Lung function and symptoms of cigarette smokers related to tar yield and number of cigarettes smoked.

In a survey of over 18 000 male civil-servants, tar yield and number of cigarettes smoked daily were related to lung function and respiratory symptoms. Both phlegm production and airflow obstruction among smokers increased with daily cigarette consumption. Tar yield influenced phlegm production but not the degree of airflow obstruction. However, those smoking more than twenty cigarettes per day lost most of the advantage of smoking low-tar cigarettes since their phlegm production was the same as that of high-tar cigarette smokers. Ex-smokers had better lung function than current smokers with comparable total cigarette consumption; the difference between ex-smokers and current smokers was not related to the length of time that ex-smokers had abstained from smoking. Despite a reduction in phlegm production a change to low-tar cigarettes, may only be associated with an improvement in lung function if dialy cigarette consumption is also reduced. After stopping smoking there may be an initial improvement in lung function but ex-smokers never fully restore their lung function, no matter how long they have abstained from smoking. Although lower tar yield may reduce phlegm production and the risk of cancer, the development of airways obstruction may not be related to the tar content of cigarettes. Rather, the gaseous phase of tobacco smoke may contain the irritant agents leading to airways obstruction.