Physical activity, sedentary behavior, and metabolic syndrome in adults with arthritis: cross-sectional and Mendelian randomization analysis.

This study examined the relationship between moderate-to-vigorous physical activity (MVPA), sedentary behavior (SB), and metabolic syndrome, employing both cross-sectional and Mendelian randomization methods to enhance causal inference. The cross-sectional analysis included adults aged 20 years and older with arthritis (n=4,227) from the National Health and Nutrition Examination Survey and assessed the associations between MVPA, SB, and metabolic syndrome. Mendelian randomization analysis used genome-wide association studies to validate causal relationships, employing instrumental variables selected from single nucleotide polymorphisms linked to accelerometer-based physical activity (fraction of time with accelerations >425 milli-gravities) and SB. The primary Mendelian randomization methods included inverse variance weighting and Bayesian Weighted Mendelian Randomization. Sensitivity analyses, including Mendelian Randomization-Egger intercept test, the weighted median method, and Mendelian Randomization Pleiotropy RESidual Sum and Outlier, were conducted to ensure result robustness. Cross-sectional analysis revealed a significant association between higher levels of MVPA and reduced SB with a lower prevalence of metabolic syndrome. Participants in the high MVPA/low SB group demonstrated lower odds of metabolic syndrome (odds ratio [OR], 0.40; 95% confidence interval [CI], 0.29-0.56), hypertension (OR, 0.55; 95% CI, 0.40-0.75), fasting glucose (OR, 0.52; 95% CI, 0.35-0.77), and waist circumference (OR, 0.34; 95% CI, 0.22-0.54). Mendelian randomization analysis confirmed a causal relationship, showing that physical activity decreases risk factors for metabolic syndrome, while SB exacerbates them. This study emphasizes the critical roles of regular physical activity and reduced SB in mitigating the risk of metabolic syndrome, especially among older adults with arthritis.