Cranberry Juice, Placebo Equally Good at Preventing UTIs?
Although a new study found that drinking cranberry juice to prevent recurring urinary tract infections (UTIs) was no more effective than taking a placebo, there are questions about the validity of the findings. Numerous previous studies have found cranberry juice to be effective at preventing UTIs.
Can cranberry juice help prevent UTIs?
Researchers at the University of Michigan enrolled 319 college women (average age, 21 years) who had an acute UTI in a double-blind, placebo-controlled study to determine the risk of recurring infection. Urinary tract infections affect about 11 percent of all women 18 years or older each year in the United States, with peak incidence among women aged 18 to 24.
The women were randomly assigned to drink either 8 ounces of 27% low-calorie cranberry juice cocktail (Ocean Spray) twice a day (155 women) or 8 ounces of placebo juice twice daily. The placebo beverage was prepared by Ocean Spray to imitate the sweetness, acidity, and color of the cranberry beverage, but it did not contain any cranberry. Both beverages contained vitamin C.
The women were followed until they had a recurring UTI or for six months, whichever came first. Researchers depended on participants self-reports of compliance, which was about 70% in the cranberry juice group and 50 percent in the placebo group.
Although the researchers had assumed 30% of the participants would experience a recurring UTI during the study period, instead the rate averaged 16.9% in both groups: 14.6% among those who took placebo and 19.3% among women who drank the cranberry juice. The authors concluded that drinking cranberry juice twice daily “gave no protection against the risk of recurring UTI among college-aged women.”
Previous research has indicated that the ability of cranberries and cranberry juice to prevent UTIs is associated with its phytochemical content, including proanthocyanidins, flavonols, and phenolic acid. In 2004, France approved a health claim that the North American cranberry with at least 36 mg of proanthocyanidins can “help reduce the adhesion of certain E. coli bacteria to the urinary tract walls.”
Subsequent to France’s declaration, a mechanical study from Worcester Polytechnic Institute reported that cranberry juice works at a molecular level to prevent UTIs by reducing the ability of E. coli bacteria to cling to urinary tract cells. Information presented at a recent American Chemical Society meeting noted that cranberry juice may also help stop staph infections.
The University of Michigan researchers have several possible explanations for the lack of significant difference between the two groups in their study. One is that the placebo “inadvertently contained the active ingredient(s) in cranberry juice,” even though the placebo was tested.
The researchers also noted that both beverages in their study contained vitamin C, “which has also been suggested to prevent UTI, but has not been demonstrated to reduce risk in controlled trials.” They also suggest the study protocol may have kept the subjects more hydrated, which caused them to urinate more frequently, which in turn reduced bacterial growth as well as mild urinary symptoms.
According to Dr. Amy Howell, associate research scientist at the Marucci Blueberry and Cranberry Research and Extension Center, Rutgers University, there are “numerous, positive studies on the benefits of cranberry consumption for urinary tract health.” Howell and her team isolated proanthocyanidins from cranberries, and her work has appeared in the New England Journal of Medicine and the Journal of the American Medical Association.
In a NutraIngredients-USA article, Howell commented that “Given the body of evidence, if women are currently consuming cranberry products, the results of this one study do not provide a reason for them to change their current practices.” For many women, cranberry juice is still the way to prevent help UTIs.
Barbosa-Cesnik C et al. Clinical Infectious Diseases 2011; 52(1): 23-30
Cote J et al. Critical Reviews in Food Science and Nutrition 2010 Oct; 50(9): 872-88