Association of metabolic syndrome and its severity with liver fibrosis: a cross-sectional study based on NHANES 2017–March 2020, 2021–2023

Liver fibrosis has a high global prevalence and poses a substantial public health burden with significant implications for individual health and healthcare systems. To guide preventive and therapeutic approaches for liver fibrosis, this analysis explored the relationship between MetS, its severity grades, and hepatic fibrotic changes. Data for this cross-sectional investigation were obtained from NHANES cycles spanning 2017–March 2020, 2021–2023. Weighted logistic regression models were employed to evaluate the associations of MetS and its severity with liver fibrosis. Potential nonlinear dose–response patterns were assessed through restricted cubic spline modeling. Subgroup analyses were performed to identify effect modification across population characteristics and to assess interaction effects. The stability of the results was verified through sensitivity analyses. A total of 3,940 participants were included, with a weighted prevalence of liver fibrosis of 10.6%. A significant positive relationship between MetS and liver fibrosis emerged from weighted logistic regression (OR = 2.225, 95% CI: 1.311–3.775). Increasing severity of MetS was associated with progressively elevated risk of liver fibrosis, with the highest risk observed among individuals in the most severe category (OR = 5.399, 95% CI: 2.527–11.54). A statistically significant nonlinear relationship between MetS severity and liver fibrosis was identified through restricted cubic spline modeling (P for nonlinear = 0.016). Subgroup analyses indicated that the association between MetS and liver fibrosis appeared stronger among participants who smoked or consumed alcohol. Individuals with MetS exhibited a higher risk of liver fibrosis compared with those without MetS, and this risk increased progressively with greater disease severity. These findings elucidate the association pattern between MetS, its severity, and liver fibrosis risk, providing population-level evidence to inform liver disease prevention and control strategies.