Hyperoxaluria in patients with idiopathic calcium nephrolithiasis.

We studied 476 patients with idiopathic renal calcium stone disease (286 M, 190 F) while they ate their customary diets. Each subject collected a 24-hour urine sample and completed a dietary diary for a 3-day period. Daily urinary oxalate excretion (M 0.24 +/- 0.15 mg/dl, F 0.23 +/- 0.15 mg/dl) and nutrient intake values were calculated and multiple regression analyses were performed. Daily urinary oxalate excretion was significantly (p < 0.001) related to urinary volume (R = 0.24), vitamin C intake (R = 0.33) and body mass index (R = 0.37) and inversely related to calcium intake (R = -0.35). We conclude that urinary oxalate reflects endogenous oxalate production, presumably related to body size, but also intestinal absorption of oxalate, related to dietary intake and to the effect of dietary calcium intake which reduces intestinal oxalate absorption.