title: Effects of an oxalate load on urinary oxalate excretion in calcium stone formers.
abstract: 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.
authors.affiliation: Nephrology Division, Universidade Federal de São Paulo, Brazil.
authors.forename: Claudia
authors.initials: C
authors.lastname: de O G Mendonça
authors.forename: Ligia Araújo
authors.initials: LA
authors.lastname: Martini
authors.forename: Alessandra Calábria
authors.initials: AC
authors.lastname: Baxmann
authors.forename: José Luiz
authors.initials: JL
authors.lastname: Nishiura
authors.forename: Lilian
authors.initials: L
authors.lastname: Cuppari
authors.forename: Dirce Maria
authors.initials: DM
authors.lastname: Sigulem
authors.forename: Ita Pfeferman
authors.initials: IP
authors.lastname: Heilberg
mesh_terms: 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*
chemical_list: D002136:Calcium, Dietary; D010070:Oxalates; D001205:Ascorbic Acid; D002118:Calcium