TTFC is a measure of nicotine addiction, but it has been largely absent from epidemiologic investigations of lung disease, including a systematic review of smoking and COPD [23]. To our knowledge, ours is the first to investigate the association between TTFC and COPD in a substantial sample from a large representative cohort. Consistent with our findings are reports that shorter TTFC is associated with family history of COPD [24] and increased risk of lung [9, 10, 25, 26] and supraglottic cancers [27].
