Objectives Chronic obstructive airway disease, which is characterised by airflow limitation, is a major burden on public health. Reductions in environmental pollution in the atmosphere and workplace and a decline in the prevalence of smoking over recent decades may have affected the prevalence of airflow limitation in Japan. The present epidemiological study aimed to evaluate trends in the prevalence of airflow limitation and in the influence of risk factors on airflow limitation in a Japanese community. Design Two serial cross-sectional surveys. Setting Data from the Hisayama Study, a population-based prospective study that has been longitudinally conducted since 1961. Participants A total of 1842 and 3033 residents aged ≥40 years with proper spirometric measurements participated in the 1967 and 2012 surveys, respectively. Main outcome measures Airflow limitation was defined as forced expiratory volume in 1 s/forced vital capacity <70% by spirometry. For each survey, the age-adjusted prevalence of airflow limitation was evaluated by sex. ORs and population attributable fractions of risk factors on the presence of airflow limitation were compared between surveys. Results The age-standardised prevalence of airflow limitation decreased from 1967 to 2012 in both sexes (from 26.3% to 16.1% in men and from 19.8% to 10.5% in women). Smoking was significantly associated with higher likelihood of airflow limitation in both surveys, although the magnitude of its influence was greater in 2012 than in 1967 (the multivariable-adjusted OR was 1.63 (95% CI 1.19 to 2.24) in 1967 and 2.26 (95% CI 1.72 to 2.99) in 2012; p=0.007 for heterogeneity). Accordingly, the population attributable fraction of smoking on airflow limitation was 33.5% in 2012, which was 1.5-fold higher than that in 1967 (21.1%). Conclusions The prevalence of airflow limitation was decreased over 45 years in Japan, but the influence of smoking on airflow limitation increased with time.
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