Associations between urinary iodine concentration and metabolically dysfunction-associated steatotic liver disease and advanced liver fibrosis in US adults: Evidence from the NHANES database 2001–2020

Given the potential significance of iodine in the development of metabolic dysfunction-associated steatotic liver disease (MASLD), this study aims to investigate the associations between urine iodine concentration (UIC), MASLD, and advanced liver fibrosis. Using data from the National Health and Nutrition Examination Survey. Logistic analysis generated odds ratios (OR) and 95% confidence intervals (CI) to assess the impact of iodine status. Restricted cubic spline (RCS) functions were applied to detect nonlinear relationships between UIC and MASLD/advanced liver fibrosis. Receiver operating characteristic curves evaluated UIC's predictive capacity. The robustness of the findings was assessed via sensitivity analyses, and differences across populations were examined through subgroup analyses. Following comprehensive adjustments, lower UIC individuals exhibited lower odds for MASLD (OR 0.77; 95% CI: 0.61-0.99) and advanced liver fibrosis (OR 0.58; 95% CI: 0.38-0.89) in comparison to those with normal UIC. Stratifying by UIC quartiles, the third quartiles (OR 1.56; 95% CI: 1.18-2.07) and fourth quartiles (OR 1.58; 95% CI: 1.23-2.00) were associated with increased MASLD risk, a finding further confirmed in sensitivity analyses. RCS analysis revealed a nonlinear relationship between UIC concentration and the risk of MASLD. Subgroup analyses did not reveal any heterogeneity in this study. A low urinary iodine concentration is associated with a diminished risk of MASLD and advanced liver fibrosis, whereas elevated iodine levels were significantly linked to an increased MASLD risk. Longitudinal and experimental studies are necessary to elucidate causality and guide clinical recommendations.