Background: Chronic obstructive pulmonary disease (COPD) is characterized by chronic airflow limitation. The prevalence of airflow limitation in Japan is 10.9% (16.4% of males and 5.0% of females). Cigarette smoking is well known as a major cause of COPD. However, few epidemiological studies have evaluated the effects of cigarette smoking on pulmonary function in healthy subjects.
Methods: Subjects aged 40 years or older (n=2,917), who had participated in a community-based annual health check in Takahata, Japan, from 2004 through 2005, were enrolled in the study. The smoking histories of these subjects were investigated using a self-reported questionnaire. Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV(1)), and forced expiratory flow at 25-75% of FVC (FEF(25-75)) were measured by standard procedures using spirometric machines.
Results: There were 554 current smokers (18.6%) and 403 former smokers (13.8%). The prevalence of airflow limitation defined by FEV(1)/FVC <0.7 in this population was 10.6%, and prevalence of airflow limitation defined by 5th percentile lower limit of normal was 6.4%. In smokers, percent predicted values of measured spirometric parameters (%FVC, %FEV(1) and %FEF(25-75)) decreased significantly with age, except for male %FVC. Also, percent predicted values of measured spirometric parameters decreased significantly with increasing pack-years, except for female %FEF(25-75).
Conclusion: Cigarette smoking increased the prevalence and severity of airflow limitation. It is concluded that cigarette smoking increases the risk of airflow limitation in a healthy Japanese population.