The medical management of calcium urolithiasis depends on manipulating the balance of crystal promoters versus inhibitors. Nutrition therapy that is targeted to an individual patient’s risk factors is a basic strategy for kidney stone prevention and an appropriate adjunct to pharmacologic therapy. A cornerstone of prevention is achieving appropriate urine dilution by enhancing urine volume. This reduces the supersaturation of urine, a necessary first step in crystal formation.
A second goal in preventing calcium stone formation is to enhance the concentration of crystal inhibitors. Of these, citrate is the most clinically significant, as it may be manipulated by either diet or pharmacologic therapy or a combination thereof. While 320 mg (1.67 mmol) urinary citrate in a 24-hour urine collection is considered the cutoff for the definition of hypocitraturia,5
some clinicians target a 24-hour urinary citrate concentration of ≥600 mg (3.12 mmol), which is closer to the urinary citrate excretion of healthy, non–stone forming individuals.15
Hypocitraturia, if severe and/or persistent, usually requires pharmacologic therapy in the form of potassium citrate, which enhances urine pH and also citrate excretion. The identification and promotion of consumption of fluids that add to the crystal inhibitory potential of urine is appealing, not only to promote fluid intake but to enhance urinary citrate excretion. Citric acid is a naturally-occurring organic acid present in multiple fruits and their juices. Data on the citric acid content of fresh fruit juices and commercially-available fruit juice beverages may therefore prove useful in constructing nutrition therapy regimens for calcium stone formers.
Lemon and lime juice, both from the fresh fruit and from juice concentrates, provide more citric acid per liter than ready-to-consume grapefruit juice, ready-to-consume orange juice, and orange juice squeezed from the fruit. These data concur with those previously reported.2
As lemon and lime juice contain 38 and 35 mg potassium/oz, respectively, about the same as grapefruit juice and about 60% that of orange juice (potassium content obtained from the U.S. Department of Agriculture, Agricultural Research Service, USDA National Nutrient Database for Standard Reference, Release 19, Nutrient Data Laboratory Home Page: http://www.ars.usda.gov/main/site_main.htm?modecode=12354500
, accessed 07/02/2007), ingestion of lemon or lime juice on a daily basis could provide dietary alkali that would decrease renal tubular reabsorption of citrate, resulting in enhanced urinary citrate excretion. The distribution of lemon or lime juice in ample water or other fluid, consumed throughout the day, would also add to the volume of fluids ingested, resulting in enhanced urine output4
and reduced urine supersaturation.
Further research should determine the bioavailability of dietary citric acid from various sources and characterize the response to dietary citric acid in kidney stone formers who are hypocitraturic, as well as those who are normocitraturic. The impact of diet-derived citrate on urinary concentrations among calcium stone formers consuming different diets (e.g., high fruit/vegetable intake v
low fruit/vegetable intake; high meat intake v
low meat intake) should be assessed, as dietary patterns are known to influence urinary citrate concentrations.9