We have characterized that depending on the development and the level of lung function at the age between 20 and 30 years of age, the trajectories of decline in lung function for those with low lung function at early age can lead to COPD at early age. Further, we found that decline in lung function is attenuated in smokers with Hispanic compared to non-Hispanic ethnicity. In Hispanics, this resistance to decline in lung function is directly associated with the percentage of Native American ancestry in Hispanic participants.