Effects of smoking and age on chronic obstructive pulmonary disease in Japan

Background: The Global Initiative for Chronic Obstructive Lung Disease guidelines recommended a forced expiratory volume at one second per forced vital capacity as a standard diagnostic criterion of chronic obstructive pulmonary disease (COPD). A few reports on the risk factors of COPD have used the standard diagnostic criteria. In our study, the effects of age and smoking on COPD in Japan under the standard diagnosis criteria were evaluated. Methods: Subjects were 11,460 participants aged 25-74 years during health check-ups including spirometry at the Toyota Community Medical Center in Japan. Logistic regression analyses with or without COPD as a dependent variable and age as an independent variable were conducted among non-smokers. The ratio of the observed number of COPD cases in former and current smokers to the number expected for non-smokers with the same distribution of age (O/E) was calculated. Results: The proportion of males incurring COPD significantly increased with age, and the O/E for former and current male smokers was significantly higher than one, i.e., O/E (95% confidence interval) for current smokers with a Brinkman Index of <400, 400-799, and 800+ were 3.10 (2.00-4.81), 2.78 (2.05-3.73), and 4.76 (3.65-6.19), respectively. Among females, the O/E for current smokers with a Brinkman Index of <400, and 400-799 were significantly higher than one. Conclusion: Age and smoking were shown to constitute strong risk factors for COPD under the standard diagnostic criteria.