Cranberry may help prevent UTIs

Cranberry-containing products appeared to reduce urinary tract infections (UTIs) in susceptible populations, a new meta-analysis found.

The review was intended as an update of a 2008 Cochrane review that had found favorable effects from cranberry juice. Searching MEDLINE, EMBASE and the Cochrane Central Register, the authors found a number of randomized controlled trials of cranberry-containing products for preventing UTIs published since the last review, which they analyzed together with older trials. In total, the analysis included 10 trials, with about 1,500 participants.

Cranberry users had a 38% lower risk of UTI compared to nonusers (random-effects pooled risk ratio [RR], 0.62; 95% CI, 0.49 to 0.80), the analysis found, with a moderate degree of heterogeneity among trials (I²=43%). Some subgroups appeared to benefit more from cranberry consumption, including women with recurrent UTIs (risk ratio [RR], 0.53; 95% CI, 0.33 to 0.83), women generally (RR, 0.49; 95% CI, 0.34 to 0.73) and children (RR, 0.33; 95% CI, 0.16 to 0.69). The results were published in the July 9 Archives of Internal Medicine.

Cranberry juice appeared to be more effective than capsules or tablets (RR for juice drinkers, 0.47; 95% CI, 0.30 to 0.72), although researchers noted some potential limitations of this finding. While the effect might come from some additive or synergistic effect of a substance in the juice, it might also be that the juice drinkers were better hydrated than other cranberry consumers. In addition, consuming a large quantity of sugared cranberry juice might be problematic for diabetic patients, the authors noted.

Frequent consumption of cranberry appeared to improve effectiveness; relative risk was 0.58 for participants who consumed the products more than twice daily (95% CI, 0.40 to 0.84). The analysis was not able to determine the most effective dose of cranberry, however. Included trials had a wide variation in the proanthocyanidin (PAC) content of their cranberry products. Researchers called for specification of PAC content in future trials and on cranberry products.

Another limitation of the study was that an outlier study had to be excluded in order to show a significant effect of cranberry products. With that study included, the overall risk ratio associated with cranberry consumption would have been 0.68 with a 95% CI of 0.47 to 1.00. The outlier trial used a lower bacteruria threshold and had a much lower overall incidence rate of UTI. In conclusion, the analysis authors said that consumption of cranberry products may protect certain populations against UTIs, but they urged that results be interpreted cautiously, given the heterogeneity of the trials.