If there's one beverage that holds the distinction of delivering prophylactic or therapeutic results, it's cranberry juice. A subject of urban mythology, cranberry juice is touted as being capable of both preventing and treating urinary tract infection (UTI). Indeed, in one study researchers compared 100 college-aged women with recurrent UTI (drinking one or more glasses of cranberry juice daily) to 113 controls.1
Urinary tract infection is defined by a specific threshold count of bacteria in the urine, which can manifest throughout the length of the urinary tract, attended by the presence of white blood cells in the urine and certain symptoms, such as urination-associated pain, urgency and frequency. Cranberries (Vaccinium macrocarpon) are unique to North America and are a rich source of proanthocyanidins (PCs). These PCs are hailed as the primary urinary tract-bioactive fraction of cranberries, due to their ability to inhibit the attachment and adherence of suspected UTI culprit bacteria, especially to the cells lining the urinary tract.2,3,4,5
Numerous researchers have undertaken clinical studies of varying rigor and design to further investigate cranberry juice and solid dosage forms (tablets or capsules). However, researchers have not tested cranberry juice cocktail with added sweetener and vitamin C, the most commonly consumed form of cranberries. In a systematic review of clinical trials assessing the efficacy of cranberry products in UTI, investigators found no randomised trials showing a therapeutic effect.6
Two more recent randomised trials with cranberry products provide evidence of efficacy, and also suggest that another type of adherence, specifically the supplementation regimen, may prove challenging. In one study, 50 women with prior UTI who took one tablet of concentrated cranberry juice (30 times concentration) twice daily, or another 50 that drank 250ml of unsweetened cranberry concentrate three times a day for a year (n=50), reduced their incidence of symptomatic UTI.7 The women who took tablets had a 14 per cent lower risk of symptomatic UTI compared with placebo, whilst those drinking the concentrate experienced a 12 per cent risk reduction. However, compliance with the unsweetened cranberry juice concentrate was less than with those taking tablets, a finding that resulted from a pediatric study.8 From an economic vantage, the annual cost of maintaining such a daily regimen is not insignificant: approximately $1,400 for cranberry juice concentrate and $624 for tablets.7
In relation to a different kidney condition, some evidence suggests that cranberry products may modify the development of kidney stones in susceptible individuals. Cranberry juice harbors a notable amount of oxalate9 and, when combined with calcium, can produce the most common form of kidney stone. In one study, researchers found administration of a cranberry juice tablet to five normal subjects produced a marked increase in urinary oxalate, but they also reported an increase in urinary potassium and magnesium, which are kidney stone inhibitors. However, in a different study in which researchers used a sweetened cranberry juice, they noted the same results, as well as acidification of the urine. This suggests cranberry juice may help reduce the risk of developing certain types of kidney stones.11 Clearly more research is needed to transform the legend of cranberry juice into compelling evidence-based practice.
Anthony Almada, BSc, MSc, is the president and chief scientific officer of IMAGINutrition Inc and has been a co-investigator on more than 60 randomised controlled trials. www.imaginutrition.com
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2. Ofek I, et al. Anti-Escherichia coli adhesion activity of cranberry and blueberry juices. New Engl J Med 1991;324:1599 (letter).
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