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)
[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.
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.
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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