Association between adult body size index and osteoarthritis/rheumatoid arthritis: a cross-sectional study

OBJECTIVE: Obesity is a recognized risk factor for arthritis. However, traditional anthropometric measures such as body mass index (BMI) have limitations in reflecting visceral fat distribution. Body size index for Adults (ABSI) is a new measure that combines waist circumference, height, and BMI to better predict obesity-related health risks. METHODS: A cross-sectional study was conducted using data from 36,856 participants (aged ≥18 years) in the 1999-2023 NHANES cycles. Participants were categorized into arthritis, RA, and OA groups based on self-reported physician-diagnosed conditions. Multivariate logistic regression, restricted cubic splines, and threshold effect analysis were performed to assess associations, adjusting for demographics, lifestyle factors, and comorbidities (e.g., hypertension, diabetes). RESULTS: ABSI was positively correlated with overall arthritis (OR = 2.54, 95%CI = 2.37-2.73, P < 0.001) and OA (OR = 1.15, 95%CI = 1.02-1.31, P = 0.024). But there was no correlation with RA (OR = 0.98, P = 0.832). ABSI had a threshold effect on arthritis (threshold = 7.435,P < 0.001) and OA (threshold = 8.015,P = 0.005). CONCLUSIONS: ABSI was a potential predictor of arthritis, especially OA, highlighting its potential for clinical risk stratification. The nonlinear association suggests different pathological mechanisms at higher ABSI thresholds, so longitudinal studies are necessary to verify causality and explore biological pathways.