Updated on September 23, 2022
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THURSDAY, Sept. 30, 2004 (HealthDayNews) -- Patients with urinary tract infections (UTIs) often are told to drink cranberry juice to prevent future bladder problems. The advice is rather vague, since there's no data to show how much of the tart beverage people should drink for prevention's sake.
Now there's preliminary evidence to suggest that drinking more is better than drinking less, according to a pilot study being presented Oct. 1 at the annual meeting of the Infectious Diseases Society of America in Boston.
Tannins contained in cranberries interact with the tiny, hair-like protrusions on E. coli bacteria, the most common cause of UTIs. The infection-causing bacteria loose their stickiness and, instead of adhering to the walls of the bladder and causing infection, get washed away in urine.
In the study, researchers found that drinking eight ounces of the juice resulted in a 71 percent reduction in the amount of E. coli bacteria sticking to the bladder walls; a four-ounce serving produced a 33 percent reduction in the unwanted bacteria.
"Eight did basically twice as well as four," said lead investigator Dr. Kalpana Gupta, an assistant professor of medicine/infectious diseases at Yale University School of Medicine.
Two ounces of cranberry juice, however, had no effect in preventing E. coli adherence, she noted. "In our study, it seems here, at least four ounces are needed," said Gupta, who conducted the research when she was with the University of Washington, Seattle, with funding primarily from a National Institutes of Health career development award.
The preventive effect of cranberry juice appears to be dose-dependent. On that finding, researchers have already launched a larger study that will involve many more subjects and compare several different doses of juice.
Even at this preliminary stage, the information gives doctors at least a hint about what to tell their patients with UTIs. "There appears to be no standard amount of cranberry juice recommended, so the information from this study that 'more is better' is useful," said Dr. James Cummings, professor and chief of the division of urology at St. Louis University School of Medicine.
Further research into the cranberry connection could help the millions of Americans who suffer from UTIs, particularly women, who are more prone to getting them. UTIs accounted for more than 8 million doctor visits in 1997, according to the latest data from the National Kidney and Urologic Diseases Information Clearinghouse.
Most people with UTIs experience symptoms, such as a frequent urge to urinate and a painful burning during urination. The problem is treated with antibacterial drugs. For women with recurrent infections, doctors may recommend that they drink plenty of water, urinate when they have the urge, cleanse the genital area before intercourse, and take showers instead of baths to prevent future infections. And some doctors suggest drinking cranberry juice.
Researchers tested cranberry dosing by collecting urine from three symptom-free volunteers before they consumed pre-determined amounts of cranberry juice and four to six hours afterward. The juice they used was a 27 percent cranberry juice cocktail, the kind commonly found on grocery shelves.
Then the investigators incubated E. coli in the urine samples and combined it with human bladder cells to test how well cranberry juice would prevent the bacteria from sticking to those cells. Eight ounces of juice had a twofold greater effect than four ounces.
Does that mean UTI sufferers should drink up? "It's too early to give any advice," Gupta concluded.
Review studies involving mostly healthy young women have shown that cranberry juice may be effective, she said. But it's still not clear exactly how much juice is beneficial, how often UTI sufferers should drink it to prevent recurrences, whether it's effective in other populations, or which juice products contain the appropriate amount of the active tannin needed to prevent infection.
The National Center for Complementary and Alternative Medicine (NCCAM), a unit of the National Institutes of Health, is funding a series of studies that promise to help answer some of those questions. Gail D. Anderson, a professor at the University of Washington School of Pharmacy, is leading one of those studies, which will examine whether cranberry juice interacts with antibiotics used to treat UTIs. Other NCCAM-funded studies will examine efficacy and other safety issues.
Gupta's paper is the first of hopefully many studies to further determine the optimal dosing and efficacy of cranberry juice cocktail, Anderson said.
For now, Gupta suggested that people seeking to prevent UTIs discuss drinking cranberry juice with their doctor.
Consuming too much of the tart stuff isn't really a worry, since most health professionals say cranberry juice is safe. But tolerability is an issue, Anderson noted: "Not everyone likes the taste of cranberry juice."
Visit the National Kidney and Urologic Diseases Information Clearinghouse for more information on urinary tract infections.
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