CHICAGO—New study findings presented at the 2016 Kidney Week meeting may help researchers arrive at the optimal dose of vitamin C (ascorbic acid) supplementation for improving anemia in hemodialysis (HD) patients.

The current findings suggest that HD patients should not take more than 120 mg per day.  

William D. Sirover, MD, of Cooper Medical School of Rowan University in Camden, New Jersey, represented the research group that originally consisted of himself and Garry Handelman, PhD, of University of Massachusetts in Lowell.

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“The problem is that vitamin C gets metabolized to oxalate and escalating dosages of vitamin C could increase plasma oxalate levels.  If plasma oxalate levels surpass 30 uM, that could be a concern for oxalate precipitating in tissues and causing pathologic effects,” Dr. Sirover said. “Available literature indicates that a achieving a plasma vitamin C level of 70 uM may be the most effective and safe range for reducing erythropoiesis-stimulating agent (ESA) dose, as plasma vitamin C levels of 70–100 uM are not associated with plasma oxalate levels exceeding 30 uM.”     

At this time, the clinical issue is to identify an ascorbic acid dose that maintains plasma vitamin C between 70-100 uM, without plasma oxalate surpassing 30 uM.

In a study of 197 HD patients, Dr Sirover and colleagues examined the safety and efficacy of escalating doses of ascorbic acid supplementation: 50–75, 100–120, and 150 mg or more per day. These doses resulted in mean pre-HD plasma levels of 38.9, 48.9, and 258.1 uM, respectively. The corresponding pre-HD plasma oxalate levels were 17.3, 22.5, and 40.5 uM, respectively.

“Plasma oxalate levels were above 30 uM in patients who took 150 mg or more of ascorbic acid per day, so our data tell us that ascorbic acid supplementation to this degree may be too much for patients.”  Based on their findings, the team concluded that, for now, HD patients should avoid an ascorbic acid dose exceeding 120 mg per day. 

Also, “ our present understanding is that moderate ascorbic acid supplementation, which we defined as up to 120 mg per day, is not associated with concerning increases in plasma oxalate,” Dr. Sirover told Renal & Urology News. However, patients who received moderate ascorbic acid supplementation had plasma ascorbic acid levels lower than 70 uM, which may be insufficient for lowering ESA resistance.

“An important clinical objective is to find out what dose of ascorbic acid will achieve a plasma vitamin C level of 70 to 100 uM without surpassing concerning levels of plasma oxalate,” Dr. Sirover said.

Click here for more coverage from the American Society of Nephrology’s Kidney Week 2016 in Chicago.


  1. Sirover WD, Liu Y, Logan A, et al. Association of ascorbic acid supplementation with plasma ascorbic acid and oxalate levels in prevalent hemodialysis patients. Poster presented at the 2016 Kidney Week meeting in Chicago, Nov. 15-20. Poster TH-PO734.