Do Not Ignore Vitamin C Management in CKD – Renal and Urology News

Vitamin C, like many other nutrients in CKD, has been associated with a fear of increased levels causing harm. This is primarily due to vitamin C’s role in oxalate formation, which can lead to kidney stones, increased buildup of oxalates in bones and soft tissues, or even lead to kidney damage. While it is important to be aware of potential harm from nutrients, oxalate nephropathy is rare, with an estimated prevalence of 3.6%.¹

Studies have found low vitamin C levels in 64% of those on hemodialysis (HD) and peritoneal dialysis (PD).²  In another study, 52% of those prescribed vitamin C supplements still had low vitamin C levels.³ Low vitamin C levels are also associated with increased mortality,⁴ endothelial dysfunction, increased oxidative stress and cardiovascular disease.⁵  Based on this, it would seem that increasing intake of vitamin C can play a beneficial role in improving outcomes for those with CKD.

Guidelines from the Kidney Disease Outcomes Quality Initiative (KDOQI) suggest a Recommended Dietary Allowance (RDA) of vitamin C of 90 mg/d for men and 75 mg/d for women for those with CKD stages 1-5 and on dialysis or following kidney transplantation.⁶ The KDOQI guidelines point out, however, that there are limited studies to clarify vitamin C needs in those with CKD at any stage. Therefore, individualized recommendations are the most appropriate clinical approach for vitamin C recommendations in those with CKD at this time.³

Clinicians can consider the following to make an individualized vitamin C recommendation:

• Remember that the RDA recommendations are appropriate for healthy individuals only, and specifically state that alternate recommendations are more appropriate for those on HD or PD.⁸
• Consider dialysis losses (on average 66 mg per HD treatment and 29 mg per PD session), although some studies have estimated vitamin C losses to be as high as 300 mg per HD treatment.⁹
• Consider current patient intake (average intake for HD patients was found to be 66 mg/day).¹⁰
• Research shows both increased and decreased reabsorption from the kidneys in CKD.⁹
• Patients with CKD frequently have increased inflammation, anemia, periodontal disease, and secondary hyperparathyroidism, which may increase vitamin C need.⁴
• Consider patients’ history of kidney stones or other oxalate- related issues, such as from gastric bypass, or poor fat digestion.¹¹
• If a deficiency is found, doses greater than the RDA are needed to replenish vitamin C.  Also keep in mind that a dose greater 500 mg is typically not absorbed, so an adjustment of dosing may be needed.¹²

Doses from studies that can help guide clinicians in their recommendations:

Treatment for deficiency (in individuals without CKD) is started high and then titrated down:¹³

• 1-2g/d for 2-3 days in divided doses
  • 500 mg for 7 days in divided doses
  • 100 mg for 1-3 months
  • Monitor for symptom resolution. People may have other conditions that may require higher dosages of vitamin C, or gut health support to optimize absorption.

For concerns with regard to oxalates/kidney stones:^6,11,12

• Dose greater than 500 mg/d can increase serum oxalate levels
  • Assess fat digestion and calcium intake to help reduce oxalate absorption

The possibility of oxalate nephropathy should not be ignored, but fear of it may increase disease burden for patients. Clinicians can help their patients focus on nourishing their body rather than fearing nutrients by staying current on guidelines and updates on vitamin C and CKD as well as referring to a trained renal dietitian to provide an individual needs assessment and dietary and supplement recommendations. So many of the nutrient recommendations associated with CKD focus on the harm of increased levels that the consequences of too little are overshadowed.  However, as individualized assessment and care becomes more widespread, clinicians will increase their clinical judgment and patients can reap a myriad of benefits from being well nourished.

Lindsey Zirker, MS, RD, is a renal dietitian who works with Kidney Nutrition Institute in Titusville, Florida. She specializes in autoimmune kidney disease and advanced practice medical nutrition therapy for patients with kidney disease.