Cranberry Products May Prevent Urinary Tract Infections

Troy Brown

July 09, 2012

July 9, 2012 — Cranberry-containing products may protect against urinary tract infections (UTIs), according to a recent meta-analysis. However, because there was substantial heterogeneity among the studies, the results of the analysis should be viewed with caution, the researchers say.

Chih-Hung Wang, MD, from the Department of Emergency Medicine at National Taiwan University Hospital and National Taiwan University College of Medicine in Taipei and colleagues report their findings in the July 9 issue of the Archives of Internal Medicine.

One of the most common bacterial infections, UTIs affect up to 40% to 50% of women at least once in their lifetimes, the authors report. Pregnant women, the elderly, and patients with neuropathic bladder are also at increased risk for developing UTIs.

Cranberry (genus Vaccinium, including the species V oxycoccus, V macrocarpon, V microcarpum, and V erythrocarpum) is a folk remedy that has been used for years to relieve UTI symptoms. Cranberry was originally thought to work by acidifying the urine, but its effects are now known to be due to its interference with the attachment of bacteria to uroepithelial cells. In fact, A-type proanthocyanidins were identified in cranberry in 1989 as compounds with the potential to inhibit the adherence of P-fimbriated Escherichia coli to the urogenital mucosa.

Several new studies have been published since the last meta-analysis on this issue. Therefore, Dr. Wang and his team wanted to reevaluate the effectiveness of cranberry products for preventing UTIs and to study factors that influence their effectiveness.

Dr. Wang and colleagues analyzed 10 trials with a total of 1494 participants (794 in the cranberry groups and 700 in the control groups) in the meta-analysis. Significant heterogeneity was found among trials (relative risk [RR], 0.68; 95% confidence interval [CI], 0.47 - 1.00) (I2 = 59%). One trial was excluded from the main analysis because it had the most significant effect on the pooled summary estimate.

Cranberry Products Appear Effective

Heterogeneity decreased after exclusion of this trial, and cranberry-containing products appeared to effectively prevent UTIs (RR, 0.62; 95% CI, 0.49 - 0.80) (I 2 = 43%).

According to sensitivity analysis, the pooled summary estimate was stable to risks of bias in random sequence generation, study characteristics, and definitions of UTI, but the protective effect was much stronger in 2 studies that didn't use placebo in the control group (pooled RR, 0.36; 95% CI, 0.21 - 0.62).

Certain Populations Seem to Benefit More

Subgroup analysis found that some populations seemed to experience higher protective effects, including women with recurrent UTIs (RR, 0.53; 95% CI, 0.33 - 0.83) (I 2 = 0%), female populations (RR, 0.49; 95% CI, 0.34 - 0.73) (I 2 = 34%), children (RR, 0.33; 95% CI, 0.16 - 0.69) (I 2 = 0%), cranberry juice users (RR, 0.47; 95% CI, 0.30 - 0.72) (I 2 = 2%), and people using cranberry-containing products more than twice daily (RR, 0.58; 95% CI, 0.40 - 0.84) (I 2 = 18%). The findings, though, were not statistically significant in meta-regression.

Cranberry juice was more effective than cranberry capsules. The authors write that this could be due to increased hydration from drinking the juice or the effects of unknown substances in the juice. The authors acknowledge that drinking large quantities of juice could be problematic for some individuals, including patients with diabetes and those with gastrointestinal issues.

A dosing frequency of more than twice daily was more effective. "Because in vitro data have suggested that the antiadhesion activity of cranberry juice on fimbriated E coli lasts for approximately 8 hours after ingestion, dosing more frequently than twice daily may be a reasonable choice," write the authors.

Caution Needed

"[T]he 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," the authors conclude.

The authors have disclosed no relevant financial relationships.

Arch Intern Med. 2012;172:988-996.

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