**Background:** Oxidative stress, a state where pro-oxidants overwhelm antioxidant capacity, can damage biomacromolecules and is implicated in airway pathologies such as idiopathic pulmonary fibrosis and chronic obstructive pulmonary disease. The oxidative balance (OB) scoring system semi-quantitatively measures oxidative stress based on nutritional and lifestyle factors. Despite known links between oxidative imbalance and lung disease, the association in the general population has received little attention. This study aimed to investigate the relationship between OB scores and spirometry results in a representative sample of Korean adults.
**Methods:** Data were extracted from the 2013–2019 Korean National Health and Nutrition Examination Survey (KNHANES), a nationwide, population-based survey using stratified, multistage probability sampling. From 20,909 subjects aged 40–79 years with pulmonary function test data, 17,368 individuals with available OB scores were included. Pre-bronchodilator spirometry measured FEV1 and FVC as percentages of predicted values. OB scores were calculated from 10 components: 5 pro-oxidant factors (polyunsaturated fatty acids, n-6 fatty acids, smoking, alcohol, obesity) and 5 antioxidant factors (carotene, retinol, vitamin C, n-3 fatty acids, physical activity). Dietary intake was assessed by 24-hour recall, and lifestyle factors by self-administered questionnaire. Each component was scored 0–3, with a maximum possible score of 30 (higher scores indicating antioxidant predominance). Multivariable logistic regression adjusted for age, sex, economic status, and comorbidities (hypertension, type 2 diabetes, lung disease) estimated odds ratios (ORs) for reduced lung function (<80% predicted) per 1-point decrease in OB score. Linear trends across severity groups were tested.
**Key Results:** The median OB score was 17.0 (IQR 15–19). Males (median 16 vs. 18 in females, p<0.001), low-income subjects (median 17 vs. 17 in high-income, p<0.001), and those with hypertension (median 16 vs. 17, p<0.001), type 2 diabetes (median 16 vs. 17, p<0.001), or reduced lung function had significantly lower OB scores. The association between oxidative imbalance and reduced lung function was stronger for FVC than FEV1: overall OR per 1-point decrease in OB score was 1.06 (95% CI 1.04–1.07, p<0.001) for FVC and 1.03 (95% CI 1.02–1.04, p<0.001) for FEV1. Subgroup analyses showed consistent associations across most groups, except for FEV1 in females (OR 1.00, 95% CI 0.98–1.02, p=0.762) and in patients with lung disease (OR 1.03, 95% CI 0.99–1.07, p=0.092). A significant linear relationship was observed between severity of lung function impairment and OB scores: for FEV1, OB scores were 17.02 (≥80% predicted), 16.73 (50–79%), and 16.45 (<50%); for FVC, scores were 17.06, 16.55, and 16.04, respectively (p for trend <0.001 for both).
**Clinical Implications:** This first epidemiologic study in a general population demonstrates that oxidative imbalance is associated with reduced pulmonary function, particularly FVC, suggesting that oxidative stress may impair lung capacity before overt respiratory disease develops. The findings support the potential for primary prevention strategies targeting modifiable pro-oxidant and antioxidant factors—such as smoking cessation, alcohol moderation, weight management, and dietary improvements—to preserve lung health. However, the cross-sectional design precludes causal inference, and longitudinal studies are needed. Limitations include recall bias in dietary assessment, lack of endogenous antioxidant measurement, and limited generalizability to non-Korean populations. Replication with biochemical oxidative stress markers and interventional studies are warranted.