12 January - 20 June 2016

Systematic review clarifies association between cranberry intake and urinary tract infection

A systematic review with meta-analysis published in the Journal of Urology by researchers in Portugal, has sought to clarify the association between cranberry intake and the prevention of urinary tract infections.

Urinary tract infections (UTI) are common among healthy women and it is estimated that around 20% to 30% of women who develop an infection will have a recurrent one within the following six months. Cranberries have often been proposed to have benefits in protecting against UTIs, thought to be due to their high concentration of polyphenols such as proanthocyanidins (PAC) in the berries. 

A systematic review with meta-analysis published in the Journal of Urology by researchers in Portugal, has sought to clarify the association between cranberry intake and the prevention of urinary tract infections.  Luis et al. carried out a literature search of studies regarding the effect of cranberries to prevent UTIs and identified 28 studies which they considered were suitable for qualitative and quantitative analysis involving 4949 patients.  Follow up in the included trials varied from 2 week to 12 months, with cranberries been ingested in a number of oral forms ranging from juices, capsules, tablets and extracts for different PAC doses with one study using a high dose of 240 mg PAC per day and a low dose of 80 mg PAC per day. 

Using numerous analysis, the authors estimated weighted risk ratios and report that there was a significant reduction in the risk of repeat UTIs with cranberry treatment compared to a placebo and using trial sequential analysis confirmed their findings.  They evaluated the influence of patient age, intervention duration and type on the effectiveness and note that whilst "there was evidence of benefit of cranberries in reducing UTIs overall, the subgroup analysis showed that compared with placebo, cranberries did not significantly decrease repeat UTIs in any of the subgroups."  This finding did not change even when they omitted a single study or a few studies.  The team discovered that for both genders incidence of UTIs was significantly decreased in the cranberry treated group.  Regarding age the scientists concluded that in children 2 to 17 years old and in middle-aged adults 36 to 55 years old cranberry ingestion significantly decreased the incidence of UTIs.  Those who had undergone gynaecological survey were found to be more protected by cranberry intake with a significant reduction in the UTIs in those groups. 

Luis et al. note that "although European Association of Urology recommends continuous use of cranberries as an alternative method to prevent UTIs, the data are not conclusive because the available studies were performed for periods of up to a year. Thus there is no evidence to support the efficacy of cranberry products for chronic use.  Future trials may need to cover much longer periods."  They continue by stating that the effectiveness of cranberry is probably dependent on the concentration of PAC which "are the polyphenols associated with the amelioration of UTIs.” They report that “the most accepted mechanism of action for prevention UTIs by cranberries is based on its interference with bacterial adhesion in the urinary tract.”  They continue by stating that cranberries “prevent uropathogenic P-fimbriated E. coli from adhering to bladder cell receptors".

RSSL can analyse food products for polyphenolic components. To find out more please contact Customer Services telephone 0118 918 4076 or e-mail enquiries@rssl.com

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