Prevalence of diabetes mellitus in individuals with airflow obstruction in a Japanese general population: The Yamagata-Takahata Study

Narrative review of current COPD status in Japan

Chronic obstructive pulmonary disease (COPD) causes morbidity and mortality worldwide. Due to the improvement in environmental sanitation and medical care, the general life span has increased in the past decades in Japan. However, many older patients with COPD develop a wide range of comorbidities, and the impairments in the activities of daily living result in frailty and increase social and economic burdens. Population-based studies have shown that the prevalence of COPD is approximately 10% among subjects aged ≥40 years, but more than 80% of COPD patients are underdiagnosed. The Ministry of Health, Labour, and Welfare in Japan proposed the National Health Promotion in the 21st century, termed Health Japan 21 (the second term), in 2013 to prevent the onset and progression of noncommunicable diseases (NCDs), including COPD. The government, medical society, and community have been attempting to increase the recognition of COPD and promote smoking cessation. Additionally, Japanese cohorts have revealed distinct clinical features in Japanese patients with COPD, including lower rates of patient-reported exacerbations, less frequent coexisting cardiovascular disease and metabolic syndrome, and lower use of inhaled corticosteroids in Japan compared to the Western countries. Moreover, the poor adherence to inhaled medications is found in approximately 20% of subjects, and rehabilitation is performed in 26% of hospitalized patients with COPD. Therefore, more efforts should be made to improve adherence and access to pulmonary rehabilitation. Overall, Japanese COPD patients share common clinical and social features with COPD patients in other countries. Further international corroboration may help establish better comprehensive management of the disease.

Genetic Correlation and Bidirectional Causal Association Between Type 2 Diabetes and Pulmonary Function

BACKGROUND

Observational studies have shown possible bidirectional association between type 2 diabetes (T2D) and pulmonary function, but the causality is not well defined. The purpose of this study is to investigate genetic correlation and causal relationship of T2D and glycemic traits with pulmonary function.

METHODS

By leveraging summary statistics from large-scale genome-wide association studies, linkage disequilibrium score regression was first implemented to quantify genetic correlations between T2D, glycemic traits, and several spirometry indices. Then both univariable and multivariable Mendelian randomization analyses along with multiple pleiotropy-robust methods were performed in two directions to assess the causal nature of these relationships.

RESULTS

Forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) showed significant genetic correlations with T2D and fasting insulin levels and suggestive genetic correlations with fasting glucose and hemoglobin A1c. In Mendelian randomization analyses, genetically predicted higher FEV1 (OR = 0.77; 95% CI = 0.63, 0.94) and FVC (OR = 0.82; 95% CI = 0.68, 0.99) were significantly associated with lower risk of T2D. Conversely, genetic predisposition to higher risk of T2D exhibited strong association with reduced FEV1 (beta = -0.062; 95% CI = -0.100, -0.024) and FEV1 (beta = -0.088; 95% CI = -0.126, -0.050) and increased FEV1/FVC ratio (beta = 0.045; 95% CI = 0.012, 0.078). We also found a suggestive causal effect of fasting glucose on pulmonary function and of pulmonary function on fasting insulin and proinsulin.

CONCLUSIONS

The present study provided supportive evidence for genetic correlation and bidirectional causal association between T2D and pulmonary function. Further studies are warranted to clarify possible mechanisms related to lung dysfunction and T2D, thus offering a new strategy for the management of the two comorbid diseases.

Bidirectional relationship between diabetes and pulmonary function: a systematic review and meta-analysis

AIM

Evidence of the lungs being a target organ of diabetes-related pathophysiology is increasing, and decreased pulmonary function increases the risk of diabetes after adjusting for demographic and metabolic factors. This systematic review and meta-analysis evaluates the bidirectional relationship between diabetes and pulmonary function.

METHODS

MEDLINE, Embase, The Cochrane Library and Web of Science databases were searched, and all studies describing this bidirectional relationship were identified. Two reviewers independently extracted study characteristics and assessed the risk of bias.

RESULTS

A total of 93 studies were included in the meta-analysis. The pooled weighted mean difference (WMD) between diabetes patients and non-diabetic participants for forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) were -5.65% and -5.91%, respectively, of predicted values. Diabetes-related microvascular complications and poor glycaemic control were associated with poorer pulmonary function in those with diabetes. In addition, diabetes was associated with a restrictive spirometry pattern (RSP) in both cross-sectional studies [odds ratio (OR): 2.88, 95% confidence interval (CI): 2.18-3.81, I² = 0.0%] and prospective cohort studies [hazard ratio (HR): 1.57, 95% CI: 1.04-2.36]. In five longitudinal studies, the conclusions were inconsistent as to whether or not diabetes accelerates pulmonary function decline. However, every 10% decrease in baseline predicted FVC value was associated with a 13% higher risk of incident diabetes (HR: 1.13, 95% CI: 1.09-1.17, I² = 0.0%).

CONCLUSION

There is a bidirectional relationship between diabetes and pulmonary function. However, further investigations into whether dynamic changes in glycaemic levels before and shortly after diabetes onset mediate the deleterious effects on pulmonary function, or vice versa, are now required.

Impact of reduced pulmonary function in the Japanese general population: Lessons from the Yamagata-Takahata study

Regional epidemiological studies for respiratory diseases have been rarely performed in Japan, because spirometry is not regularly conducted in the standard annual health checks. The Yamagata-Takahata Study is an epidemiological study utilizing regional characteristics based on the 21st Century Centers of Excellence (COE) Program and the Global COE Program. Spirometric examination and other specific measurements via blood sampling were performed for the study participants in annual health check-ups held in Takahata, a town in Yamagata Prefecture. The Yamagata-Takahata Study revealed the impact of cigarette smoking habit on pulmonary function, the impact of reduced pulmonary function on mortality, and the situation regarding COPD comorbidities in Japan. Additionally, the study identified biomarkers of decline in pulmonary function among active smokers, and the risk factors for respiratory mortality in Japan. In this review, we summarize the findings of the Yamagata-Takahata study regarding the association between lower pulmonary function and the clinical characteristics of a Japanese general population.