Vitamin C status across the spectrum of chronic kidney disease and healthy controls: a cross-sectional study

Background: Patients with chronic kidney disease (CKD) are at risk for vitamin C (VitC) deficiency. Objectives: We aimed to investigate VitC status and its determinants across the spectrum of CKD and healthy individuals. Methods: In this cross-sectional study, we measured plasma VitC concentrations (<10 μmol/L = deficient, 10‒35 μmol/L = inadequate) in 62 individuals on dialysis, 41 with CKD stage 4/5, 42 kidney transplant recipients (KTRs) (together: CKD population), and in 447 living kidney donors, and 385 healthy controls (together: healthy population). In the CKD population, we assessed VitC intake (<75 mg/d = inadequate) using 24-h dietary recalls. We measured VitC removal by hemodialysis. We investigated potential determinants of plasma VitC with linear regression in the CKD population and in the healthy population separately. Results: Median (Q1‒Q3) plasma VitC was highest in healthy controls [58 (43‒69) μmol/L, 14% inadequate/deficient], followed by kidney donors [50 (36‒66) μmol/L, 22% inadequate/deficient], KTR [37 (19‒46) μmol/L, 48% inadequate/deficient], dialysis [33 (19‒47) μmol/L, 58% inadequate/deficient], and CKD stage 4/5 [22 (14‒34) μmol/L, 80% inadequate/deficient]. Daily dietary VitC intake was similar in KTR [55.5 (33.5‒144.2) mg, 55% inadequate] and CKD stage 4/5 [53.0 (23.9‒142.0) mg, 56% inadequate], and higher in dialysis [113 (72‒209) mg, 26% inadequate] due to supplementation. VitC removal was 58 (27‒123) mg in conventional and 128 (97‒156) mg in nocturnal hemodialysis sessions. In the healthy population, estimated glomerular filtration rate was positively associated with plasma VitC [standardized β coefficient: 0.18 (0.08, 0.27), P < 0.001], independent of potential confounders. Conclusions: VitC inadequacy and deficiency are common in CKD. Inadequate intake and removal by dialysis may contribute. In healthy individuals estimated glomerular filtration rate was inversely associated with plasma VitC. Our findings highlight the importance of monitoring VitC status in CKD, and represent a potential target for intervention. Future research could evaluate the potential health effects of improving VitC status in CKD.