[Correlation between protein and sodium intake and calciuria in calcium lithiasis]

In order to assess the influence of dietary protein and salt intake on urinary calcium excretion in calcium stone formers, we simultaneously determined 24 hour urinary excretion of Urea (UU) and sodium (UNa) together with that of calcium (UCa) in 184 patients (112 males) with idiopathic calcium nephrolithiasis studied on free diet. Mean (+/- SEM) values expressed as mmol/kg BW/day of both UU and UNa were higher in hypercalciuric (UCa > or = 0.1 mmol/kg/d, mean 0.15 +/- 0.01) male patients, respectively 6.63 +/- 0.25 and 2.71 +/- 0.13, than in normocalciuric males, respectively 5.33 +/- 0.22 (p < 0.001) and 2.36 +/- 0.15 (p = 0.06), while the latter did not differ from healthy controls. Similar findings were made in female stone formers. Linear regression analysis on the whole series showed a positive but weak correlation between UU and UCa (r = 0.47, p < 0.001) and between UNa and UC a (r = 0.33, p < 0.001), but the slope of the relation UCa/UU was increased only in hypercalciurics, whereas it did not differ between normocalciurics and controls. By multiple regression analysis, variations of UU and UNa altogether accounted only for 22% of variation in UCa. We conclude that in both sexes hypercalciuric stone formers have a higher protein and sodium intake than normocalciurics, and for a given urinary urea output, their mean urinary calcium excretion is higher, thus suggesting that hypercalciuric stone formers are electively sensitive to the hypercalciuric effect of high protein intake.