Association between vitamin D and inflammatory markers in the Chinese healthy adult population: a cross-sectional study

Background/Objectives: Vitamin D (VitD) plays an essential role in immune regulation, and growing evidence associates low VitD status with elevated systemic inflammation. However, large-scale, population-based evidence linking VitD status to systemic inflammatory markers in Chinese population are lacking. Objective: This study aimed to investigate the relationship between VitD levels and inflammatory markers in healthy Chinese individuals. Methods: This cross-sectional study was conducted at Zhejiang Provincial People’s Hospital (March 2019–August 2023) including a total of 51,521 participants. VitD levels were categorized according to serum 25-hydroxyvitamin D concentrations, and inflammatory markers were derived using established formulas. Primary outcome measures included the systemic immune-inflammation index (SII), platelet-to-lymphocyte ratio (PLR), and aggregate index of systemic inflammation (AISI). Associations between VitD levels and inflammatory markers were assessed using Spearman’s correlation and linear regression. Results: SII, PLR, and AISI were significantly higher among participants with VitD deficiency (P < 0.05). VitD levels were negatively correlated with SII (r = –0.063, P < 0.001), PLR (r = –0.095, P < 0.001), and AISI (r = –0.044, P < 0.001). In multivariable linear regression adjusting for age, sex, low-density lipoprotein cholesterol, triglycerides, uric acid, glucose, albumin, alanine transaminase, alkaline phosphatase, serum creatinine, and hemoglobin, VitD deficiency remained independently associated with SII, PLR, and AISI. Conclusion: VitD deficiency is an independent risk factor for elevated inflammatory markers, supporting a potential immunomodulatory role of VitD and highlighting the need for further research on its potential benefits in chronic disease prevention.