The Mediating Role of Body Mass Index in the Association of Socioeconomic Status With Hepatic Steatosis and Liver Fibrosis: A Cross-Sectional Study Based on NHANES 2021-2023.

Background: Socioeconomic status (SES) influences a wide range of health outcomes, including hepatic steatosis and liver fibrosis, which are increasingly concerning. The aim of the study was to investigate the association between SES and hepatic steatosis and liver fibrosis and examine the potential mediating effects of body mass index (BMI) in this association. Methods: We used the National Health and Nutrition Examination Survey (NHANES) 2021-2023 data to conduct a cross-sectional study. Occupation, insurance, family income level, and education level were employed as indicators of SES. Hepatic steatosis and liver fibrosis were quantified by controlled attenuation parameter (CAP) and liver stiffness measurement (LSM), respectively. Mediation analysis was used to estimate the direct and indirect associations of SES with hepatic steatosis and liver fibrosis through BMI after adjustment for potential confounders. Results: The study included 4455 participants. Compared to individuals with low SES, those with high SES had a lower risk of hepatic steatosis (odds ratios [OR] = 0.80, 95% CI: 0.69-0.94, p < 0.01) and liver fibrosis (OR = 0.77, 95% CI: 0.61-0.97, p=0.03). However, after adjusting for confounding factors, the associations were no longer statistically significant (hepatic steatosis: OR = 0.90, 95% CI: 0.75-1.08, p=0.25; liver fibrosis: OR = 0.87, 95% CI: 0.67-1.15, p=0.32). BMI differed significantly across SES grades (p=0.04). Restricted cubic spline analysis revealed a significant nonlinear positive association between BMI and hepatic steatosis (p < 0.01), and a linear positive association with liver fibrosis (p=0.11). Moreover, BMI accounted for 32.8% of the mediation effect between SES and hepatic steatosis and 18.2% of the mediation effect between SES and liver fibrosis. Conclusion: People with higher SES are less likely to develop hepatic steatosis and liver fibrosis, although the associations were attenuated after adjustment for confounding factors. SES might contribute to hepatic steatosis and liver fibrosis through the involvement of BMI.