This study investigates the lung-function trajectories leading to chronic obstructive pulmonary disease (COPD) in three independent cohorts: the Framingham Offspring Cohort, the Copenhagen City Heart Study, and the Lovelace Smokers Cohort. The researchers stratified participants based on their forced expiratory volume in 1 second (FEV1) at cohort inception (mean age 40 years) and the presence or absence of COPD at the last study visit. They found that among those with an FEV1 of less than 80% of the predicted value before 40 years of age, 26% developed COPD after 22 years of observation, compared to 7% among those with an FEV1 of at least 80% of the predicted value. Approximately half of the participants with COPD had a normal FEV1 before 40 years of age and a rapid decline in FEV1 thereafter, while the other half had a low FEV1 in early adulthood and a subsequent slower decline. The study suggests that low FEV1 in early adulthood is important in the development of COPD, and that accelerated decline in FEV1 is not a necessary condition for COPD.This study investigates the lung-function trajectories leading to chronic obstructive pulmonary disease (COPD) in three independent cohorts: the Framingham Offspring Cohort, the Copenhagen City Heart Study, and the Lovelace Smokers Cohort. The researchers stratified participants based on their forced expiratory volume in 1 second (FEV1) at cohort inception (mean age 40 years) and the presence or absence of COPD at the last study visit. They found that among those with an FEV1 of less than 80% of the predicted value before 40 years of age, 26% developed COPD after 22 years of observation, compared to 7% among those with an FEV1 of at least 80% of the predicted value. Approximately half of the participants with COPD had a normal FEV1 before 40 years of age and a rapid decline in FEV1 thereafter, while the other half had a low FEV1 in early adulthood and a subsequent slower decline. The study suggests that low FEV1 in early adulthood is important in the development of COPD, and that accelerated decline in FEV1 is not a necessary condition for COPD.