Effect of ascorbic acid consumption on urinary stone risk factors.
OBJECTIVE
Ascorbic acid (AA) has been implicated as a risk factor for calcium oxalate stones due to its conversion to oxalate and potential acidifying properties. We evaluated the effect of AA consumption on urinary saturation of calcium oxalate (CaOx) and urinary pH.


METHODS
A total of 12 normal subjects (NS) and 12 CaOx stone formers (SF) underwent 2, 6-day phases of study while maintained on a controlled metabolic diet. In each phase subjects ingested 1 gm AA or an identical appearing placebo twice daily. On the last 2 days of each phase 2, 24-hour urine collections were analyzed for pH and stone risk factors, and blood specimens were submitted for serum chemistry studies.


RESULTS
No difference in urinary pH was found between placebo and AA phases in NS (6.02 versus 6.02) and SF (6.0 versus 6.0). However, urinary oxalate was statistically significantly higher in the AA versus placebo phase for NS (34.7 versus 28.5 mg, p = 0.008) and SF (41.0 versus 30.5 mg, p <0.001). Likewise, the CaOx relative saturation ratio was significantly higher in the AA versus placebo phase for both groups.


CONCLUSIONS
Ingestion of 2 gm AA daily results in no change in urinary pH but a moderate though statistically significant increase in urinary oxalate in NS (20%) and SF (33%). Stone formers respond no differently to AA than normal subjects. We recommend limiting AA use to less than 2 gm daily in CaOx stone formers.
Traxer
Olivier
O
Department of Urology, The University of Texas Southwestern Medical Center, Dallas, 75390-9110, USA.
Huet
Beverley
B
Poindexter
John
J
Pak
Charles Y C
CY
Pearle
Margaret S
MS
D000328:Adult; D001205:Ascorbic Acid / Q000009:adverse effects*; D002129:Calcium Oxalate / Q000652:urine; D018592:Cross-Over Studies; D019587:Dietary Supplements / Q000009:adverse effects*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D012307:Risk Factors; D014545:Urinary Calculi / Q000139:chemically induced* / Q000652:urine
D002129:Calcium Oxalate; D001205:Ascorbic Acid