STONE DISEASE

Quantitative assessment of citric acid in lemon juice, lime juice, and commercially-available fruit juice products
Penniston KL, Nakada SY, Holmes RP, Assimos DG
Department of Surgery, Division of Urology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, North Carolina
J Endourol. 2008; 22: 567-70

• Background and Purpose: Knowledge of the citric acid content of beverages may be useful in nutrition therapy for calcium urolithiasis, especially among patients with hypocitraturia. Citrate is a naturally-occurring inhibitor of urinary crystallization; achieving therapeutic urinary citrate concentration is one clinical target in the medical management of calcium urolithiasis. When provided as fluids, beverages containing citric acid add to the total volume of urine, reducing its saturation of calcium and other crystals, and may enhance urinary citrate excretion. Information on the citric acid content of fruit juices and commercially-available formulations is not widely known. We evaluated the citric acid concentration of various fruit juices.
• Materials and Methods: The citric acid content of 21 commercially-available juices and juice concentrates and the juice of three types of fruits was analyzed using ion chromatography.
• Results: Lemon juice and lime juice are rich sources of citric acid, containing 1.44 and 1.38 g/oz, respectively. Lemon and lime juice concentrates contain 1.10 and 1.06 g/oz, respectively. The citric acid content of commercially available lemonade and other juice products varies widely, ranging from 0.03 to 0.22 g/oz.
• Conclusions: 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. Ready-to-consume lemonade formulations and those requiring mixing with water contain </= 6 times the citric acid, on an ounce-for-ounce basis, of lemon and lime juice.
  
  
• Editorial Comment
  Citrate is the most abundant urinary organic ion and a potent inhibitor of crystallization, nucleation and crystal growth and aggregation. It acts by binding free calcium, binding to the calcium oxalate crystal surface, and blocking crystal-epithelial cell interactions. It may also impact urinary pH. This evaluation of the citric acid concentration of various fruit juices answers important questions that will help with the dietary counseling of our patients with stone disease.
  As with most good studies, it also provokes further questions worthy of investigation. How does the bioavailability of the dietary citrate sources differ, and how does each source impact urinary citrate and pH? Is there variability in citrate contents based on the climate or soil composition where the fruits were grown? Though citrate levels are lower for orange juice, potassium levels are higher - would the added alkali load with orange juice enhance urinary citrate excretion and offset its lower citrate level?
  For now, it is important we emphasize for patients that fresh or concentrated lemon or lime appears to be their best shot at squeezing their risk of stone recurrence.

Dr. Manoj Monga
Professor, Department of Urology
University of Minnesota
Edina, Minnesota, USA
E-mail: endourol@yahoo.com