The basic characteristics of the study subjects are shown in . Since the current analysis excluded never smokers, there were a larger number of cases than controls (4775 vs. 2835). Lung cancer was more common among men, and about 90% of all subjects were white. Sixty percent of cases and 36% of controls were current smokers. In logistic regression models, the association between the dose of smoking and lung cancer risk showed the expected dose-response pattern. Since the risk is calculated among ever smokers, the ORs are substantially lower than what is typically observed in studies that include never smokers. The OR for current vs. former smoking was 2.32 (95% CI 2.8–2.59). Relative to smoking 1–9 cigarettes per day, the OR was 1.4 (95% CI 1.09–1.8) for 10–19 cigarettes per day, 2.20 (95% CI 1.86–2.59) for 20–29 cigarettes per day, 2.6 (95% CI 2.1–3.2) for 30–39 cigarettes per day, 3.5 (95% CI 2.9–4.3) for 40–49 cigarettes per day and 4.0 (95% CI 1.1–1.5) for 50+ cigarettes per day.
Characteristics of lung cancer cases and controls
Relative to smoking the fist cigarette more than one hour after waking up, the unadjusted odds ratio for lung cancer was 1.78 (95% CI 1.53–2.07 ) for 31–60 minutes and 3.56 (95% CI 3.15–4.03) for 1–30 minutes. There was a significant association between TTFC and sex, age, years of education, smoking status, and pack-years (P<0.01). No significant differences for TTFC by race were found. In multivariate models controlling for sociodemographic characteristics, the pack-year adjusted odds ratios were 1.31 (95% CI: 1.11–1.54) and 1.79 (95% CI: 1.56–2.07) ().
Odds ratios and 95% confidence intervals for lung cancer and time to first cigarette in ever smokers, adjusting for different measures of smoking history.
The results for models using alternative measures of smoking history including total years of smoking, cigarettes per day, smoking status (current vs. former) and years since quitting showed similar results (). The total-smoking years adjusted odds ratio was 1.47 (95% CI: 1.25–1.72) for 31-60 minutes after waking, and 2.34 (95% CI: 2.10–2.68) for within 30 minutes after waking.
The cigarettes per day adjusted odds ratio was 1.58 (95% CI: 1.35–1.84) for 31–60 minutes after waking, and 2.64 (95% CI: 2.31–3.02) for within 30 minutes after waking. The smoking status adjusted odds ratio was 1.68 (95% CI 1.44–1.97) for 31–60 minutes after waking, and 3.0 (95% CI: 2.64–3.42) for within 30 minutes after waking. When smoking was modeled by years since quitting, the risk was 1.66 (95% CI: 1.41–1.94) for 31–60 minutes after waking, and 2.82 (95% CI 2.49–3.42) for within 30 minutes after waking (). In another model that adjusted for total years of smoking and cigarettes per day, the respective odds ratios were 1.40 (95% CI: 1.20–1.66) and 2.12 (95% CI 1.85–2.43).
In whites only, TTFC was statistically significant regardless of the method for smoking adjustment. In blacks, smoking within 30 minutes after waking but not 31–60 minutes after waking was consistently associated with a significant increased risk of lung cancer.
The adjusted ORs associated with each additional year of smoking stratified by the number of cigarettes per day were all statistically significant (P<0.01). The OR was 1.04 for 1–10 cigarettes per day, 1.04 for 11–20 cigarettes per day, 1.06 for 21–30 cigarettes per day, 1.06 for 31–40 cigarettes per day and 1.07 for more than 40 cigarettes per day. The risk of lung cancer associated with TTFC adjusted for the EORs was 1.47 (95% CI: 1.26–1.72) for 31–60 minutes and 2.23 (95% CI: 1.95–2.56). shows the association between the TTFC and lung cancer risk adjusted for the EOR, stratified by seven categories of smoking intensity. The results were consistent with the other models. Compared to a TTFC of 60 or more minutes, the odds ratios were increased for a TTFC of 31–60 minutes and even higher OR were found for a TTFC of 1–30 minutes. The only intensity subcategory where the risk for TTFC was not elevated was for 10–15 cigarettes per day, and 30+ cigarettes per day for just those subjects with a TTFC of 31–60 minutes.
Legend: Time to first cigarette and lung cancer risk in ever smokers adjusting for the excess odds ratio per pack-year, by cigarette intensity (cigarettes per day)
The association between TTFC and lung cancer risk was observed for all major histologic types of cancer (). The odds ratios were slightly higher for the lung histologies that are most strongly related to cigarette smoking including small cell carcinoma and squamous cell carcinoma. Findings for other or mixed histologies are not shown.
Odds ratios and 95% confidence intervals for lung cancer and time to first cigarette in ever smokers by histologic type, adjusting for pack-years of smoking