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The daily ingestion of cranberry products—juice or capsules—has been promoted as a means to prevent recurrent urinary tract infection (UTI) since at least the first half of the last century.1 In that preantibiotic era, acidification of the urine was a recommended treatment for UTI. Initially, cranberry juice was explored as an approach to treating UTI following the observation that it could lower urine pH. This is attributed to formation of hippuric acid through metabolism of the quinic acid present in cranberry juice. Later studies reported that the concentration of hippuric acid in the urine was insufficient for an antibacterial effect unless very large volumes of cranberry juice were ingested. Subsequently, some lectins (proanthocyanidins) present in cranberries as well as blueberries were reported to inhibit binding of the type 1 P-fimbriae of Escherichia coli to uroepithelial cells, preventing bacterial adherence within the urinary tract. This proposed mechanism for a beneficial effect of cranberries has not yet been shown to have a role in human infection.2 Even though many clinical trials evaluating the use of cranberry products for prevention of UTI have been reported, results have been inconsistent and the efficacy, if any, remains unknown after almost 100 years.
Nicolle LE. Cranberry for Prevention of Urinary Tract Infection? Time to Move On. JAMA. 2016;316(18):1873–1874. doi:10.1001/jama.2016.16140
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