THE EFFECT OF ASCORBIC-ACID INGESTION ON THE BIOCHEMICAL AND PHYSICOCHEMICAL RISK-FACTORS ASSOCIATED WITH CALCIUM-OXALATE KIDNEY-STONE FORMATION

The present study was undertaken to determine the effect of ingestion of large doses of vitamin C on urinary oxalate excretion and on a numb er of other biochemical and physicochemical risk factors associated wi th 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 partic ipated in a protocol in which 4 g ascorbic acid was ingested for 5 day s. Urines (24 h) were collected prior to, during and after the protoco l. The urine collection procedure was designed to allow for the analys is of oxalate in the presence and absence of an EDTA preservative and for the analysis of ascorbic acid by manual titration using 2,6 dichlo rophenolindophenol. Physicochemical risk factors such as the calcium o xalate relative supersaturation and Tiselius risk index were calculate d from urine composition. The results showed that erroneously high ana lytical oxalate levels occur in the asence of preservative. In the pre served samples there was no significant increase in oxalate excretion at any stage of the protocol. Ascorbate excretion increased when vitam in C ingestion commenced but levelled out after 24 hours suggesting th at saturation of the metabolic pool is reached within 24 hours after w hich ingested ascorbic acid is excreted unmetabolized in the urine. Wh ile transient statistically significant changes occurred in some of th e biochemical risk factors, they were not regarded as being clinically significant. There were no changes in either the calcium oxalate rela tive supersaturation or Tiselius risk index. It is concluded that inge stion of large doses of ascorbic acid does not affect the principal ri sk factors associated with calcium oxalate kidney stone formation.