New research from the US suggests that smoking soon after waking could increase even a light smoker's risk of lung cancer, because the shorter the time between waking and having a first cigarette, no matter how many you smoke a day, the higher your levels of circulating cotinine, a derivative of nicotine that is made in the body and which has been linked to higher risk of lung cancer. The researchers said that smoking cessation programs should take into account the time smokers waits before they have their first cigarette of the day because it could make a significant difference to their nicotine uptake. The study is the work of Dr Joshua E Muscat, professor of public health sciences at Penn State College of Medicine in Hershey, Pennsylvania, and colleagues, and a paper on it appears in the December issue of Cancer Epidemiology, Biomarkers & Prevention. Muscat told the media that: "Since cotinine levels appear to reflect the risk of lung cancer, our results suggest that smokers who smoke immediately after waking may be especially at risk for lung cancer." "These people may require a more intensive intervention than other smokers to help them quit smoking on a sustained or permanent basis," he added. The blood concentration of the metabolite cotinine is a good indicator of how well our bodies absorb nicotine when we smoke cigarettes. Previous studies have shown there is a wide variation in cotinine levels per cigarette smoked, and the researchers hypothesized that in addition to how often a smoker smokes, there might be other nicotine dependence behaviours that affect cotinine levels, such as time to first cigarette after waking. This in turn could affect a smoker's chances of quitting as well as impacting his or her health. For the study the researchers recruited 252 healthy black and white community-dwelling daily cigarette smokers and examined a number of behaviours that are thought to reflect the urge to smoke. They also measured their plasma and urinary cotinine levels. The results showed that:
- Among one pack per day smokers, there was a 74-fold difference in plasma cotinine levels: from 16 to 1,180 ng/mL.
- Two types of nicotine-dependence was observed in the smokers, "low" and "high".
- The "low" dependents smoked their first cigarette more than 30 minutes after waking, and they nearly all smoked 20 or fewer cigarettes a day.
- Cotinine levels in the low dependent group increased in line with how many cigarettes they smoked per day.
- The "high" dependents smoked their first cigarette of the day within 30 minutes of waking but had a wide range (from 6 to 70) in how many cigarettes they smoked per day.
- The cotinine levels in the high dependent group varied little by cigarette frequency compared with the low dependent group, with a plateau effect appearing for heavy smokers (more than 30 per day).
- After adjusting for cigarette frequency, levels of cotinine went down as time to first cigarette increased, from 437 ng/mL (95 per cent confidence limits [CL] ranging from 380 to 494) for 5 mins or less; 352 ng/mL (95 per cent CL 291-413) for 6 to 30 mins; 229 ng/mL (95 per cent CL 140-317) for 31 to 60 mins; and 215 (95 per cent CL 110-321) for over 60 mins to first cigarette.
- Urinary cotinine varied in a similar fashion.