Effect of grapefruit juice on urinary lithogenicity

Purpose: An increased risk of nephrolithiasis has been associated with the ingestion of grapefruit juice in epidemiological studies. To our knowledge the basis of this effect of grapefruit juice has not been studied previousl y. We studied the effect of grapefruit juice consumption on urinary chemist ry and measures of lithogenicity. Materials and Methods: Ten healthy men and women between ages of 25 and 40 years participated. Each subject drank 240 mi. of tap water at least 3 time s daily for 7 days during the control period. This period was followed by a second 7 days experimental period during which they drank 240 ml. of grape fruit juice 3 times daily. In each 7-day period urine was collected for 24 hours during the last 3 days. Urine chemical analysis was performed, supers aturations of calcium oxalate, calcium phosphate and uric acid were calcula ted and urinary lithogenicity was measured. Results: Urine volume and creatinine excretion were the same during the con trol and experimental periods. Grapefruit juice ingestion was associated wi th an increase in mean oxalate excretion plus or minus standard deviation o f 41.1 +/- 9.2 to 51.9 +/- 12.0 mg. per 24 hours (p = 0.001) and in mean ci trate excretion of 504.8 +/- 226.5 to 591.4 +/- 220.0 mg. per 24 hours (p = 0.01). There was no net change in the supersaturation or upper limit of me tastability of calcium oxalate, calcium phosphate or uric acid. Crystal agg regation and growth inhibition by urinary macromolecules was not affected b y grapefruit juice ingestion. Conclusions: Offsetting changes in urine chemistry caused by the ingestion of grapefruit juice led to no net change in calculated supersaturation. No changes in lithogenicity were demonstrated. The results do not demonstrate an effect of grapefruit juice for increasing lithogenicity. The basis of th e observations of epidemiological studies remain unexplained.