Oral preparations available in various forms—juice, capsules, tablets, powder
Utilises proanthocyanidins within cranberry to prevent bacteria sticking to the bladder lining
Various trials on the effectiveness of cranberry do not uniformly support which type of cranberry product to use
Cochrane review 2012 showed no significant benefit in preventing recurrent UTIs, which superseded the 2008 Cochrane review which did show significant benefit
Huge variability within studies cast doubt on the reliability of the conflicting Cochrane reviews—Therefore Cranberry may still be helpful in preventing uncomplicated UTIs in women
6.1 Introduction and Mechanism of Action
Cranberry is grown from the shrub Vaccinium Macrocarpon and throughout history, its various forms has been investigated for its’ potential to prevent UTIs. Formulations are varied, from juice to tablets, capsules and powder.
Within cranberry contains proanthocyanidins. Pathogens that cause UTIs often contain P-fimbriae on their surface to help them stick to the lining of the bladder and invade. Proanthocyanidins in theory bind to the P-fimbriae on the surface of uropathogens, in particular E. coli, thus inhibiting the bacteria’s ability to stick to the inner epithelial cell lining of the bladder wall.
Studies in both in vitro [1, 2] laboratory tests and in in vivo [3, 4] animals studies have shown a dramatic decrease in bacterial loads when treated with cranberry or a proanthocyanidin derivative and thus opened the door to the introduction of this treatment into clinical practice.
6.2 Clinical Evidence
There have been two Cochrane reviews on Cranberry use in preventing UTIs. Twenty-four trials with 4473 patients overall were investigated in the 2012 review which concluded that there were no significant benefit between cranberry product use and placebo. [Relative risk reduction of 0.86 (95% CI 0.71–1.04).] This was the case in elderly, pregnant women, cancer patients and patients with spinal cord injuries or neuropathic bladders .
However the 2008 Cochrane review superseded by the 2012 review actually found a benefit with cranberry products in preventing UTI recurrence. This study included ten trials and found a relative risk reduction of 0.65 (95% CI 0.46–0.90) .
However it is worthwhile noting that within each cranberry trial analysed for the Cochrane review showed a lack of standardisation in the type of cranberry product used. High dropout rates were also seen, especially in studies investigating cranberry juice where patients found consuming large volumes of cranberry juice difficult and therefore could not complete the study.
Finally the population of patients on which the conclusions were based were hugely varied. These studies included complex patients with underlying conditions including neuropathic bladders, spinal cord injury and previous radiotherapy as well as elderly patients and children. On the other hand, the early studies on Cranberry were in uncomplicated UTI groups, in particular women who were otherwise healthy.
Later studies started then to investigate the effect of cranberry in preventing UTIs in increasingly heterogeneous groups of patients.
In the 2012 Cochrane review, 30.3% of the total weight to the calculation of overall risk reduction was from patients with neuropathic bladders or spinal injuries and radiotherapy patients. Only 24.5% were contributed by results from healthy women with recurrent UTIs . This might explain the discrepancy between the earlier and later Cochrane reviews.
Overall, because of the 2012 Cochrane review, the current guidelines from National Institute of Clinical Excellence UK (NICE) do not list Cranberry products as a treatment or prevention for UTIs and the current European Association of Urology (EAU) guidelines states “no recommendation for use can be made”.
However the huge variability within all the studies mentioned above means further assessment into the discrepancy between the two high profile meta-analyses is required. The confusion on whether Cranberry (proanthocyanidins) treatment is or is not effective has meant medical professionals still often suggest cranberry as a prophylaxis, especially in uncomplicated cases of recurrent UTIs in women.