Respiratory function in healthy ever-smokers is impaired by smoking habits in a dose-dependent manner.

Background: There is limited information about the respiratory function of ever-smokers without lung disorders. We sought to assess the effects of smoking habits on respiratory function in subjects without lung disorders.

Methods: Subjects were recruited from among patients without any evidence of respiratory disorders who visited rural primary care clinics. Each participant was asked to answer a questionnaire that included questions smoking history. Their forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were measured.

Results: We analyzed 802 subjects (364 men and 438 women). The means of the lambda-mu-sigma method derived z-score of FEV1 (zFEV1) both in current-smokers and ex-smokers were lower than that in never-smokers. The mean zFEV1 in the ever-smokers with more than 30 pack-years of smoking history were lower than that in the ever-smokers with less smoking history. Univariate analysis showed that there were significant negative correlations between pack-years and zFEV1 both in the ex-smokers and current-smokers. There was no significant correlation between the duration of smoking cessation and zFEV1 in the ex-smokers.

Conclusions: Our data suggests that respiratory function in healthy ever-smokers is decreased based on smoking habits in a dose-dependent manner. Even after a long period of smoking cessation, the decreased respiratory function seems to be maintained in ex-smokers.