Writing in Clinical Infectious Diseases, University of Michigan researchers interpreted this data to conclude: “Contrary to expectation, we found that drinking an 8-oz dosage of cranberry juice twice per day gave no protection against the risk of recurring UTI among college-aged women.”
The trial was designed on the assumption of a 30 percent recurrence rate, while the actual recurrence rate from both groups - cranberry and placebo - averaged 16.9 percent.
Commenting on the study, Dr Amy Howell, a highly respected cranberry researcher, told NutraIngredients-USA.com that, despite the journal title stating that cranberry juice failed, in actual fact it did work. But so did the placebo. “The conclusions are just goofy,” she said.
“Because no statistically significant differences were observed between the placebo and the cranberry group (recurrence rate of 14.6 and 19.3 percent, respectively), the researchers concluded that the cranberry treatment was ineffective compared to the placebo,” explained Dr Howell. “The authors speculated that the placebo may have contained an active component that prevented UTIs.
“Although the study failed to detect a difference between the placebo and treatment groups (although twice as many gastrointestinal issues were reported in the placebo group), the students experienced fewer UTIs following the six-month period on both beverages.
“In accordance with the reported results, the findings do not support the conclusion that cranberry juice failed to prevent recurrent urinary tract infections, as the article title would suggest,” she added.
Compliant or not compliant?
Dr Howell also questioned the compliance of the participants - 319 college women with an average age of 21. The compliance was based on self-reporting by the participants.
Dan Souza, director of sales and marketing for Decas Botanical Synergies, echoed Dr Howell’s comments on compliance: “The problem with this study is that there is no ability to truly measure compliance in these college age women who were paid to participate,” Souza told NutraIngredients-USA.com
“How do the researchers know that their subjects were actually ingesting the cranberry? The cranberry industry is aware of this potential pitfall, and currently several lead researchers are working on identifying the metabolites such that true compliance can be measured,” he said.
“Also, the ability to drink two glasses daily for six months or more is difficult and all the more reason supplements such as PACran can be more effective,” he added.
The A, B, PACs of the study
The link between cranberries and urinary tract health is well established, and linked to its proanthocyanidin (PAC) content. However, according to the Michigan researchers, there is a “lack of adequately powered double-blind, randomized placebo-controlled trials of cranberry juice effectiveness in reducing risk of recurring UTI [and this] led us to conduct this study among college women presenting for treatment with acute urinary tract infection.”
The college women were randomly assigned to consume either 8 oz of 27 percent low-calorie cranberry juice cocktail twice a day (Ocean Spray Cranberries) or 8 oz of placebo juice twice a day. The placebo contained, amongst other things, vitamin C and a colorant.
At the end of the study, about 70 percent of women in the cranberry juice complied with the regime, compared with about 50 percent in the placebo group. Results showed an overall recurrence rate of 16.9 percent, said the researchers.
Commenting on the lack of difference between the groups, the researchers said: “It is possible that the placebo inadvertently contained the active ingredient(s) in cranberry juice. While the active ingredient was previously believed to be proanthocyanidin, and the placebo was tested accordingly, the actual active ingredient is uncertain.
“Both placebo and cranberry juice contained ascorbic acid, which has also been suggested to prevent UTI, but has not been demonstrated to reduce risk in controlled trials.
“Another possibility to explain our results is that our study protocol kept all participants better hydrated and led them to urinate more frequently, decreasing bacterial growth and/or reducing mild urinary symptoms,” they added.
One study versus many
Dr Howell commented that there are “numerous, positive studies on the benefits of cranberry consumption for urinary tract health.
“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,” she added.
In 2004 France became the first country to approve a health claim for the North American cranberry (Vaccinium macrocarpon) with at least 36mg of proanthocyanidins (PAC) to “help reduce the adhesion of certain E. coli bacteria to the urinary tract walls”, and subsequently fight UTIs.
PACs are not exclusive to cranberries, and can be found in a range of foods, including green tea, grapes, apples, and chocolate. However, the main type of PACs in cranberry called A-type PACs are different from those in these other sources, called B-type PACs. Only cranberry PACs may prevent bacterial adhesion.
Source: Clinical Infectious Diseases
2011, Volume 52, Issue 1, Pages 23-30. doi: 10.1093/cid/ciq073
“Cranberry Juice Fails to Prevent Recurrent Urinary Tract Infection: Results From a Randomized Placebo-Controlled Trial”
Authors: C. Barbosa-Cesnik, M.B. Brown, M. Buxton, L. Zhang, J. DeBusscher,B. Foxman
The study was funded by the National Center for Alternative Medicine at the National Institutes of Health.