Epidemiologic evidence for the role of oxalate in idiopathic nephrolithiasis.

The importance of dietary and urinary oxalate in the formation of calcium oxalate kidney stones is widely accepted. Although the epidemiologic evidence for the role of oxalate remains largely indirect, recent prospective observations suggest its importance. The inverse association between dietary calcium intake and the risk of stone formation may be attributable to decreased gastrointestinal absorption of dietary oxalate and, thus, lower urinary oxalate concentrations. Further, the decreased risk of stone formation in women who consume large doses of vitamin B6 may be secondary to decreased oxalate production. The increased risk of nephrolithiasis observed with increasing body size may also be secondary to increased endogenous oxalate production. However, the frequency of hyperoxaluria is not substantially different in cases and controls for either sex. Notably, men have both higher stone incidence rates and higher mean urinary oxalate concentrations than women. Additional studies are needed to determine more precisely the role of dietary oxalate. More valid and comprehensive information on the oxalate content of food are desperately needed. Because the data on dietary oxalate are inconclusive, the routine restriction of dietary oxalate needs to be reexamined.