The Effect of Ascorbic Acid Ingestion on the Biochemical and Physicochemical Risk Factors Associated with Calcium Oxalate Kidney Stone Formation

Abstract

The present study was undertaken to determine the effect of ingestion of large doses of vitamin C on urinary oxalate excretion and on a number of other biochemical and physicochemical risk factors associated with calcium oxalate urolithiasis. A further objective was to determine urinary ascorbate excretion and to relate it qualitatively to ingested levels of the vitamin and oxalate excretion. Ten healthy males participated in a protocol in which 4 g ascorbic acid was ingested for 5 days. Urines (24 h) were collected prior to, during and after the protocol. The urine collection procedure was designed to allow for the analysis of oxalate in the presence and absence of an EDTA preservative and for the analysis of ascorbic acid by manual titration using 2,6 dichlorophenolindophenol. Physicochemical risk factors such as the calcium oxalate relative supersaturation and Tiselius risk index were calculated from urine composition. The results showed that erroneously high analytical oxalate levels occur in the asence of preservative. In the preserved samples there was no significant increase in oxalate excretion at any stage of the protocol. Ascorbate excretion increased when vitamin C ingestion commenced but levelled out after 24 hours suggesting that saturation of the metabolic pool is reached within 24 hours after which ingested ascorbic acid is excreted unmetabolized in the urine. While transient statistically significant changes occurred in some of the biochemical risk factors, they were not regarded as being clinically significant. There were no changes in either the calcium oxalate relative supersaturation or Tiselius risk index. It is concluded that ingestion of large doses of ascorbic acid does not affect the principal risk factors associated with calcium oxalate kidney stone formation.

Preliminary Clinical Study of the Effect of Ascorbic Acid on Colistin-Associated Nephrotoxicity

“…Ascorbic acid at 4 g/day was chosen for this study because such a dosage was reported to be safe without increased urinary oxalate (44,45) and a similar dose was found to be effective in a previous clinical study for preventing nephrotoxicity after contrast medium injection (46). In this study, the overall incidence of nephrotoxicity, determined according to the widely used RIFLE criteria (39), was 50 to 60%, and it was not significantly different from that observed in the patients at Siriraj Hospital in 2007 (47).…”

Criteria and Recommendations for Vitamin C Intake

“…49,50 Despite better assays, controversy remains. 33,[51][52][53][54][55][56] Taken together, the data show that oxalate excretion is probably increased at vitamin C doses of 1 g or more daily in some healthy people, although consequences are unclear. In people with underlying hyperoxaluria, oxalate excretion is accelerated by ascorbate doses of 1 g or more, and for these people megadoses could be harmful.…”

Guidelines on Urolithiasis<footref rid="foot01">¹</footref>

“…Vitamin C in doses up to 4 g per day can be taken without increasing the risk of stone formation [48]. Animal protein should not be ingested in excessive amounts [49, 50].…”