Cranberry Juice May Not Prevent Urinary Tract Infection

Nancy Fowler Larson

December 16, 2010

December 16, 2010 — Drinking cranberry juice does not appear to ward off urinary tract infection (UTI) in young women, according to a study published in the January 2011 issue of Clinical Infectious Diseases.

One of the most common bacterial infections, UTI affects approximately 11% of all US women each year, with 1 in 5 infections affecting those 18 to 24 years old. Not only are antibiotic prevention plans and treatment of UTI expensive ($1.6 million in 1995 dollars), but they also contribute to drug resistance.

"Because antibiotic therapy is a major driver of resistance, and adversely affects the normal microbiota, preventive strategies that reduce the need for antibiotic therapy are particularly important," write Betsy Foxman, PhD, from the University of Michigan School of Public Health in Ann Arbor, and colleagues.

Relatively inexpensive cranberry juice is a folk remedy shown to be effective in preventing UTI recurrence in observational studies and in small or open randomized trials. Seeking more substantial evidence, the investigators launched a double-blind, placebo-controlled trial testing its impact on recurrent infections.

The researchers studied 319 otherwise healthy college women, with a mean age of 21 years, who were diagnosed with acute UTI at the Michigan Health Service laboratory between August 2005 and October 2007. They observed the participants for 6 months or until a second infection occurred and assumed that 30% of the women would experience another UTI during the observation period.

The subjects were randomly assigned to drink 8 ounces of 27% low-calorie cranberry juice cocktail (n = 155) or the same amount of a placebo juice (n = 164) at 2 times a day throughout the 6-month follow-up. Self-collected vaginal and rectal specimens and a clean-catch midstream urine specimen were presented by the women at baseline and at 3 months and 6 months. These were cultured to determine the presence of uropathogens.

Information about UTI and other symptoms, risk factors for infection, diet, and other factors was collected at various times during the trial through on-site questionnaires, telephone interviews, and online surveys.

Cranberry Juice Drinkers Had Higher UTI Recurrence

At the study’s conclusion, 230 (72%) of the women had completed the full protocol. Self-reported compliance was similar between the cranberry juice group and the placebo group. Pertinent findings, adjusted for sexual activity and UTI history, are as follows:

  • Among all participants, the recurrence rate was 16.9% (95% confidence interval [CI], 12.8% - 21.0%).

  • The group drinking cranberry juice had a slightly higher recurrence rate (20.0% vs 14.0%).

  • Symptoms reported by the participants at 3 days, 1 to 2 weeks, and at 1 month or longer were similar between the groups.

Among those with 2 or more previous UTIs, the risk for occurrence was significantly greater (22% vs 10%; P = .0007), but cranberry juice had no significant impact on those with or without such a history.

Rebecca Kolp, MD, an obstetrician-gynecologist at Massachusetts General Hospital in Boston, has never recommended cranberry juice to patients with UTI. Dr. Kolp told Medscape Medical News that she was not surprised by the findings.

"I've heard a lot of people say they feel cranberry juice helps, but there was never any scientific proof," Dr. Kolp said. "I think there are a lot of other preventative steps they can take such as staying well hydrated and urinating after intercourse."

The investigators acknowledged 3 possible limitations to their study:

  • The placebo may have unintentionally contained the active ingredients in cranberry juice, as the exact ingredients have not been isolated with full certainty.

  • Cranberry juice and the placebo both contain ascorbic acid, which is suggested to reduce the risk for UTI, an association that has not been found in controlled trials.

  • Because the study prescribed liquids, participants may have experienced better hydration than usual, and their more frequent urination may have stunted bacterial growth and decreased mild UTI symptoms.

A strength of the study, according to Andrew Steele, MD, professor of urogynecology at Saint Louis University School of Medicine, in St. Louis, Missouri, is its reliable diagnostics, which exceeded symptoms assessment by culturing specimens.

"When you deal with recurrent urinary tract infection in women, the first question you've always got to always ask yourself is, 'Is this really an infection?'" Dr. Steele said. "There are a lot of other things that can cause infection symptoms."

The researchers noted that their findings are similar to those of 2 previous studies: one, whose 305 subjects had a neuropathic bladder after a spinal cord injury, and another whose participants were much older than the population in which UTI most often occurs.

"Of interest, in the only other large trial of cranberry juice compared with placebo juice, conducted among 376 British inpatients ≥60 years, the incidence of symptomatic UTI was also lower than anticipated in the placebo group, but there was no significant difference between groups," the study authors write.

The National Institutes of Health supported the study. The study authors, Dr. Kolp, and Dr. Steele have disclosed no relevant financial relationships.

Clin Infect Dis. 2011;52:23-30. Abstract

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