Effect of High and Low Calcium Diets on Stone Forming Risk During Liberal Oxalate Intake
Received 20 May 2005
Purpose
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.
Materials and 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.
aDepartment of Urology, The University of Texas Southwestern Medical Center, Dallas, Texas
bCenter for Mineral Metabolism and Clinical Research, The University of Texas Southwestern Medical Center, Dallas, Texas
cCenter for Biostatistics and Clinical Science, The University of Texas Southwestern Medical Center, Dallas, Texas
Correspondence: Department of Urology, UT Southwestern Medical Center, 5323 Harry Hines Blvd., J8.106, Dallas, Texas 75390-9110 (telephone: 214-648-6853; FAX: 214-648-8786).
Study received Institutional Review Board approval.
Supported by United States Public Health Service Grants M01-RR00633 and P01-DK20543 from the National Institutes of Health.
Editor’s Note: This article is the fourth of 5 published in this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the questions on pages 418 and 419.
ABSTRACT