Background and Objective Chronic obstructive pulmonary disease has been increasing throughout the world. Many studies show that smoking accelerate decline in pulmonary function and smoking cessation can improve it, but there are very few studies focusing effect of smoking cessation in Japanese people. Therefore we investigated influence of smoking/smoking cessation on pulmonary function.

Subjects and Method Subjects were 3913 (55.7±10.5 years old) male who underwent medical check-up in a hospital during 2004. We compared pulmonary functions with stratified analysis among 1096 current smokers (CS), 1706 ex-smokers (ES) and 1111 never smokers (NS) using ANOVA.

Result There were significant differences respectively among the three groups, in the following order of NS, ES, CS: FEV_1.0 (Forced Expiratory Volume in 1 second) %: 82.8±5.9, 80.5±6.8, 79.8±7.2, %FEV_1.0, Peak Flow, V_75, %V₅₀ and %V₂₅. In their 40s, 50s and 60s, ES preserved better pulmonary function than CS consistently and the subjects who quit younger showed the more favourable function.

Conclusion Smoking impaired pulmonary function obviously and smoking cessation improved pulmonary function in Japanese people as Western. However earlier cessation was related to larger improvement, even 60s-quitter had certain effect.