Should cranberry products be recommended for the prevention of urinary tract infections (UTIs)?
Cranberry products are not effective and should not be recommended for the prevention of UTIs. (Strength of Recommendation: B, based on inconsistent or limited-quality patient-oriented evidence.)
Cranberry products have been used for many years to treat and prevent UTIs. Biochemical research suggests that cranberry products might prevent UTIs by altering the levels of hippuric acid in urine, or by preventing bacterial adhesion to the uroepithelial cells in the wall of the bladder. Cranberry products include juice, syrup, capsules, and tablets, but there is no consensus about which form or dose might be the most effective for UTI prevention. A 2008 Cochrane review found two good-quality randomized controlled trials (RCTs) that suggest drinking cranberry juice may decrease the number of symptomatic UTIs over a 12-month period in women,1 and a 2012 meta-analysis added 11 additional RCTs and concluded that cranberry-containing products are associated with a small protective effect against UTIs.2
In this Cochrane review, the authors of the 2008 review sought to update the evidence for the effectiveness of cranberries in the prevention of UTIs in susceptible populations (e.g., women with recurrent UTIs, patients with a neuropathic bladder or spinal injury, older adults) and to incorporate trials of cranberry products for UTI prevention in children. Fourteen additional good-quality trials were added that changed the overall conclusion. Across all populations of patients studied (i.e., women with recurrent UTI, older men and women, adults or children needing catheterization, pregnant women, and children with a susceptibility to UTIs), the use of cranberry products was not associated with a reduced risk of UTIs when compared with placebo (relative risk [RR] = 0.86; 95% confidence interval [CI], 0.71 to 1.04). Two studies of women with recurrent UTIs (RR = 1.31; 95% CI, 0.85 to 2.02) and one study involving children (RR = 0.69; 95% CI, 0.32 to 1.51) failed to demonstrate a difference between cranberry products and antibiotic prophylaxis in reducing the risk of repeat UTIs. Three studies that compared various doses of cranberry products (RR = 1.12; 95% CI, 0.75 to 1.68) and three studies that compared high-dose cranberry products with placebo (RR = 1.02; 95% CI, 0.79 to 1.31) all failed to demonstrate any difference in the rate of UTIs.
Reports of adverse effects and adherence were highly variable. To maintain the level of cranberry intake theorized to be necessary for UTI prevention, a patient would need to consume 150 mL of cranberry juice twice daily, a potentially prohibitive regimen because of cost, taste, or concerns about calories. Guidelines published in 2010 recommended that cranberry products be considered alongside antibiotics as prophylaxis for recurrent infections.3 However, family physicians should counsel their patients that the most current evidence fails to demonstrate sufficient effectiveness of cranberry products in preventing UTIs.