Time of 1st cigarette points to cancer risk
Smokers who reach for their first cigarette within 30 minutes of waking up have a much greater risk of developing head, neck, and lung cancer, say U.S. scientists.
The research, led by Joshua Muscat of Penn State College of Medicine in Hershey, Pa. is described in two papers published online today in the journal Cancer.
Muscat says data for the two studies, which included more than 9,400 individuals, were collected from medical centres in New York City between 1977 and 1999. A questionnaire was also used to assess smoking habits.
Patients newly-diagnosed with cancer were recruited to the studies and then matched with control subjects who were being treated at the hospitals for a wide range of conditions unrelated to tobacco smoke.
All study participants were either current or former smokers.
Early morning smokers
Their first analysis of patients diagnosed with lung cancer revealed those who smoked their first cigarette within 30 minutes after waking were 1.79 times as likely to develop lung cancer than those who had held off smoking for an hour or more.
Smokers who lit up between 31 and 60 minutes after waking had a 1.31 times increased relative risk of developing lung cancer.
Their second analysis of head and neck cancer study data yielded similar findings.
Individuals who smoked within 30 minutes of waking and those who smoked between 30 and 60 minutes after waking were 1.59 and 1.42 fold more likely to develop cancer respectively when compared with those who waited an hour or more.
Muscat says the issue is not so much the frequency of smoking, rather it's the way cigarettes are smoked.
He adds the studies' results do not suggest that by delaying the time to first cigarette (TTFC) a smoker can delay their cancer risk.
"It's not a voluntary thing. People smoke because they are highly dependent," Muscat tells the Australian Broadcasting Corporation.
"They really don't have the option of waiting, they wake up and crave cigarettes and they smoke, it's not a behaviour that is modifiable."
"We think the early morning smokers are more nicotine dependent and unlikely to change their smoking habits."
The papers' authors suggest that this high risk group of individuals would benefit from targeted smoking interventions.
Muscat says the reason why the early morning smokers have a greater risk of developing cancer is: "not because they are smoking more frequently or for a greater number of years, but rather it represents a smoking behaviour that seems to reflect the intensity of smoking." This leads to increased carcinogen exposure.
Previous studies have shown highly nicotine-dependent individuals have significantly more cotinine, the major breakdown product of nicotine, in their blood.
The researchers say the TTFC can be used as a proxy measure for this dependence because it is associated with the uptake of nicotine and tobacco smoke.
Muscat now plans to measure smoking intensity through the use of machines that record the frequency of puffing and how deeply the smoke is inhaled.
Professor Lin Fritschi, an epidemiologist at the Western Australian Institute for Medical Research, says that it appears the TTFC is a reasonable marker for lung cancer, but it is not a particularly good measure for head and neck cancers.
"There's not such a strong statistical significance for this finding," she says.
Fritschi says the data appears to show that the relative risk of developing cancer is approximately the same regardless of whether the subjects are current or former smokers.
"The TTFC data that is adjusted for smoking status [current versus former] is combined, but if you keep smoking the risk of cancer will keep going up; whereas for former smokers the risk of cancer will be declining with time," explains Fritschi.
"It would have been interesting and useful to have had the unadjusted information."