Comparative analysis of pulmonary function in diverse ethnic adults living at low and high altitudes

High-altitude hypoxia poses substantial physiological challenges due to reduced atmospheric pressure and oxygen availability. While chronic exposure may induce compensatory adaptations in lung function, these responses likely vary by altitude and ethnicity. In China, both Han migrants and indigenous Tibetans reside at high elevations, offering a unique opportunity to explore ethnic-specific pulmonary adaptations. A retrospective, single-center observational study analyzed pulmonary function among adults residing at high (≥ 2,500 m) versus low (< 1,000 m) altitudes. Lung volumes, airflow, and diffusing capacity were compared between groups. Propensity score matching adjusted for baseline differences. Spearman correlation assessed associations between altitude and key parameters. Subgroup analyses were conducted by ethnicity and altitude strata. Multivariable linear regression was further applied for adjusting potential confounding. Among 10,112 participants (495 high-altitude, 9,617 low-altitude), high-altitude residents exhibited significantly higher forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC, maximum mid-expiratory flow (MMEF), inspiratory capacity (IC), total lung capacity (TLC), diffusing capacity of the lung for carbon monoxide (DLCO), and DLCO corrected for alveolar volume (DLCO/VA) (all P < 0.05), which remained significant after matching. Ethnic subgroup analysis showed high-altitude Tibetans had significantly greater FVC, IC, TLC, DLCO, and DLCO/VA than both low- and high-altitude Han individuals. The increase in DLCO exceeded that of FVC, particularly in Tibetans. Within the Han group, residence ≥ 2,500 m was associated with improved pulmonary metrics. Within 2,500–4,500 m, FVC (r = 0.163, P = 0.003) and DLCO (r = 0.287, P < 0.001) positively correlated with altitude. Above 4,500 m, DLCO remained correlated (r = 0.242, P = 0.020), whereas FVC plateaued (P > 0.05). Prolonged residence at high altitude is linked to increased lung volumes, airflow, and diffusing capacity. DLCO continued to rise beyond 4,500 m even as ventilatory adaptations plateaued, highlighting a sustained role of pulmonary diffusion in supporting oxygen uptake under chronic hypoxia.