Urinary tract infections are caused by bacterial overgrowth, are most prevalent in women, and are most commonly treated with antibiotics. However with increasing use of antibiotics comes the problem of antibiotic resistance and associated infections. Therefore there is interest in novel ways to treat urinary tract infections that does not rely on the use of antibiotics. One such method that has been investigated is the use of cranberry juice. A number of studies have investigated the use of cranberry juice on urinary tract infections and generally its use has been seen to be effective. For example, in one study, researchers investigated the effects of cranberry juice on women with a history of urinary tract infections. The women consumed the cranberry juice (240 mL per day) or instead consumed a placebo drink containing no cranberry juice, for 24 weeks. The results showed that here were only 39 diagnosed cases of urinary tract infections in the cranberry juice compared to 67 episodes in the placebo group.
Cranberries may have particularly useful properties that protect consumers from urinary tract infections. One mechanism that has been proposed for the beneficial effects of cranberries on urinary tract infections is the ability of polyphenols within the berries to adhere to proteins on bacteria. One group of polyphenols, the flavonoids may be particularly beneficial in this regard. Proanthocyanidins are a sub-group of polyphenols that have shown the ability to prevent adherence of bacteria. Other berries also contain these proanthocyanidins and may be useful in this regard also. However, cranberry appears to be the best berry for preventing this adherence in the urinary tract. Elderberry polyphenols for example, may have the ability to bind to pathogens and in this way limit infections of upper respiratory tract infections. This is another reason that berries should be a regular part of a healthy diet where possible.
Therefore the use of cranberry juice is evidenced to be beneficial against the development of urinary tract infections in those with a history of infections. It is not fully understood why cranberry juice is so effective against urinary tract infections. However mechanistic studies suggest that components of cranberry interfere with the attachment of E. coli to the epithelial cells of the urinary tract. In addition, the cranberry juice may provide an anti-inflammatory effect on the epithelial lining of the urinary tract. This latter effects may explain why in those cases where infection still occurs, symptoms are not present along with the infection. One possible component in cranberries that shows the ability to prevent the adhesion of bacteria to human cells are proanthocyanidins. These compounds are responsible for the bitter taste of cranberries and contribute to the red colour to the berries. The process may involve the binding of proanthocyanidins to proteins on E. coli, which in turn inhibits their attachment to host cells.
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