Cranberry juice fails to prevent recurrent urinary tract infection

Researchers at the University of Michigan School of Public Health, in Ann Arbor, recorded the effects in college women presenting with an acute urinary tract infection (UTI).

First, the details.

  • 319 college women presenting with an acute UTI were assigned to a treatment group and followed until a second UTI or for 6 months, whichever came first.
    • A cranberry treatment group: drinking 8 oz of 27% cranberry juice twice daily
    • A placebo group
  • UTI was defined on the presence of symptoms and a urine culture positive for a known pathogen.
  • The study was designed to detect a 2-fold difference between treated and placebo groups.
  • The researchers assumed 30% of participants would experience a UTI during follow-up.
  • Neither the patients nor researchers knew the treatment given — double blind.

And, the results.

  • Overall, the recurrence rate was 17%.
  • Distribution of recurrence was similar between treatments.
  • The cranberry group had a slightly higher recurrence rate (20% vs 14%).
  • The presence of urinary symptoms at all times during the study was similar between treatments, with overall no marked differences.
  • Adjusting for the frequency of sexual activity in the previous month and a history of UTI made no difference in the risk of recurrence by treatment.

The bottom line?

The authors concluded, “Among otherwise healthy college women with an acute UTI, those drinking 8 oz of 27% cranberry juice twice daily did not experience a decrease in the 6-month incidence of a second UTI, compared with those drinking a placebo.

Regarding other studies that reported positive results with cranberry juice, the authors counter that “these studies were not blinded or were underpowered (insufficient participants to detect a real difference).”

Other categories of patients have been studied, and many of the results are summarized here.

This study was supported by a grant from the National Center for Alternative Medicine at the National Institutes of Health.

1/20/11 20:34 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.