Effect of high and low calcium diets on stone forming risk during liberal oxalate intake.
OBJECTIVE
Recent studies suggest that a high calcium diet protects against calcium oxalate stone formation. We compared the effect of high and low calcium diets on urinary saturation of calcium oxalate during liberal oxalate intake.


METHODS
A total of 10 healthy subjects (5 male, 5 female) participated in a 2-phase, randomized, crossover study comparing high (1,000 mg daily) and low (400 mg daily) calcium intake on a liberal oxalate diet (200 mg daily). During each phase subjects adhered to an instructed diet for 3 days followed by a controlled, metabolic diet for 4 days. Blood and 24-hour urine specimens collected on the last 2 days of each phase were analyzed for serum biochemistry studies and stone risk factors, respectively.


RESULTS
Urinary calcium was higher (mean +/- SD 171 +/- 64 vs 124 +/- 49 mg daily, p = 0.002) and oxalate was lower (25 +/- 4.8 vs 27 +/- 4 mg daily, p = 0.02) on the high vs low calcium diet. Overall, the urinary relative saturation ratio of calcium oxalate was higher on the high compared with the low calcium diet (3.3 vs 2.5, p <0.0001) even after adjusting for confounding variables.


CONCLUSIONS
In normal subjects urinary saturation of calcium oxalate was higher on a high calcium diet than a low calcium diet during liberal oxalate intake because the decrease in urinary oxalate did not overcome the effect of increased calcium. A high calcium diet during liberal oxalate intake may pose an increased risk of calcium oxalate stone formation.
Matsumoto
Edward D
ED
Department of Urology, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
Heller
Howard J
HJ
Adams-Huet
Beverley
B
Brinkley
Linda J
LJ
Pak
Charles Y C
CY
Pearle
Margaret S
MS
D000328:Adult; D002118:Calcium / Q000652:urine; D002129:Calcium Oxalate / Q000652:urine*; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000009:adverse effects; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D010070:Oxalates / Q000008:administration & dosage*; D012307:Risk Factors; D014545:Urinary Calculi / Q000209:etiology / Q000517:prevention & control* / Q000652:urine
D002136:Calcium, Dietary; D010070:Oxalates; D002129:Calcium Oxalate; D002118:Calcium