Background and Aims: The significance of the systemic immune-inflammation index (SII) in assessing the inflammation condition has drawn considerable interest recently. Nevertheless, there has been no prior reporting on the correlation between serum vitamin C levels and SII. This study aimed to explore the relationship between serum vitamin C levels and SII score among adults in the United States. Methods and Results: The study utilized cross-sectional data from the 2003-2004 National Health and Nutrition Examination Survey (NHANES). Multivariable linear regression models were employed to determine the independent relationship between serum vitamin C levels and SII score. Subgroup analysis and interaction test were carried out as well. Fitted smoothing curves were also used to describe the nonlinear relationship. 4408 participants were enrolled and those in the higher serum vitamin C quartile exhibited a tendency towards a lower mean SII score. In the fully adjusted model, a negative relationship between serum vitamin C levels and SII score emerged (β= -50.05, 95% CI -74.47 to -25.62). Notably, participants in the highest serum vitamin C quartile demonstrated a 73.79-unit reduction in SII score (β = -73.79, 95% CI -102.29 to -40.55) compared to those in the lowest serum vitamin C quartile. Subgroup analysis and interaction tests revealed no dependence for the association of serum vitamin C and SII. Conclusion: Our findings indicate that serum vitamin C levels are negatively associated with SII score.

vitamin c, systemic immune-inflammation index, cross-sectional study