death among a national cohort of US adults both with and without lung disease. Methods: Participants in the first National Health and Nutrition Examination Survey (NHANES I) followed for up to 22 years were studied. Subjects were classified using a modification of the Global Initiative for Chronic Obstructive Lung Disease criteria for chronic obstructive pulmonary disease (COPD) into the following mutually exclusive categories using the forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), FEV₁/FVC ratio, and the presence of respiratory symptoms: severe COPD, moderate COPD, mild COPD, respiratory symptoms only, restrictive lung disease, and no lung disease. Proportional hazard models were developed that controlled for age, race, sex, education, smoking status, pack years of smoking, years since quitting smoking, and body mass index. Results: A total of 1301 deaths occurred in the 5542 adults in the cohort. In the adjusted proportional hazards model the presence of severe or moderate COPD was associated with a higher risk of death (hazard ratios (HR) 2.7 and 1.6, 95% confidence intervals (Cl) 2.1 to 3.5 and 1.4 to 2.0), as was restrictive lung disease (HR 1.7, 95% Cl 1.4 to 2.0). Conclusions: The presence of both obstructive and restrictive lung disease is a significant predictor of earlier death in long term follow up.