Abstract
Objectives: This study aimed to investigate both the linear and non-linear associations between serum 25-hydroxyvitamin D [25(OH)D] levels and serum uric acid concentrations in Korean adults, with a particular focus on the vitamin D-insufficient range (<30 ng/mL), and to explore the potential metabolic implications of this relationship. Methods: Using data from the Korea National Health and Nutrition Examination Survey (KNHANES), we analyzed 10,864 adults aged 19 years and older. Serum vitamin D levels were categorized into quartiles (Q1-Q4), and their relationships with uric acid concentrations were examined using Pearson correlation, analysis of variance (ANOVA), and restricted cubic spline regression. Multivariate models were adjusted for potential confounders including age, sex, body mass index (BMI), kidney function, chronic disease status, and macronutrient intake. Results: In unadjusted analysis, a statistically significant but weak negative correlation was observed between serum 25(OH)D and uric acid levels (Pearson's r = -0.092, p < 0.001). However, in multivariate regression adjusting for confounders, a weak positive association emerged. Restricted cubic spline analysis revealed significant positive associations in the lower quartiles (Q1-Q3), with the strongest association in Q3 (β = 0.769, 95% CI: 0.34-1.19, p < 0.001). No significant association was observed in the highest quartile (Q4). Conclusions: Serum vitamin D and uric acid concentrations show a non-linear relationship, with a significant positive association within the vitamin D-insufficient range (<30 ng/mL). These findings provide new insights into the potential metabolic role of vitamin D and highlight the need for longitudinal and interventional studies to clarify causality and clinical significance.