In summary, TTFC was significantly associated with COPD after simultaneous adjustment for established smoking factors and COPD risk factors; current smokers with shorter TTFC had greater risk of COPD compared to those with longer TTFC (>60 minutes). Although current smokers are at high risk for developing COPD, not all smokers develop COPD [8]. Identification of subgroups of smokers at greatest risk of COPD may help to target clinical screening for this disease, to reduce the number of undiagnosed cases, and thus allow for targeted interventions which may slow the disease progression. Our data suggest that TTFC may provide additional useful information about COPD risk. However, additional studies set in other populations, including former smokers, are needed to confirm our findings. Large prospective studies that define COPD using spirometry are particularly needed.
