Factors Associated With Metabolic Syndrome in Korean Older Adults: A Cross-Sectional Analysis of KNHANES VIII (2019-2021).

Background: Metabolic syndrome (MetS) is highly prevalent among older adults and substantially increases the risk of cardiovascular disease, type 2 diabetes, and mortality. Evidence regarding the independent contributions of lifestyle and nutritional factors to MetS in older populations remains inconclusive. This study examined factors associated with MetS among Korean older adults using nationally representative data within a complex-sample analytic framework. Methods: This cross-sectional study analyzed data from 3716 adults aged ≥ 65 years who participated in the Korea National Health and Nutrition Examination Survey (KNHANES) VIII (2019-2021). Survey weights, stratification, and clustering were incorporated to obtain nationally representative estimates. Complex-sample multivariable logistic regression was used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs). Chronic disease variables overlapping with MetS diagnostic components were excluded from the primary model to minimize overadjustment. Sensitivity analyses and interaction models using continuous BMI (per 5 kg/m² increase) were conducted. Results: The weighted prevalence of MetS was 38.0%. In fully adjusted models, BMI demonstrated the strongest association with MetS. Compared with individuals with normal BMI, underweight participants had higher odds of MetS (aOR = 7.72, 95% CI: 3.23-18.49), whereas obese participants had lower odds (aOR = 0.27, 95% CI: 0.23-0.32). Female sex was associated with lower odds of MetS (aOR = 0.69, 95% CI: 0.53-0.90). Smoking was positively associated with MetS (aOR = 1.34, 95% CI: 1.03-1.74). Insufficient energy intake was associated with lower odds of MetS (aOR = 0.78, 95% CI: 0.65-0.95), whereas excessive intake was not statistically significant. Physical activity adherence, alcohol consumption, and dietary fiber intake were not independently associated. A significant interaction between continuous BMI and smoking status was observed (aOR = 1.47, 95% CI: 1.05-2.06). Conclusions: Among Korean older adults, BMI was the dominant factor associated with MetS within a nationally representative complex-sample framework. The observed interaction between BMI and smoking suggests that adiposity and behavioral factors jointly influence metabolic risk in later life. These findings highlight the importance of integrated weight management and cardiometabolic risk reduction strategies in aging populations.