Age-related factors associated with preserved ratio impaired spirometry: The Tohoku medical Megabank project community-based cohort study

Background: Preserved ratio impaired spirometry (PRISm), defined as a forced expiratory volume in 1 s (FEV₁) to forced vital capacity (FVC) ratio ≥0.70 and a predicted FEV₁ <80 %, is associated with increased morbidity and mortality. However, determinants of PRISm, particularly in younger populations, remain poorly characterised. We aimed to address this knowledge gap. Methods: We conducted a cross-sectional analysis of 12,350 participants from a Japanese community-based cohort using data from the Tohoku Medical Megabank Project. Participants underwent spirometry, blood pressure measurement, laboratory testing, and completed standardised questionnaires. Multivariate logistic regression was used to identify factors associated with PRISm across three age groups: 20–39, 40–59, and ≥60 years. Interactions between age groups and other explanatory variables were assessed. Results: In the 20–39-year group, PRISm was independently associated with being men, diabetes mellitus, hypothyroidism, and low body mass index (BMI <18.5 kg/m²), and inversely associated with age. Among participants aged ≥60 years, PRISm was significantly associated with increasing age, overweight status (BMI ≥25.0–<30.0 kg/m²), being men, current smoking, hypertension, diabetes mellitus, bronchial asthma, elevated eosinophil counts (≥300 cells/μL), and birth weight ≥2000–<2500 g. Significant interactions were observed between age and BMI, bronchial asthma, and thyroid dysfunction. Conclusions: Our findings indicate that PRISm in younger adults is associated with hypothyroidism and underweight status, whereas in older adults, it is more closely related to constitutional and lifestyle-related factors. These results highlight the heterogeneity of PRISm and indicate that its pathophysiology and optimal management may vary by age group.