Ascorbic Acid and Urinary Oxalate

Excerpt

To the editor: The report of Swartz and colleagues (1) deserves comment. The authors state, "Oral intake of large doses of ascorbic acid has been shown to increase oxalate excretion to levels of 60 to 622 mg/d, implying metabolic conversion of ingested ascorbic acid to oxalate ranging from 2.5% to 30% on a molar basis." They cite four studies as a source for these values. However, three of these studies used an inferior nonspecific method for measuring urinary oxalate. Only the study of Schmidt and coworkers (2) used the new, more specific isotachophoresis technique for oxalate analysis (SCHMIDT KH, HAGMAIER