Effects of an oxalate load on urinary oxalate excretion in calcium stone formers.
OBJECTIVE
To investigate the oxalate intake and the effect of an oxalate load on urinary oxalate excretion in calcium stone-forming (CSF) patients.


METHODS
Prospective study.


METHODS
University-affiliated outpatient Renal Lithiasis Unit.


METHODS
Seventy (70) CSF and 41 healthy subjects (HS) collected a 24-hour urine sample and were submitted to a 3-day dietary record to determine mean oxalate (Ox), calcium (Ca) and vitamin C intake. Fifty-eight (58) CSF patients were randomly selected to receive milk (N = 28) or dark (N = 30) chocolate as an oxalate load.


METHODS
Administration of either milk (94 mg Ox + 430 mg Ca) or dark chocolate (94 mg Ox + 26 mg Ca) for 3 days. A 24-hour urine sample was obtained before and after the load to determine calcium, oxalate, sodium, potassium, urea, and creatinine.


METHODS
Oxalate intake and excretion.


RESULTS
CSF patients presented mean Ox intake of 98 +/- 137 mg/d, similar to that of HS (108 +/- 139 mg/d). Mean Ox and vitamin C intake was directly correlated with Ox excretion only in CSF. The consumption of dark chocolate induced a significant increase in mean urinary Ox (36 +/- 14 versus 30 +/- 10 mg/24 hr) not observed in the milk chocolate group. Thus, a 2-fold increase in Ox intake in this population of CSF patients produced a significant 20% increase in oxaluria, not observed when Ca was consumed simultaneously.


CONCLUSIONS
The present study suggests that even small increases in Ox intake affect oxalate excretion and the mitigation of urinary oxalate increase by Ca consumption reinforces that Ca and Ox intakes for CSF patients should be in balance. Further studies are necessary to assess whether or not a 20% increase in oxaluria will lead to a higher risk of stone formation.
de O G Mendonça
Claudia
C
Nephrology Division, Universidade Federal de São Paulo, Brazil.
Martini
Ligia Araújo
LA
Baxmann
Alessandra Calábria
AC
Nishiura
José Luiz
JL
Cuppari
Lilian
L
Sigulem
Dirce Maria
DM
Heilberg
Ita Pfeferman
IP
D000328:Adult; D000818:Animals; D001205:Ascorbic Acid / Q000008:administration & dosage; D002099:Cacao / Q000737:chemistry; D002118:Calcium / Q000494:pharmacology*; D002136:Calcium, Dietary / Q000008:administration & dosage; D015930:Diet Records; D005260:Female; D006801:Humans; D006959:Hyperoxaluria / Q000453:epidemiology* / Q000209:etiology; D007669:Kidney Calculi / Q000209:etiology* / Q000517:prevention & control; D008297:Male; D008892:Milk / Q000737:chemistry; D010070:Oxalates / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000652:urine*
D002136:Calcium, Dietary; D010070:Oxalates; D001205:Ascorbic Acid; D002118:Calcium