A new study says that smokers who light up immediately after waking up may be at higher risk of lung cancer than those who wait, regardless of the number of cigarettes smoked.
To reach the conclusion, scientists measured smokers' levels of cotinine, a by-product of nicotine, which has been shown to reflect the risk of developing lung cancer.
"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," said researcher Joshua E. Muscat, Ph.D., M.P.H., professor of public health sciences at Penn State College of Medicine.
Nicotine levels in the blood can be measured biochemically by the concentration of the metabolite cotinine.
Muscat and colleagues conducted a community-based study in Westchester County, N.Y., to examine whether a behavioural aspect of nicotine dependence (the amount of time to the first cigarette after waking up) affects the physiological uptake of nicotine.
This in turn may affect one's success in quitting smoking and have multiple health effects, such as lung cancer.
The study included 252 healthy black and white people who were daily cigarette smokers. Researchers examined a number of behavioural factors that are thought to measure the urge to smoke, and results showed a clear trend between lighting-up earlier and higher cotinine levels.
Cotinine levels varied from 16 ng/mL to 1180 ng/mL - a 74-fold difference, according to the study. Participants who waited 30 minutes or more were categorized into the "low" dependant phenotype; those who smoked within the first 30 minutes of waking were considered "high." Number of cigarettes smoked per day and its association with cotinine levels varied as well.
"Not all smokers are the same and approaches to smoking reduction may need to account for individual smoking behaviours such as the intensity and frequency of puffing, cravings and physiological symptoms," said Muscat.
"It is unclear why smokers who take their first puff immediately after waking have higher cotinine levels, but this may reflect a more intense pattern of smoking. We need to find out why this is," Muscat added.
The study has been published in Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research, as part of a special tobacco focus in the December issue.