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Cochrane Collaboration Revises 2008 Conclusions on Cranberry for UTI Prevention: Experts, researchers clarify results from recent meta-analysis

Reviewed: Jepson RG, Williams G, Craig JC. Cranberries for preventing urinary tract infections (review). The Cochrane Library; 2012:10.

Urinary tract infections (UTI) are among the most common type of infection in adults and result in more than 8 million visits to healthcare providers annually. UTIs — which are 50 times more likely to occur in women — can arise in any part of the urinary tract, including the kidneys, bladder, or urethra, and are most frequently caused by bacteria such as E. coli. Currently, antibiotics are considered the most effective treatment for the infection, and some women who experience frequent UTIs are prescribed low-dose antibiotics as a preventative measure.1 With antibiotic resistance a growing concern in recent years, however, researchers are studying plant-based UTI prevention strategies, including formulations of American cranberry (Vaccinium macrocarpon, Ericaceae).

Cranberry has been a popular prophylactic for urinary tract infections for decades and has been used by indigenous North American peoples for centuries to treat certain urinary conditions.2 Since 1998, cranberry has been the focus of four major reviews from the Cochrane Collaboration, an independent research organization that advocates evidence-based decision-making in healthcare.3,4 Its popularity as a urinary tract health supplement, in part, helped make cranberry the best-selling single-herb supplement in the US Food, Drug, and Mass Market retail channel in 2011, commanding sales of more than $40 million.5

A 2008 Cochrane Review, which analyzed 10 studies of cranberry for the prevention of UTIs, concluded that cranberry products — such as juices or capsules — significantly reduced the occurrence of UTIs at 12 months, particularly in women with recurrent infections.6 An update of the review, published in October 2012, however, found that “there was a small [but insignificant] trend towards fewer UTIs in people taking cranberry products compared to placebo or no treatment.” Although the authors noted a number of potential weaknesses in the reviewed studies, they concluded that “until there are more studies of products containing enough of the active ingredient [emphasis added], measured in a standardised way, cranberry products cannot be recommended for preventing UTIs.”4

Unusually high dropout rates and methodological issues with many of the studies included in the 2012 review — such as failure to quantify the main active ingredient for UTI prevention in cranberry and small sample sizes — have led some to question the validity of the Cochrane group’s findings. 

“It is essential that cranberry continue to be regarded and researched as an important area of study to help address the public health challenge that urinary tract infections and their treatment presents to antibiotic resistance,” said Amy Howell, PhD, an associate research scientist at Rutgers University’s Marucci Center for Blueberry and Cranberry Research (email, November 27, 2012). “UTIs are a significant public health challenge with more than 15 million cases in the US each year, and their treatment accounting for 15 percent of all community-prescribed antibiotics. I think that cranberry has great potential to help slow the pace of resistance development in an era when consumers are concerned with having to rely on pharmaceuticals to prevent and treat disease. ”

Cranberries as a Preventative Measure

Fresh cranberries are composed of roughly 90 percent water and are known for their elevated concentration in total polyphenols, such as anthocyanins, tannins, flavonoids (flavonols and flavan-3-ols), and, most notably, proanthocyanidins (PACs). The amount of polyphenols in cranberry, however, comprises just a small percentage of the fruit’s total organic constituents. Previously, scientists believed that organic acid in cranberry acidified the urine, which acted as an antimicrobial agent. Current hypotheses revolve around a specific type of PACs — those with type-A linkages — that are thought to be responsible for the fruit’s ability to inhibit bacteria from sticking