Timing the first cigarette after waking (TTFC), researchers at Kyushu University in Japan found that those who are faster to light up in the morning are more likely to be diagnosed with lung cancer. Nicotine dependence, as indicated by the TTFC, was associated with both adenocarcinoma and squamous/small-cell carcinoma, with the strength of association varying by histologic subtype.

After adjusting for baseline differences, TTFC significantly inversely correlated with lung cancer risk, according to researchers. Using never-smokers as the reference, adjusted odds ratios (ORs) for lung cancer were 1.15, 1.63, 2.42, and 2.76 for TTFC of more than 60 minutes, 31–60 minutes, 6–30 minutes, and 5 minutes or under, respectively, in former smokers and 1.65, 2.67, 4.05, and 6.57, respectively, in current smokers.

The authors also found a significant negative correlation between the number of cigarettes smoked per day and TTFC, suggesting that TTFC is not merely a marker of nicotine dependence but also of tobacco exposure.