Ten randomized controlled trials included in the review determined that cranberry products reduced the annual incidence of UTIs by 39% in women with a history of recurrence, Ruth Jepson, of the University of Stirling, and Jonathan Craig, M.D., of the University of Sydney in Australia, reported in a Cochrane review.
For these women, cranberries demonstrated clear-cut infection-fighting, the investigators reported. The benefits in other groups were less certain.
"Overall, the evidence â€¦ indicates that cranberry products can be effective in reducing UTIs," the authors concluded. "However, it may only be effective in certain subpopulations."
"Furthermore, there is no clear evidence as to the amount and concentration that needs to be consumed, and the length of time for the intervention to be most effective," they added.
Moreover, most studies using cranberry juice had high dropout rates, suggesting that drinking considerable amounts of cranberry juice over a long period may not be acceptable. For this reason, the authors suggest that "further studies of cranberry capsules/tablets or other cranberry products, therefore, are also needed."
Cranberry products, usually juice, have been used for years as a nonprescription approach to prevention of urinary tract infections. Though almost 90% water, cranberries also contain quinic acid, malic acid, and citric acid, as well as glucose and fructose.
No definitive mechanism of action has been identified to explain cranberries' potential to ward off UTIs. The most common explanation is that cranberries prevent bacteria from adhering to the uroepithelium of the bladder, thereby blocking the ability of Escherichia coli to infect the urinary mucosa.
In an effort to clarify cranberry products' potential to prevent UTIs, the authors conducted a literature search to identify all randomized controlled trials of cranberry juice or other cranberry-containing products versus placebo, no treatment, or any other treatment. The search yielded 10 studies involving 1,049 participants.
In seven of the 10 studies, cranberry or cranberry/lingonberry juice was compared with placebo juice or water. Four studies evaluated cranberry tablets versus placebo (including one study that evaluated cranberry juice and tablets).
Overall, cranberry-derived products significantly reduced the 12-month incidence of UTIs versus placebo or control (relative risk: 0.65, 95% CI: 0.46 to 0.90). Cranberry products reduced the risk of UTI by 39% in women with a history of recurrent UTI (95% CI: 0.40 to 0.91). Studies of older men and women demonstrated a trend toward a beneficial effect, but the result did not achieve statistical significance (RR: 0.51, 95% CI: 0.21 to 1.22).
In patients with neuropathic bladder, cranberry treatment arms had a slight increase in the risk of UTI, but the difference was not significant (RR: 1.06, 95% CI: 0.51 to 2.21).
|The study was supported by the Nuffield Trust.
The authors declared no conflicts.
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine
Cochrane Database of Systematic ReviewsSource Reference: Jepson RG, Craig JC, "Cranberries for preventing urinary tract infections (review)" Cochrane Database Syst Rev 2008, Issue 1. Art. No.: CD001321. DOI: 10.1002/14651858.CD001321.pub4.