Mendelian Randomization Analysis of Systemic Iron Status and Risk of Metabolic Dysfunction-Associated Steatotic Liver Disease.

Objective: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a global public health crisis, progressing to hepatic cirrhosis and hepatocellular carcinoma. This study investigated the causal role of systemic iron status in MASLD progression. Methods: A two-sample Mendelian randomization (MR) design was implemented, with genetic variants serving as instrumental variables for four core systemic iron biomarkers. Outcome data for hepatic steatosis (8785 cases; 912,105 controls) and hepatic fibrosis/cirrhosis (3798 cases; 904,599 controls) were extracted from the FinnGen and UK Biobank databases. Multiple complementary MR methodologies and three instrumental variable selection strategies were applied to ensure robust causal inference. Results: Genetically predicted higher serum iron (odds ratio, OR: 1.42, 95% confidence interval, 95% CI: 1.34, 1.50), ferritin (OR: 1.84, 95% CI: 1.55, 2.18), and transferrin saturation (TfSat, OR: 1.24, 95% CI: 1.19, 1.30), together with lower total iron-binding capacity (TIBC, OR: 0.81, 95% CI: 0.77, 0.85), were significantly associated with increased hepatic steatosis risk (p < 0.00625). Similar associations were observed for hepatic fibrosis/cirrhosis: serum iron (OR: 1.66, 95% CI: 1.29, 2.14), ferritin (OR: 2.52, 95% CI: 1.52, 4.18), TfSat (OR: 1.40, 95% CI: 1.19, 1.63), and reduced TIBC (OR: 0.70, 95% CI: 0.60, 0.81). MR-Bayesian model averaging prioritized serum iron (MIP: 0.85, θ^MACE: 0.295; PP: 0.725; θ^λ: 0.344) as the top-ranked factors for steatosis and TIBC (MIP: 0.604, θ^MACE: -0.240; PP: 0.476, θ^λ: -0.358) for fibrosis/cirrhosis. Conclusions: Elevated systemic iron status causally drives MASLD onset and progression, highlighting iron homeostasis and ferroptosis as potential targets for prevention and clinical management.