Do older children take in more smoke from their cigarettes? Evidence from carbon monoxide levels.

Expired-air carbon monoxide (CO) concentrations were measured in 125 pupils aged 11-17 years attending a girls' comprehensive school in the South of England who had smoked at least one cigarette on the day of testing. Both number of cigarettes smoked on the day of testing and time since the last cigarette were independently related to CO concentrations. Although there was a positive correlation between age and CO, this disappeared when number of cigarettes smoked on the day of testing and time since the last cigarette were taken into account. Previous reports of increasing CO concentrations with age taking account of cigarette consumption may be due to the use of usual daily cigarette consumption rather than number on the day of testing, which is more relevant given the short half-life of CO in the blood. In this sample, no evidence was found for an increase in smoke inhalation with increasing age.