Discussion
Our study showed that the prevalence of COPD has gradually increased from 7.9% in 2009 to 16.7% in 2018. Trends from 2008 to 2017 revealed a general decrease in mortality rates across the population. However, participants with COPD consistently had higher mortality rates, both crude and age-standardised, than those without COPD. Moreover, the comparative mortality risks indicated that the overall mortality, including specific causes such as neoplasms and respiratory diseases, was significantly higher in the COPD group. The incidence rate and risk of mortality due to lung cancer and lower respiratory diseases, such as asthma and bronchiectasis, were particularly higher in the COPD group, underscoring the severe impact of COPD on health outcomes.
The first significant observation in this study pertained to the prevalence of COPD in Korea and its trends in the entire population. We found a prevalence of 16.7%, which notably exceeds the global prevalence of 10.3% reported by the Global Initiative for Chronic Obstructive Lung Disease.3 Previous research on the prevalence of COPD in Korea, based on the KNHANES, indicated rates ranging from 11.5% to 13.6%.7 13 14 However, these studies were cross-sectional. It is also possible that the COPD prevalence observed in our study might have been somewhat overestimated compared with certain Korean studies that used ICD-10 codes (J43 and J44) employed by the Korea Health Insurance Review and Assessment Service to evaluate appropriate COPD management. Nonetheless, the ICD-10 code range (J41–J44) we employed is not a significant concern, as it is a definition commonly used in other studies, including previous systematic reviews.15 16
The present study, which encompassed the entire Korean population, provides a more comprehensive and detailed reflection of the COPD situation in Korea. A contributing factor to this higher prevalence rate and rising trend could be various reasons, including rapid urbanisation, increased exposure to fine dust particles, cigarette smoking and increased life expectancy.17 Ageing is a recognised risk factor for COPD development,7 18 19 as it is associated with declining lung function and physiological changes, such as cellular senescence, genomic instability and mitochondrial dysfunction.18 20 In fact, the proportion of individuals aged 60 years or older consistently increased in this population, rising from 32.8% in 2008 to 38.5% in 2017 (online supplemental table 1). These demographic shifts were significantly correlated with the onset of COPD, as our findings suggest; approximately 62.4% of the COPD group were aged 60 years or older, compared with 33% in the non-COPD group.
Moreover, since 2013, Korea has been conducting assessments for appropriate COPD treatment and management annually for medical institutions. Efforts have also been made to enhance public awareness and early detection of COPD, which has been under-diagnosed and under-treated compared with other chronic diseases, through collaborative initiatives between academic societies and the government.21 22 These initiatives have led to increased awareness and diagnosis of COPD, which seems to be reflected in prevalence.
A notable finding of this study was the trend in COPD mortality in Korea. The age-standardised mortality rate of COPD was 1830 per 100 000 people in 2008 and has steadily decreased since then to 1046 per 100 000 people in 2017. This downward trend aligns with that reported by previous studies23–25 and likely results from improved COPD management and smoking cessation efforts.3 Particularly, various public health projects aimed at improving the early detection and management of patients with COPD, as discussed in the preceding paragraph, may have positively influenced the mortality rate. These projects involve raising awareness about COPD among the general public, developing educational materials targeting high-risk populations and primary care physicians, emphasising the significance of inhaler treatment and managing COPD according to clinical practice guidelines.22
Additionally, the gradually improving smoking rate in Korea may also correlate with the decrease in mortality among patients with COPD. Cigarette smoking is known as the most common and well-documented risk factor for COPD. Although we could not directly confirm the smoking rate in the current data, national statistics on cigarette smoking rates in Korea indicated a significant decrease, especially from 47.8% to 38.1% among male adults during the study period.26 Smoking cessation is the most effective method to prevent COPD, slow its progression, minimise acute exacerbations and reduce mortality. However, the COPD mortality rate remains two times as high compared with that of the overall population in Korea. Despite being less recognised than common fatal diseases like cancer, heart disease and stroke, COPD poses a significant and persistent public health concern. Therefore, reducing the risk of developing COPD and improving outcomes for those already living with the disease is crucial. This emphasises the need for effective COPD prevention and management strategies.
