Do cranberries really help prevent urinary tract infections?

Urinary tract infections (UTIs) are the most common urologic disease among women in the U.S., occurring in 102 out of every 100,000^[1] women.You can see how the rate varies with age in Figure 1. While rarely fatal, UTIs cause tremendous discomfort and result in a large financial burden on the healthcare system, at roughly $2.6 billion in annual health care expenses.

Standard treatment for UTIs involves the use of antibiotics, a treatment strategy that substantially increases the risk of antibiotic resistance. Furthermore, fluoroquinolone antibiotics may have serious side effects, such as tendon rupture^[2], leading the FDA to advise that they should not be used for uncomplicated infections, including uncomplicated UTIs. These issues with antibiotics have given researchers reason to look for other methods for preventing UTIs. For decades, the idea has circulated that cranberry juice can treat ^[3]or prevent^[4] UTIs, and some evidence from clinical trials suggests^[5] that this idea is more than a old wives’ tale, although the evidence for UTI prevention is more robust^[6][7] than for treatment.

In addition to clinical evidence, there is some mechanistic data to support the idea that consumption of cranberries might reduce UTIs. Cranberries are rich in a compound called proanthocyanidins. Proanthocyanidins have documented antibacterial properties^[8] against both Gram-positive and Gram-negative bacteria. Furthermore, administration of proanthocyanidin-rich cranberry powder^[9] for six months reduced the risk of UTI by over 50% over 12 months.

Currently, the evidence in the literature regarding the efficacy of cranberry for preventing UTIs is mixed. Two different^[10][11] meta-analyses have shown conflicting findings. The disparate findings are the result of researchers including different studies and having different criteria for analysis. Additionally, the previous meta-analyses examined both complicated and uncomplicated UTIs, the latter of which is more serious and is treated very differently in the clinical setting, compared to the uncomplicated variety. Some factors that would make a UTI complicated are shown in Figure 2. Furthermore, these analyses included both men and women, who have dramatically different rates of UTIs. The present study is a systematic review and meta-analysis that was designed to cut through some of the issues present in the previous meta-analyses and evaluate the evidence concerning cranberry’s ability to prevent uncomplicated UTIs in otherwise healthy women.

UTIs are the most common form of urologic disorders and occur frequently in women. UTIs are often treated with antibiotics, some of which can have serious side effects, and many of which can lead to antibiotic resistance over time. Cranberry, due in large part to its high levels of proanthocyanidins, may be a viable non-antibiotic approach to preventing recurring uncomplicated UTIs among women.