“A urinary tract infection (UTI) is common and increasingly difficult to treat because of the rising rates of antibiotic resistance,” wrote researchers in a new study published in The American Journal of Clinical Nutrition.
They expanded on existing literature, mostly randomized clinical trials that suggest a benefit of UTI prevention, but deemed the results were still conflicting. Thus, their study compared the effects of the consumption of a cranberry beverage with that of a placebo “on the clinical (symptomatic) UTI incidence density in healthy women with a recent history of a UTI,” they wrote.
Two of the researchers are employees of Ocean Spray, manufacturer of the cranberry juice used in the study. The company also provided funding for the study.
The beverages used
A total of 373 women who met the eligibility criteria participated in the study. Participants were required to have a recent history of a UTI (more than two the previous year) that was treated by a health care professional in the past year. The multi-location trial included participants in the US, France, and Spain.
Of these participants, 185 women were assigned cranberry juice, and the remaining 188 were assigned the placebo beverage. The latter was designed to look, smell, and taste like the cranberry beverage, but lacked the anthocyanins, phenolic acids, and flavanols of the cranberry juice.
“The cranberry juice cocktail study beverage used was similar to commercially available low-calorie products in its juice content (27% cranberry juice),” the researchers wrote.
The subjects were required to avoid consumption of Vaccinium products other than the assigned dose of cranberry juice or placebo. This also included avoiding blueberries and any other product in any format derived from blueberries or cranberries. They were also asked to refrain from consuming probiotic-containing products for the study’s 24-week duration, as well as two weeks prior to initial screening.
The researchers observed a 39% reduction in clinical UTI episodes, measured through a validated daily diary in which participants recorded their consumption of the study beverage and recorded any UTI symptoms.
Focused in this study was the clinical UTI incidence density, defined as the number of clinical UTI events in each group per unit of observation time. “In conclusion, the consumption of a cranberry juice beverage significantly reduced the clinical UTI incidence density in women with a history of [more than] two UTIs in the previous year,” they said.
However, some parties took issue with the researcher's primary focus on symptomatic UTI. "By this much looser measure, the two groups indeed differed, and in a way that favored drinking cranberry juice: There were 39 episodes of symptomatic UTIs in the cranberry group compared with 67 episodes in the placebo group," reported Senior Health Correspondent Julia Belluz in a scathing critique of the study published on Vox Science and Health.
“Previous clinical trials on cranberries and UTI prevention have yielded conflicting results, but the majority of the negative studies used cranberry products that may not have had sufficient efficacy as they were not standardized for active PAC content,” Dr. Amy B. Howell, associate research scientist at the Marucci Center for Blueberry Cranberry Research at Rutgers University, told NutraIngredients-USA.
“This latest study utilized a cranberry juice formulation that was highly standardized for PAC level and exhibited bioactivity. Thus, I am not surprised that they demonstrated a significant reduction in the number of symptomatic UTIs when subjects consumed cranberry juice consistently,” she added.
Dr. Howell also recommended further research. “Additional clinical trials utilizing standardized cranberry products (juices, dried encapsulated powders) which seek to further define dose-response, mechanisms of action, and efficacy in different demographics will help to further elucidate the positive correlation between cranberry consumption and UTI prevention,” she said.
Source: The American Journal of Clinical of Nutrition
Published online ahead of print, doi: 10.3945/ajcn.116.130542
Author: Kevin C. Maki, et al.
UPDATES: A revision was made to add a quote from Julia Belluz' critical response published on Vox, as well as Ocean Spray's involvement in the study.