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Mode of action of cranberry in UTI

Recent research reveals that proanthocyanidins are key to the effectiveness of cranberry (Vaccinium macrocarpon Aiton, Ericaceae) in the treatment of urinary tract infections [Howell et al., 1998].

The laboratory study builds on earlier research which showed that cranberry works by preventing the adherence of bacteria to the walls of the urinary tract, not by acidifying the urine, as previously believed. Bacteria adhere to the walls of the urinary tract with specialized fibers called fimbriae, and may be classified according to the type of fimbriae by which they attach. The new study, reported in the New England Journal of Medicine, shows that proanthocyanidins are the compounds responsible for preventing the adherence of pathogenic "p-fimbriated" Escherichia coli to the lining of the urinary tract. According to the investigators, proanthocyanidins from other Vaccinium species, including blueberry (Vaccinium angustifolium Ait. and V. corybosum L., Ericaceae), show similar activity, while the condensed tannins of a wide range of other fruits and vegetables do not. Earlier research demonstrated that fructose in cranberry juice inhibits the attachment of "type 1 fimbriated" E. coli [Zafriri et al., 1989].

Clinical research has already documented the efficacy of cranberry juice in reducing bacteriuria (bacteria in the urine) and pyuria (pus in the urine). A double-blind, placebo-controlled study published in the Journal of the American Medical Association in 1994 showed that regular intake of cranberry juice "cocktail" significantly reduced the frequency of bacteriuria and pyuria in elderly women (see HerbalGram 32, page 15). The 153 women in the six-month study drank 300 ml daily of cranberry juice cocktail or a synthetic placebo drink with a similar flavor but no cranberry content [Avorn et al., 1994]. - Evelyn Leigh (HRF)

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[Avorn J, Monane M, Gurwitz JH, Glynn RJ, Choodnovskiy I, Lipsitz LA. Reduction of bacteriuria and pyuria after ingestion of cranberry juice. JAMA 1994;271(10): 751-754.

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Howell AB, Vorsa N, Der Marderosian A, Foo LY. Inhibition of the adherence of p-fimbriated Escherichia coli to uroepithelial-cell surfaces by proanthocyanidin extracts from cranberries. N Engl J Med 1998; 339(15): 1085-1086.

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Zafriri D, Ofek I, Adar R, Pocino M, Sharon N. Inhibitory activity of cranberry juice on adherence of type 1 and type P fimbriated Escherichia coli to eucaryotic cells. Antimicrobial Agents and Chemotherapy 1989; 33(1): 92-98.]

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