Urologic Diseases Research Updates
Summer 2011

Cranberry Juice Fails to Prevent Recurrence of Urinary Tract Infections

Photo of a glass of cranberry juice and cranberries around the glass on a table.

Two glasses of cranberry juice per day failed to prevent the recurrence of urinary tract infections (UTIs) in a study funded by the National Center for Complementary and Alternative Medicine, part of the National Institutes of Health. The study is the largest to test the effectiveness of cranberry juice in preventing recurrent UTIs among otherwise healthy college-aged women.
“Laboratory analyses, observational studies, and a few small or open randomized trials suggest that regularly drinking cranberry juice decreases the risk of UTI,” wrote Cibele Barbosa-Cesnik, M.D., M.P.H., a research investigator at the University of Michigan School of Public Health, and co-authors in a report that appeared in the January 2011 issue of Clinical Infectious Diseases. Lacking, however, were double-blinded, randomized, placebo-controlled trials of otherwise healthy women. The study focused on college-aged women because they are at higher risk for UTIs.
UTIs are common in women and are treated with antibiotics. Bacteria, usually Escherichia coli, invade the urethra causing painful urination. Left untreated, UTIs can spread to the bladder and kidneys. About 24 percent of UTIs recur within 6 months, despite treatment with antibiotics.
According to Barbosa-Cesnik and co-authors, “treating UTI with antibiotics selects for antibiotic resistance among uropathogens and other bacteria found in and on the human body,” suggesting a great need for alternative therapeutic strategies.
The study enrolled more than 300 college women, ages 18 to 40, with a confirmed UTI. After successful antibiotic treatment, half the women were randomly assigned to one of two groups and monitored for 6 months or until the UTI recurred. One group drank 8 ounces of cranberry juice twice per day. The other group drank 8 ounces of a similar placebo juice lacking cranberry twice per day. During the study, neither the participants nor the investigators knew which juice participants were drinking.
Women in the study completed questionnaires regarding factors associated with UTIs, such as sexual activity and gastrointestinal illness, and reported any occurrence of UTI symptoms. Suspected UTIs were confirmed through bacterial culture.
Results of the study showed the cranberry and placebo juice groups had similar UTI recurrence rates. Surprisingly, the placebo juice group had a slightly lower recurrence rate than the cranberry juice group. “Contrary to expectation, we found that drinking an 8-ounce dosage of cranberry juice twice per day gave no protection against the risk of recurring UTI among college-aged women,” wrote Barbosa-Cesnik and co-authors.
Overall, UTI recurrence was about 17 percent lower than expected. “It is possible that the placebo inadvertently contained the active ingredient(s) in cranberry juice,” wrote the authors. The anti-UTI ingredient in cranberry juice remains unknown. Ascorbic acid is one possible active ingredient and, according to the authors, was present in both the cranberry and placebo juices.
Another explanation for the lower than expected overall UTI recurrence rate, stated the authors, is that participants may have been better hydrated. According to the National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC), drinking plenty of water can help prevent UTIs.
For more information about the cranberry juice trial, search for NCT00128128 at http://www.clinicaltrials.gov/.
For more information about UTIs and other urologic diseases, visit the NKUDIC, part of the National Institute of Diabetes and Digestive and Kidney Diseases, at http://www.urologic.niddk.nih.gov/.

NIH Publication No. 11–5743
September 2011