Urinary and plasma oxalate during ingestion of pure ascorbic acid: a re-evaluation.

Daily ingestion of 8 g of pure ascorbic acid by 8 normal subjects for 7 days did not, in contrast to previous reports in the literature, significantly alter urinary or plasma oxalate during or after ingestion. When urine with raised ascorbate values was heated at 100 degrees C for 30 min, a significant increase in urinary oxalate concentration was observed. Plasma ascorbate reached a mean value during ingestion of 3.3 mg/100 ml. Urinary citrate excretion significantly decreased during the first 4 days of ascorbic acid ingestion; however, the urinary inhibitory activity of calcium oxalate crystal growth was not significantly altered. Urinary and serum urate as well as urinary calcium and magnesium were unaltered by ingestion of the vitamin supplement.