Nephrology Dialysis Transplantation, Vol 13, Issue 9 2241-2247, Copyright © 1998 by Oxford University Press
B Hess, C Jost, L Zipperle, R Takkinen and P Jaeger
Background: The aim of the study was to test whether
increasing dietary calcium intake lowers intestinal oxalate absorption and
thereby prevents hyperoxaluria and urinary crystallization during a 20-fold
normal oxalate load in healthy subjects. Methods:
Fourteen healthy male volunteers (age 23-44 years, BMI 21.5-27.7
kg/m2) collected 24-h urines while on free choice
diet as well as on two standardized diets. The latter contained 2545 kcal,
2500 ml of mineral water, 102 g of protein, 13.6 g of sodium chloride and
2220 mg of oxalate ( 20-fold content of an average diet). Subjects were
studied twice while on the standardized diet, once while eating a normal
amount of calcium (1211 mg/day, oxalate-rich, diet), and once while eating
3858 mg of calcium /day (calcium and oxalate-rich diet).
Results: Compared with the free-choice diet
(322±36 &mgr;mol/d), UOx X V increased to 780±722
&mgr;mol/d on the oxalate-rich diet (P=0.001) and fell again to
326±31 &mgr;mol/d on calcium and oxalate-rich diet (P=0.001
vs oxalate-rich diet). Urinary glycolate (a metabolic
precursor of Ox) always remained below the upper limit of the normal range
and did not change between different diets, indicating that changes in UOx
x V reflect respective variations in intestinal absorption of Ox. UCa x V
was 4.60±0.45 mmol/d on the free choice diet and
3.20±0.32 mmol/d on the oxalate-rich diet (P=0.011
vs free-choice diet); it increased to
7.28±0.74 mmol/d on the calcium- and oxalate-rich diet (P=0.001
vs free-choice and oxalate-rich diets). As indicated
by the AP (CaOx) index (Tiselius), urinary supersaturation did not vary
significantly between the three diets. In freshly voided morning urines
(studied in 8/14 subjects) on the oxalate-rich diet, CaOx crystals or
crystal aggregates of up to 80 &mgr;m diameter were found in 5/8
urines, whereas this never occurred on the free-choice diet and only once
on the calcium- and oxalate-rich diet. Conclusion:
Increasing calcium intake while eating Ox-rich food prevents dietary
hyperoxaluria and reduces CaOx crystallization in healthy subjects. This
further illustrates that dietary counseling to idiopathic calcium-stone
formers should ensure sufficient calcium intake, especially during
oxalate-rich meals. Key words: calcium oxalate
crystallization; dietary calcium; hyeprcalciuria; hyperoxaluria; oxalate
load; urinary supersaturation
ORIGINAL ARTICLES
High-calcium intake abolishes hyperoxaluria and reduces urinary crystallization during a 20-fold normal oxalate load in humans
Department of Medicine and Policlinic of Medicine, University Hospital, CH-3010 Berne, Switzerland; Corresponding author
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