Two-week cranberry course gives six months protection against bladder infections

Women who are susceptible to cystitis can improve their resistance by eating 42 g dried cranberries daily, write urologists and nutritionists at the University of Wisconsin in Nutrition Journal. A two-week course will have a six-month effect.
Women who are susceptible to cystitis can improve their resistance by eating 42 g dried cranberries daily, write urologists and nutritionists at the University of Wisconsin in Nutrition Journal. A two-week course will have a six-month effect.

Cranberry is a tried and tested remedy for urinary tract infections. The theory goes that it’s the phenols in cranberries, such as trans-cinnamaldehyde [structural formula shown here], that weaken bacteria, making it more difficult for them to attach themselves to the wall of the bladder. [J Urol. 2011 Apr;185(4):1526-31.] [BMC Microbiol. 2008 Sep 16;8:149.] [PLoS One. 2011 Jan 13;6(1):e16084.]

This theory still holds, but recent meta-studies have concluded that a course of cranberries only reduces the chance of an infection by ten to twenty percent. [Cochrane Database Syst Rev. 2012 Oct 17;10:CD001321.] That’s not much.

One factor that plagues these studies, however, is the high dropout rate. It seems that people find it difficult to sustain cranberry consumption over a longer period. Studies in which cranberry supplements were used instead have not been an unqualified success either – possibly because these supplements contain too small amounts of active ingredients.

This is the background against which the study was published in Nutrition Journal. It was financed by Ocean Spray Cranberries, the supplier of sweetened and dried cranberries that the researchers gave to 20 women who suffered from repeated urinary tract infections.

The researchers got the women to eat 42 g cranberries daily for two weeks. They then monitored the women for six months, noting when the women had an infection. The figure on the left below shows that most of the women had fewer infections in the six months after the cranberry course [6 month UTI-Rate] than in the six months preceding the treatment.


The figure on the right above shows that the women in the experimental group were less likely to develop an infection than the women in the control group. Half of the women in the experimental group remained infection free in the six months after taking the cranberries.

The researchers took samples of the bacteria in the women’s rectum and analysed them. They expected that the cranberries would have reduced the amount of bacteria that cause urinary tract infections, but they found no relevant effects.


The researchers suspect that cranberries contain bioactive substances that strengthen women’s immune systems, enabling them to better fight harmful bacteria. Animal studies have shown this to be the case. [JPEN J Parenter Enteral Nutr. 2014 Jan-Feb;38(1):107-14.] There is also a human study – funded by Ocean Spray – in which cranberries had a protective effect against viruses.

“The results of this study indicate a potential beneficial effect of consuming sweetened, dried cranberries in reducing the number of recurrent urinary tract infections in susceptible women”, the researchers conclude. “However, the results shown here are only preliminary and further studies are necessary. Daily sweetened, dried cranberry consumption is an inexpensive and readily available supplement to a woman’s diet and may provide potential prophylactic effects.”

Consumption of sweetened, dried cranberries may reduce urinary tract infection incidence in susceptible women – a modified observational study.

Burleigh AE, Benck SM, McAchran SE, Reed JD, Krueger CG, Hopkins WJ.



Urinary tract infections (UTIs) are one of the most common bacterial infections, and over 50% of women will have a UTI during their lifetimes. Antibiotics are used for prophylaxis of recurrent UTIs but can lead to emergence of drug-resistant bacteria. Therefore, it is reasonable to investigate nutritional strategies for prevention of UTIs. Cranberry juices and supplements have been used for UTI prophylaxis, but with variable efficacy. Because dried cranberries may contain a different spectrum of polyphenolics than juice, consuming berries may or may not be more beneficial than juice in decreasing the incidence of UTIs in susceptible women. The primary objectives of this study were to determine if consumption of sweetened, dried cranberries (SDC) decreases recurrent UTIs and whether this intervention would alter the heterogeneity, virulence factor (VF) profiles, or numbers of intestinal E. coli.


Twenty women with recurrent UTIs were enrolled in the trial and consumed one serving of SDC daily for two weeks. Clinical efficacy was determined by two criteria, a decrease in the six-month UTI rates pre- and post-consumption and increased time until the first UTI since beginning the study. Strain heterogeneity and virulence factor profiles of intestinal E. coli isolated from rectal swabs were determined by DNA fingerprinting and muliplex PCR, respectively. The numbers of intestinal E. coli eluted from rectal swabs pre- and post-consumption were also quantified.


Over one-half of the patients did not experience a UTI within six months of SDC consumption, and the mean UTI rate per six months decreased significantly. Kaplan-Meier analysis of infection incidence in women consuming SDC compared to patients in a previous control group showed a significant reduction in time until first UTI within six months. The heterogeneity, VF profiles, and prevalence of intestinal E. coli strains were not significantly different after cranberry consumption.


Results of this study indicate a beneficial effect from consuming SDC to reduce the number of UTIs in susceptible women. Because there were no changes in the heterogeneity or VF profiles of E. coli, additional studies are needed to determine the mechanism of action of SDC for reduction of UTIs.

PMID: 24139545 [PubMed – in process] PMCID: PMC3853585

Source: http://www.ncbi.nlm.nih.gov/pubmed/24139545

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