Cranberry: Folk wisdom prevails for prevention of urinary tract infections

According to folk wisdom, "cranberry juice can be used to prevent the occurrence of urinary tract infections (UTI)," shares James C. Fleet, Ph.D., from the Human Nutrition Research Center on Aging at Tufts University, Boston, in a review of the scientific evidence in favor of cranberry juice. UTIs cause frequent, painful urination; and the condition is far more common in women than in men.

Cranberry's mechanism of action debated
Although modern science has not necessarily doubted the health benefits of cranberries, there has been debate about how cranberries prevent UTIs.

Early researchers at the turn of this century suggested that cranberries -- a very tart fruit -- acidified the urine and in this way made the bladder inhospitable to the bacteria that cause UTIs. As an extension of this work, scientists in the 1920s demonstrated that cranberries did, in fact, increase the urinary excretion of hippuric acid, an organic acid which acidifies urine. However, contemporary research suggests that cranberry may do what it does by mechanisms other than lowering the pH of urine.

More recent scientific work has focused on the ability of cranberries to prevent the adherence of bacteria to the urinary tract lining. Bacteria that attach to the mucus lining of the urinary tract are more likely to contribute to an infection, while unattached bacteria are harmlessly eliminated when the bladder is emptied. Laboratory research demonstrates that cranberry juice contains at least two separate compounds which interfere with the ability of E. coli (the bacteria most frequently associated with urinary tract infections) to stick to the urinary tract lining. Blueberries, a closely related berry to cranberries, also contain the compounds that prevent the bacterial attachment of E. coli in the bladder.

Tracking the effect of cranberry in people
Going beyond laboratory work, studies in actual people confirm that cranberry juice does have an anti-UTI action. One clinical trial, one which studied elderly women prone to developing bladder infections, found that cranberry juice reduced the incidence of urinary tract infections. When the 153 elderly women drank either 12 ounces of cranberry juice every day for six months or a similarly tasting but inactive beverage, the women drinking the cranberry juice were only half as less likely to develop bladder infections. However, it may take four to eight weeks of daily use before cranberry juice affects the risk of bacterial infection.

Children with medical conditions requiring self-catheterization, which can increase the risk for urinary tract infections, may also benefit from cranberry juice. A small study, of 16 such children with spina bifida, tracked the presence of white and red blood cells in their urine (markers of infection) while the children drank two to three glasses of cranberry juice daily. At the beginning of the study, most of the children had measurable levels of red and white blood cells in their urine, these levels dropped after they drank the cranberry juice for two weeks.

Cases of chronic kidney infection, kidney inflammation, and painful urination may also benefit from cranberry. In addition, cranberry juice may improve the skin problems frequently affecting people with urostomies (an opening in the abdomen made to allow for the drainage of urine into a bag). A study of 13 individuals with urostomies, in which six of the 13 patients exhibited skin problems at the beginning of the study, found that drinking cranberry juice daily for six months improved the skin conditions in five of these six patients.

Because cranberries are naturally tart, many cranberry juices are sweetened to make them more palatable, which also brings undesirable sugar and extra calories to the diet. Drinks called "cranberry cocktail" generally have only a small amount of cranberry juice and far more sweeteners; cranberry juice is a better choice. Supplements of cranberry extract are also a great alternative to drinking large amounts of the tart juice.

Avorn, J., Monane, M., Gurwitz, J.H., et at "Reduction of bacteriuria and pyuria after ingestion of cranberry juice," JAMA 271(10):751-754, 1994.

Fleet, J.C. "New support for a folk remedy: Cranberry juice reduces bacteriuria and pyuria in elderly women," Nutr Rev 52:168-178, 1994.

Rogers, J. "Pass the cranberry juice," Nursing Times 87(48):36-37, 1991.

Tsukada, K., Tokunaga, K., Iwama, T., et al. "Cranberry juice and its impact on peri-stomal skin conditions for urostomy patients," Ostomy/Wound Management 40(9):60-67, 1994.


By Victoria Dolby, M.P.H.

Adapted by M.P.H.

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