Cranberry Juice and Urinary Stones
Cranberry Juice and Urinary Stones
By Gerald T. Keegan, MD, FACS Emeritus Staff, Scott & White Clinic and Hospital Former Professor of Surgery (Urology), Texas A&M University School of Medicine, Temple, TX. Dr. Keegan reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
Source: Gettman MT, et al. Effect of cranberry juice consumption on urinary stone risk factors. J Urol 2005;174:590-594.
Abstract: The authors evaluated the effect of cranberry juice on urinary stone risk factors. A total of 12 normal subjects and 12 calcium oxalate stone formers underwent two 7-day phases of study in random order while on a controlled metabolic diet. Subjects ingested 1 L of cranberry juice daily in one phase and 1 L of deionized water in the other phase. On the last two days of each phase, two 24-hour urine collections and blood samples were obtained for stone risk factors and serum chemistries. No significant differences were found between normal subjects and stone formers in response to cranberry juice and, therefore, the groups were combined. Cranberry juice significantly increased urinary calcium (from 154 mg/d to 177 mg/d, P = 0.0008) and urinary oxalate (from 26.4 mg/d to 29.2 mg/d, P = 0.04), thereby increasing urinary saturation of calcium oxalate by 18%. Urinary citrate was unchanged and urinary magnesium increased slightly. Urinary pH decreased (from 5.97 to 5.67, P = 0.0005), and urinary ammonium, titratable acidity, and net acid excretion increased during cranberry juice ingestion. Urinary uric acid decreased (from 544 mg/d to 442 mg/d, P < 0.0001) as did serum uric acid. Thus, the urinary saturation of brushite and monosodium urate was reduced by cranberry juice but the amount of undissociated uric acid increased. The authors concluded that cranberry juice exerts a mixed effect on urinary stone forming propensity. It reduces urinary pH likely by providing an acid load and decreases urinary uric acid perhaps by retarding urate synthesis. Overall, cranberry juice increases the risk of calcium oxalate and uric acid stone formation but decreases the risk of brushite stones.
This article in the August 2005 Journal of Urology discusses the effect of cranberry juice consumption on urinary stone risk factors. Although cranberry juice has been found to be of some effect both in the prevention and treatment of urinary tract disorders,1 most urologists do not recommend it in stone formers due to its acidifying effects and oxalate content.
The underlying reasons for stone formation in the urinary tract involve complex metabolic mechanisms. Urinary stones do not form unless crystals of the offending substance form in the urine. For crystallization to occur, the urine generally needs to be supersaturated with the particular combination of agents technically termed as salts (as in the product of an acid and a base). The acidity/alkalinity of the urine potentiates or reduces the supersaturation of the individual salts. For example, uric acid is very soluble in an alkaline urine with a pH of 7.5, whereas it crystallizes in a urine with a pH of 5. However, urinary supersaturation by itself does not explain stone formation. Non-stone formers have substances in their urine that inhibit crystal formation growth and aggregation. One of the most studied of these inhibitors is that group of substances known as citrates, which can be obtained from natural sources including many citrus fruits. People who form stones chronically frequently are deficient in these substances. Determination of the stone composition also is helpful in elucidating the underlying causes of stone disease.
The most common type of urinary tract stone is one made of calcium oxalate. There are two forms of this compound: weddellite (calcium oxalate dehydrate) and whewellite (calcium oxalate monohydrate). Although most calcium oxalate stones are idiopathic, there are both hereditary and dietary forms of this type of hyperoxaluria, the most predominant of which is the dietary. I advise people who form this type of stone, especially those with elevated urinary oxalate levels, to avoid excess consumption of oxalate-containing substances in fruits (such as cranberries, plums, and rhubarb) and vegetables (such as arugula, Swiss chard, and spinach). Excess consumption of vitamin C and chocolate also should be avoided.
Another rarer type of urinary stone is the uric acid stone, which forms predominantly in acid urine. Acidic urine is an underlying characteristic of this type of stone former. The treatment of these patients involves alkalinization of the urine as well as hydration. Cranberry juice is an acidifier and hence serves only to exacerbate the acidity in which uric acid stones crystallize. In addition, the uric acid crystals forming in an acid urine may serve as a nidus (like the string that is used to make rock candy) upon which the calcium oxalate stones crystallize, which further complicates the use of cranberry juice in these patients.
In the Gettman study, cranberry juice reduced the urinary saturation of brushite (calcium hydrogen phosphate dehydrate).2 Brushite stones as solitary stones are exceedingly rare and occasionally point to serious underlying metabolic derangements. I would not recommend cranberry juice for preventing this type of stone despite the findings of decreased saturation. Although the series of 24 patients is small, the results clearly demonstrate that cranberry juice produces a significant increase in urinary calcium (not good for stone formers) as well as an increase in the urinary oxalate levels. When oxalates are combined with calcium in the urine beyond their solubility point they tend to crystallize from the urine and produce stones. The urinary pH (a measure of acidity/alkalinity) decreased toward the acid side, and although the saturation of monosodium urates was reduced, the amount of undissociated uric acid available for crystallization increased.
Although not specifically mentioned in the Gettman study, one stone type that always needs to be excluded is the struvite stone (magnesium ammonium phosphate) that occurs in the presence of an alkaline urine and is caused by urea splitting organisms, which break down urea in the urine to produce ammonia. The stones formed become a nidus for additional stone formation and aggregation. It is conceivable that people who form this type stone, after having their infections eradicated and their stones completely resolved, might benefit from the bacterial suppressive effects of cranberry juice. However, in the presence of more effective therapy, I would be reluctant to recommend this course of action.
The best advice for people who are chronic stone formers is to have a metabolic workup including blood studies and a 24-hour urine test to exclude serious underlying disease. If no major abnormalities are detected, the best way to prevent new stones is to consume large quantities of fluids (64 ounces of water a day for hydration and with lemon juice added to the water to provide citrates that may retard stone crystallization). Most people also benefit from reducing salt and protein in their diets. Both of these substances will produce excess levels of calcium in the urine. Contrary to popular belief, the restriction of calcium in the diet is not beneficial for most stone formers and is generally detrimental.3-5
1. Keegan L. Cranberries and urinary tract infections. Altern Ther Women's Health 2003;5:25-29.
2. Gettman MT, et al. Effect of cranberry juice consumption on urinary stone risk factors. J Urol 2005;174:590-594.
3. Stitchantrakul W, et al. Effects of calcium supplements on the risk of renal stone formation in a population with low oxalate intake. Southeast Asian J Trop Med Public Health 2004;35:1028-1033.
4. Straub M, Hautmann RE. Developments in stone prevention. Curr Opin Urol 2005;15:119-126.
5. Curhan GC, et al. Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II. Arch Intern Med 2004;164:885-891.Keegan GT. Cranberry juice and urinary stones. Altern Ther Women's Health 2005;9(10):77-78.
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