Positive Health Online

Abstract

AUER and colleagues, Chemistry Department, University of Cape Town, South Africa studied the effect of ingestion of large doses of vitamin C upon urinary oxalate excretion and upon various biochemical and physicochemical risk factors associated with calcium oxalate stone formation. Additionally, urinary ascorbate excretion was determined and related qualitatively to ingested levels of vitamin C and oxalate excretion.

Background

Methodology

10 healthy men participated in the protocol in which 4 g vitamin C was ingested for 5 days . 24 hour urine samples were collected prior to, during and following the protocol. The urine collection procedure was designed to enable the analysis of oxalate in the presence and absence of an EDTA preservative and the analysis of vitamin C using manual titration. Physicochemical risk factors including calcium oxalate relative supersaturation and Tiselius risk index were calculated from urine composition.

Results

Erroneously high analytical oxalate levels occur in the absence 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, and levelled out after 24 hours, suggesting that metabolic pool saturation is reached within 24 hours, after which ingested ascorbic acid is excreted unmetabolised in the urine. Although transient statistically significant changes occurred in a certain of the biochemical risk factors, these were not regarded as being clinically significant. There were no changes in either the calcium oxalate relative supersaturation or Tiselius risk index.

Conclusion

Ingestion of large doses of vitamin C does not affect the principal risk factor associated with calcium oxalate kidney stone formation .

References

Aueer BL et al. The effect of ascorbic acid ingestion on the biochemical and physicochemical risk factors associated with calcium oxalate kidney stone formation. Clin Chem Lab Med 36(3): 143-7 Mar 1998.

Comment

Increased risk of kidney stone formation was one of the major "scare" stories used to discredit vitamin C supplementation over the past several decades. The origin of this and many other alleged dangers of vitamin C consumption was a hypothesis published, suggesting that perhaps vitamin C might increase the risk of kidney stone formation. There has never been demonstrated any such increased risk over many years and many such studies such as the one above investigating the evidence. It is, nevertheless, always a pleasure to see researchers conducting proper studies to establish the clinical evidence. Readers wishing to read about other "myths" of vitamin C consumption are referred to my book Goodman S. Vitamin C: The Master Nutrient (Keats, 1991).