TOPLINE:

Vitamin C deficiency and inadequacy were common in patients with chronic kidney disease (CKD), particularly those with CKD stage 4 or 5 and those undergoing dialysis. Even in otherwise healthy individuals, poorer kidney function was associated with lower plasma vitamin C levels.

METHODOLOGY:

• Researchers conducted a cross-sectional study to assess vitamin C status and its determinants in patients with CKD (62 undergoing dialysis, 41 with CKD stage 4 or 5, and 42 kidney transplant recipients) and healthy individuals (447 living kidney donors and 385 healthy control individuals).
• Plasma vitamin C levels were measured using high-performance liquid chromatography and categorised as adequate (> 35 μmol/L), inadequate (> 10-35 μmol/L), or deficient (≤ 10 μmol/L).
• In the CKD group, vitamin C intake was evaluated using 24-hour dietary recalls conducted by a dietitian, with intake below 75 mg/d being considered inadequate.
• Vitamin C clearance in patients on dialysis was assessed by sampling blood and dialysate at multiple timepoints during a session.

TAKEAWAY:

• Median plasma vitamin C levels were highest in healthy control individuals (58 μmol/L), followed by kidney donors (50 μmol/L), kidney transplant recipients (37 μmol/L), patients undergoing dialysis (33 μmol/L), and those with CKD stage 4 or 5 (22 μmol/L); over half of patients with CKD had inadequate or deficient levels — most notably those with stage 4 or 5 disease (80%) and those undergoing dialysis (58%).
• Inadequate daily vitamin C intake was found in 69% of patients on dialysis (despite supplementation), 56% of those with CKD stage 4 or 5, and 55% of kidney transplant recipients.
• In the healthy population, the estimated glomerular filtration rate was positively associated with plasma vitamin C levels (P < .001), independent of potential confounders.
• Finally, vitamin C clearance in patients on haemodialysis was higher during nocturnal in-centre haemodialysis sessions than during conventional haemodialysis sessions (128 vs 58 mg; P = .04).

IN PRACTICE:

"Our findings highlight the importance of monitoring vitamin C status in individuals with impaired kidney function, and suggest opportunities for targeted interventions to improve vitamin C status," the authors wrote.

SOURCE:

This study was led by Caecilia S.E. Doorenbos, MD, University Medical Center Groningen, Groningen, Netherlands. It was published online on September 10, 2025, in The American Journal of Clinical Nutrition.

LIMITATIONS:

This study used single 24-hour dietary recalls, which may have limited the accuracy of dietary intake data. Only limited data on dietary intake were available for the healthy population. Additionally, the observational nature of the study prevented the establishment of causality and may have resulted in residual confounding.

DISCLOSURES:

This study was funded by the Dialysis Center Groningen. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.