U-shaped relationship between serum vitamin C concentration and prevalence of kidney stones:a cross-sectional study from NHANES

Background The relationship between vitamin C levels and the risk of kidney stone formation remains controversial. This study aimed to investigate the association between serum vitamin C concentration and renal calculi occurrence. Methods A cross-sectional analysis was conducted using data from the 2017–2018 National Health and Nutrition Examination Survey, comprising 4932 participants. Serum vitamin C concentrations were measured by ultra performance liquid chromatography. The prevalence of kidney stones among participants was determined through self-reported questionnaires. Segmented regression analysis identified a serum vitamin C threshold value of 1.69 mg/dL, the significance of which was confirmed by a log-likelihood ratio test. Subsequently, three logistic regression models were constructed to examine the effects of excess (≥ 1.69 mg/dL) versus non-excess serum vitamin C on kidney stones. Stratified analyses were conducted to evaluate the applicability of these models across different populations. Results The prevalence of kidney stones among participants was 10.22%. A U-shaped relationship was observed between serum vitamin C concentration and kidney stone prevalence, with a threshold identified at 1.69 mg/dL. Below this threshold, each unit increase in serum vitamin C concentration decreased kidney stone incidence by 29%. Conversely, above this threshold, kidney stone prevalence was positively correlated with serum vitamin C concentrations. Conclusions This study identified a nonlinear relationship between serum vitamin C concentration and kidney stone risk, indicating that both excessively high and low serum vitamin C levels are associated with increased risk. These findings underscore the importance of maintaining appropriate serum vitamin C levels for kidney stone prevention; however, further clinical studies are required to validate our conclusions.