Time to first cigarette after waking and risk of incident chronic respiratory diseases in males: A prospective national cohort study.

INTRODUCTION

While cumulative smoking exposure is a well-established risk factor of chronic respiratory disease (CRD), a behavioral indicator of nicotine dependence, the time to first cigarette after waking (TTFC) may provide additional prognostic information. However, prospective evidence linking TTFC to incident CRD, particularly in Chinese populations, remains limited. This study aims to investigate the association between TTFC and incident CRD risk in middle-aged and older men.

METHODS

This prospective cohort study included 5198 Chinese men aged ≥45 years without baseline CRD who were enrolled in the China Health and Retirement Longitudinal Study (CHARLS). TTFC was categorized as >60, 31-60, 6-30, and <6 minutes after waking, with never smokers as the reference group. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for incident CRD. Laplace regression was applied to evaluate differences in median disease onset time. Joint effects of TTFC and smoking pack-years were also assessed.

RESULTS

During 44105 person-years of follow-up, 856 incident CRD cases occurred (incidence rate: 19.41 per 1000 person-years). Earlier, TTFC was associated with progressively higher CRD risk in a dose-response manner (p for trend=0.025). Compared with never smokers, participants with TTFC <6 minutes had a significantly higher CRD risk (HR=1.31; 95% CI: 1.02-1.66). Laplace regression showed that TTFC <6 minutes was associated with 0.75 years earlier median disease onset (95% CI: -1.45 - -0.06). Joint exposure analysis indicated that participants with both early TTFC and heavy smoking exposure had the highest risk (HR=1.30; 95% CI: 1.10-1.51), with evidence of additive interaction (attributable proportion, AP=0.177; 95% CI: 0.005-0.349).

CONCLUSIONS

Earlier TTFC is independently associated with increased risk and earlier onset of CRD among Chinese middle-aged and older men. TTFC may serve as a simple and potentially informative behavioral marker for identifying smokers with a higher risk of CRD.