ObjectiveTo investigate the correlation between different forms of serum vitamin D levels and liver fibrosis in patients with metabolic dysfunction-associated fatty liver disease (MAFLD).MethodsData from the National Health and Nutrition Examination Survey in 2021–2023 were analyzed. Logistic regression models were used to evaluate the relationship between serum total vitamin D, 25(OH)D₃ levels, and liver fibrosis in the MAFLD patients.ResultsA total of 2 628 patients were included. There were significant differences between MAFLD patients with liver fibrosis and those without fibrosis in age, smoking history, waist circumference, body mass index, high-density lipoprotein cholesterol, total cholesterol, fasting plasma glucose, hypertension history, vitamin D, and 25(OH)D₃ levels (P<0.05). Logistic regression analysis revealed that compared to the low total serum vitamin D group (11.2-61.8 nmol/L), MAFLD patients with high total vitamin D levels (89.1 nmol/L<vitamin D≤290 nmol/L) exhibited a 22% reduced risk of liver fibrosis (OR=0.78, 95%CI 0.64-0.94, P=0.015). Similarly, compared to the low 25(OH)D₃ group (4.1-57.0 nmol/L), those with high 25(OH)D₃ level [84.7 nmol/L<25(OH)D₃≤288 nmol/L] showed a 23% lower risk of liver fibrosis (OR=0.77, 95%CI 0.62-0.95, P=0.021). After adjusting for covariates, high total vitamin D levels remained significantly associated with reduced liver fibrosis risk (OR=0.63, 95%CI 0.42-0.94, P=0.036).ConclusionsElevated serum total vitamin D and 25(OH)D₃ levels are protective factors against early liver fibrosis in MAFLD patients.