Another finding of this study was that patients with COPD had a significantly higher mortality risk across various health conditions than those without COPD. Specifically, mortality due to neoplasms and respiratory diseases was notably higher in the COPD group. This finding suggests that COPD may directly exacerbate these conditions or weaken the body’s resilience. Similarly, the TORCH study indicated that 35% of deaths among patients with COPD were due to chronic pulmonary disease.27 Additionally, a Korean study reported a 17.5% mortality rate due to chronic lower respiratory disease in patients with COPD.9 In the present study, the risk of mortality due to respiratory diseases was more than double, and the risk of mortality due to lower respiratory diseases was 16 times higher. This can be linked to mucosal damage from smoking or other environmental irritants, which makes lungs of individuals with COPD more susceptible to infections and exacerbations due to bacterial pathogens or viruses, particularly lower respiratory infections.28 29 Collectively, these findings highlight the severe impact of COPD on health outcomes. They call for a more nuanced understanding of the disease’s progression and its interactions with other health conditions. This, in turn, necessitates a more integrated approach to managing COPD, addressing not only the primary disease but also the comprehensive health of patients. This involves vigilant monitoring and prevention of serious comorbidities.
Despite these clinical implications, this study had several limitations. First, this study did not define COPD based on pulmonary function tests. COPD is defined as airflow limitation in pulmonary lung function, indicated by a post-bronchodilator forced expiratory volume in 1 s/forced vital capacity ratio of <0.70.3 Instead, the study relied on ICD-10 codes (J41–J44) to identify COPD cases. Nonetheless, efforts were made to minimise inaccuracies by including patients with two or more ICD-10 codes or those hospitalised for COPD. However, this approach may not capture the full spectrum of the disease, particularly mild cases or individuals not seeking medical care. Another limitation is the higher prevalence of COPD reported among women in this study. This finding contrasts with most other studies in which the prevalence of COPD was typically higher in men. This discrepancy might be due to differential healthcare utilisation patterns, as reports suggest that women use hospitals more than men.30 31 Similar to this study, previous study also showed a higher prevalence of COPD in women.32 It is believed that these results may have occurred because women live longer than men in the Korean population (online supplemental table 1) and their medical utilisation rate is high. This difference in healthcare-seeking behaviours could have influenced the study’s findings, potentially leading to an overestimation of the prevalence of COPD among women. Finally, our analysis did not fully encompass a range of influential factors, such as socioeconomic status, smoking habits, occupational exposure and lifestyle choices. Specifically, we collected smoking-related variables from individuals who underwent national health checkups in the current or previous year to ascertain information about their smoking habits. However, despite these efforts, the smoking status of more than half of the subjects could not be confirmed based on the 2017 data. These factors play crucial roles in determining the prevalence and severity of COPD. Consequently, the absence of these considerations in our study is a limitation, as they are essential for a comprehensive understanding of the impact of COPD. Therefore, although our findings contribute significantly to the existing body of knowledge, they should be interpreted with an awareness of these unaddressed variables.
In conclusion, our study indicates a gradual increase in COPD prevalence over the past decade. This rise may be attributed not only to an increase in the population exposed to COPD risk factors but also to improvements in diagnosing and treating previously overlooked cases of COPD. Furthermore, we found that both overall (all-cause) and cause-specific mortality rates were significantly higher in the COPD group compared with the non-COPD group. However, the gap in mortality between the COPD and non-COPD groups has been gradually narrowing in Korea, reflecting ongoing efforts to enhance COPD management. However, there is still a need for effective prevention and management strategies to reduce the personal and socioeconomic burdens associated with COPD exacerbations. A further longitudinal cohort study is necessary to further validate our findings and evaluate the actual level of treatment and management after the diagnosis of COPD, considering various potential confounding factors that were not addressed in this study.