Cranberry benefits not an old wives’ tale

Consuming cranberry products can reduce the risk for urinary tract infections (UTIs), particularly in women, a meta-analysis shows.

Pooled quantitative data from nine trials, including 1175 individuals, showed that cranberry consumption could reduce the risk for UTIs by 38% overall and by 51% in women.

"Cranberry-containing products tend to be more effective in women with recurrent UTIs, female populations, children, cranberry juice drinkers, and people using cranberry-containing products more than twice daily," say Chien-Chang Lee (National Taiwan University Hospital, Yunlin) and colleagues.

The authors looked at 13 studies in total, including 1616 individuals, which assessed the effects of drinking cranberry juice or taking cranberry capsules or tablets. In most of the studies, participants took the products for 6 months.

In the 10 studies that assessed cumulative UTI incidence, nine were included in the final analysis. This showed that, as well as reducing the risk for UTI in the population as a whole, cranberry consumption also helped prevent infections in women with recurrent UTIs, reducing the risk by 47%.

These results are particularly noteworthy as men rarely contract UTIs, except in old age. By contrast, 40-50% of women will experience at least one episode during their lifetime, of which 20-30% will become recurrent.

The authors found that cranberry juice was more effective than cranberry capsules or tablets. They suggest that this could be due to better hydration in those taking juice, or that there might be an unidentified substance within cranberry juice that is not found in cranberry capsules. However, they note that capsules may be more appropriate for diabetes patients avoiding sugar or for preventing the gastrointestinal side effects of consuming large volumes of juice.

The authors highlight that the interpretation of their results is limited by several factors. The products used in the trials differed significantly in form, dosage, and A-type proanthocyanidin (PAC) content, and not all studies reported the daily dose. Furthermore, the trials varied in their definitions of UTI.

The mechanism by which cranberry consumption can prevent UTIs is unknown. However, PACs have been found to prevent the adherence of Escherichia coli to the urogenital mucosa. Only three of the trials in the meta-analysis reported PAC content and the authors suggest that in future PAC contents should be specified in trials to differentiate their effects.

They also call for more dose-response studies to determine optimal dosing. One such study is currently underway.

The authors conclude in the Archives of Internal Medicine: "The results of the present meta-analysis support that consumption of cranberry-containing products may protect against UTIs in certain populations. However, because of the substantial heterogeneity across trials, this conclusion should be interpreted with great caution."

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