Does ingesting cranberry reduce the frequency of symptomatic urinary tract infections or asymptomatic bacteriuria?
Over a 12-month period, cranberry products decrease the incidence of symptomatic urinary tract infections (UTIs), especially in women with recurrent UTIs. Optimal dosage and form of administration (juice, tablets, or capsules) is unclear. There are no studies comparing cranberry juice with antibiotic prophylactic therapy. Unacceptable taste and gastrointestinal upset are commonly reported adverse effects.
Cranberries are thought to contain a substance that can reduce the incidence of UTIs by changing the surface properties of Escherichia coli. This prevents it from adhering to the wall of the bladder. In this Cochrane review, the authors found 10 studies (N = 1,049; five cross-over and five parallel group) of cranberry products, including juice, concentrate, or tablets. A meta-analysis of four of these 10 studies found that cranberry products significantly reduced the incidence of UTIs at 12 months (relative risk [RR] = 0.66; 95% confidence interval [CI], 0.47 to 0.92) compared with placebo or control.
A meta-analysis of two randomized controlled trials (RCTs) of cranberry products was done for persons with recurrent UTIs (i.e., four or more UTIs in the past year, one or more in the previous three months, or two symptomatic culture-confirmed UTIs in the past calendar year). The study patients were given cranberry concentrate daily in the form of 400 mg capsules, tablets in 1:30 concentrated juice twice per day, or 250 mL of juice three times per day. The meta-analysis showed an RR of 0.61 (95% CI, 0.40 to 0.91) for one symptomatic recurrent UTI. Two studies in older men and women showed no statistically significant difference in symptomatic UTIs in the cranberry group compared with the control group. In those patients requiring indwelling or intermittent catheterization, four studies showed no statistically significant difference in symptomatic UTIs.
One study of older adults using cranberry versus control showed that the persons in the cranberry group were 58 percent (P = .004) less likely to have asymptomatic bacteriuria with pyuria. Five studies of patients needing catheterization showed no statistically significant difference in asymptomatic bacteriuria in those taking cranberry products compared with the control group. Of note, there is no known benefit of treatment of asymptomatic bacteriuria in these populations.
In these studies, drop out rates were generally high (20 to 55 percent). Compliance dropped below 80 percent in many studies of those with recurrent UTIs. Side effects were common and included gastroesophageal reflux, nausea, and frequent bowel movements. Withdrawal rate was high in many studies; some withdrawals were for unknown reasons, whereas other studies cited side effects of gastrointestinal upset, unpleasant taste, cost, caloric load, or high blood sugar.
No national practice guidelines have recommended cranberry juice as a preventive strategy for recurrent UTI. The Society of Obstetricians and Gynaecologists of Canada recommends that women experiencing recurrent UTIs should be instructed that the consumption of pure cranberry-lingonberry juice, rather than cranberry drink, will decrease their risk of urinary infections.1
Cranberry tablets cost $10 to $15 for a 30-day supply; juice costs vary depending on preparation and brand. Based on one recent RCT, a reasonable recommended cranberry tablet dosage is 1 tablet (300 to 400 mg) twice daily; the recommended dosage for unsweetened juice is 8 oz three times daily.2 Caution should be taken in the long-term use of cranberry in patients who are known urinary oxalate stone formers. Cranberry does not have significant drug interactions.2