Inositol hexakisphosphate in urine: the relationship between oral intake and urinary excretion

Objective To study the relationship between the oral intake of inositol hexakisphosphate (InsP(6), phytic acid, an inhibitor of urinary crystallization) and Its urinary excretion, to establish their possible mutual influence. Materials and methods Two groups of male Wistar rats (six animals each) received either; tap water and normal rat food pellets (controls); or a liquid diet in which InsP(6) was absent and which then received gradually increasing amounts of InsP(6). The urinary levels of InsP(6) were then assessed regularly in both groups. Results When InsP(6) was absent from the diet, urinary excretion declined to undetectable levels after 22 days. The addition of increasing amounts of InsP(6) to the liquid diet caused an increase in its urinary excretion after about 10 days. Adding InsP(6) in amounts >425 mg/L caused no further increases in urinary excretion. Adding inositol (with no InsP(6)) to the liquid diet caused only a slight increase in the urinary excretion of InsP(6). Conclusion These results showed that InsP(6) urinary levels were related to its oral intake; consequently, a low consumption of InsP(6) would cause a urinary deficit of this crystallization inhibitor and thus an increase in the risk of developing urinary calcium stones. Although urinary excretion was dose-dependent, there was an ingested amount (20.9 mg/kg) above which there was no increase in the amount excreted. This intake is easily obtained by consuming a normal diet (rich in InsP(6)) indicating that to maintain appropriate urinary levels of InsP(6), the consumption of InsP(6) supplements is only necessary when the diet is particularly poor in InsP(6).