To investigate the association between daily dietary vitamin C intake and chronic kidney disease (CKD) prevalence among older adults and to develop a predictive nomogram model using NHANES 1999–2018 data.

Based on National Health and Nutrition Examination Survey 1999–2018, participants aged ≥60 years were included. Weighted multivariable logistic regression was used to assess the association between daily dietary vitamin C intake (excluding supplements) and CKD prevalence, with restricted cubic spline (RCS), subgroup, and sensitivity analyses performed to verify robustness. The sample was randomly divided into training and validation sets (7:3 ratio) to identify independent predictors and construct a nomogram model. Model performance was evaluated using the area under the curve (AUC), calibration plots, and decision curve analysis (DCA).

A total of 6540 participants aged ≥60 years were included. Daily dietary vitamin C intake was inversely associated with CKD prevalence after full adjustment (OR per 1 mg increase = 0.998, 95% CI: 0.997–0.999, P = 0.004). Compared with the lowest quartile, the highest quartile showed a significantly lower CKD prevalence (OR = 0.778, 95% CI: 0.610–0.992). Restricted cubic spline analysis indicated a linear relationship. The nomogram constructed based on independent predictors showed good discrimination (AUC = 0.737 in the training set and 0.715 in the validation set), good calibration, and favorable clinical utility within the threshold probability range of 0.09–0.81.

In this cross-sectional study of older adults, higher dietary vitamin C intake was inversely associated with CKD prevalence; the nomogram performed well and may aid risk assessment.