Drinking eight ounces of cranberry juice works better than four in combating urinary tract infections

Cranberry juice has long been recommended to ward off bladder infections: Now there's evidence that more of the tart drink may be better than less. Drinking eight ounces of the juice works better than four in combating the bacteria that cause most urinary tract infections (UTI), according to preliminary research being presented at the 42nd Annual Meeting of the Infectious Diseases Society of America (IDSA).

  • Drinking eight ounces of cranberry juice cocktail at a time may be better than four if you're trying to ward off a bladder infection, suggests a study.
  • Cranberries contain a substance that prevents urinary tract infections by stopping bacteria from sticking to the wall of the bladder.
  • Native Americans used cranberries to treat urinary disorders.

A specific type of tannin found only in cranberries and blueberries interacts with the little projections on the Escherichia coli (E. coli) bacteria (the most common cause of UTI), preventing them from sticking to the walls of the bladder and causing infection.

A UTI is an infection anywhere in the urinary tract, including the kidneys, the bladder and the urethra. Due to anatomy, women have a higher risk of UTIs than men, and people who experience three or more in one year are considered to have recurrent infections.

"There is no evidence that drinking or eating cranberry products can cure a UTI once the bacteria have established infection," said Kalpana Gupta, MD, principal investigator of the University of Washington study. "The next step is to evaluate our findings in a larger group of women, and then conduct a trial to help determine if the laboratory findings translate into clinical differences in the rate of UTI depending on the dosage of cranberry consumed."

Theoretically, blueberries may prevent UTIs as well, but they need to be further tested in a laboratory and clinical trials, she said.

"Cranberry is one of North America's few native fruits, and Native Americans used it for its antibacterial properties," said Amy Howell, PhD, coauthor of the study and a research scientist at the Marucci Center for Blueberry and Cranberry Research at Rutgers University, Chatsworth, N.J. "They even mention it for urinary disorders."

In the study, urine was collected from three volunteers before and four to six hours after consumption of 27-percent cranberry juice cocktail. E. coli were incubated in the urine samples and combined with human bladder cells. The amount of bacteria sticking to the bladder cells was significantly reduced after the bacteria were incubated in urine from women who drank the cranberry juice cocktail, and that effect was two-fold greater after eight ounces of cranberry juice cocktail was consumed than after four ounces was consumed.

The length of time that the activity lasts, the magnitude of activity with additional doses, and the effects of concurrent food ingestion on the laboratory activity are currently being studied under funding provided by the National Center for Complementary and Alternative Medicine of the National Institutes of Health, notes Dr. Gupta.

"It is unlikely that regularly consuming a glass of cranberry juice has a downside, but this will be formally evaluated in future clinical trials," said Dr. Gupta, now assistant professor of medicine at Yale University, New Haven, Conn.

Women who feel symptoms (including a frequent need to urinate, and pain or burning after urination) should see their health care providers, and if diagnosed with a bladder infection, should receive antibiotics, said Dr. Gupta. Untreated, a bladder infection can become a more serious kidney infection.

Combinations of cranberry and other fruit juices (such as apple, grape and raspberry) contain a smaller percentage of cranberry juice and may be less effective for UTI prevention, but have not been adequately studied, said Dr. Gupta.

Cranberry tablets also may vary in the percentage of the effective tannin, and therefore may or may not help prevent UTIs. Tablets that include spray-dried cranberry juice include the tannin, while those that are derived from various extracts may not, said Dr. Howell. Initial studies suggest that single serving sizes of dried cranberries and cranberry sauce contain as much of the tannin as a serving of cranberry juice cocktail, and may be just as effective as the juice.

In addition to Drs. Gupta and Howell, co-authors of a paper on the topic being presented at IDSA include Walter E. Stamm, Cheryl L. Wobbe and Ann E. Stapleton.

IDSA is an organization of physicians, scientists and other health care professionals dedicated to promoting human health through excellence in infectious diseases research, education, prevention and patient care. Major programs of IDSA include publication of two journals, The Journal of Infectious Diseases and Clinical Infectious Diseases, an Annual Meeting, awards and fellowships, public policy and advocacy, practice guidelines and other membership services. The Society, which has 7,500 members, was founded in 1963 and is headquartered in Alexandria, Va.

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