Urinary Tract Conditions: Examining the Evidence on Cranberry

From the Spring 2010 issue of Quality Care®, NAFC's newsletter


From the National Center for Complementary and Alternative Medicine (NCCAM)

Patients with urinary tract infections (UTI) often ask healthcare providers about using complementary and alternative medicine (CAM) to relieve symptoms or prevent recurrences. There are many reasons that CAM therapies may appeal to these patients--for example, if they are concerned about the side effects or costs of prescription medicines, worried about antibiotic resistance, or seeking "natural" approaches to treating these conditions.

UTIs occur at all ages and in both genders, although the incidence is 50 times higher in adult women as compared to adult men. Up to one-third of women have at least one recurrence after their first episode. In adult men, UTIs are uncommon before age 50 and often are caused by an uderlying disorder, such as kidney stones or an enlarged prostate. UTIs in older adults may be caused by a condition such as post-menopausal vaginal atrophy in females or incomplete emptying of the bladder.

UTIs are the second most common bacterial infection after respiratory infections. E. coli is most often the cause, but other mocroorganisms may also play a role.

Cranberry
The natural product that is most used for UTI, and on which there is the most evidence, is cranberry (Vaccinium macrocarpon). In a 2007 national survey on Americans' use of CAM, among those who used natural products, about 1.6 million people used cranberry.

The mechanism of action of cranberry is not fully understood, but basic research has yielded findings that may explain its potential benefit in UTIs, such as the suggestions that:

  • Proanthocyanidins (molecules that help create intense color in fruits and vegetables and are thought to have antioxidant properties) unique to cranberry inhibit the ability of bacteria to adhere to the surface membrane of host cells in the urinary tract.
  • Cranberry has anti-inflammatory and antioxidant activity.

Practice Guidelines
The American College of Obstetricians and Gynecologists (ACOG) released an evidence-based clinical practice guideline in 2008 on sudden or severe bacterial infection of the bladder or lower urinary tract in nonpregnant women. Among ACOG's recommendations are to use antibiotics as first-line therapy. ACOG notes that drinking cranberry juice has been shown to decrease recurrence of symptomatic UTIs, although the optimal length of treatment and concentration of juice still needs to be determined.

Systematic Reviews/Meta-Analyses
Two systematic reviews/meta-analyses on cranberry from the Cochrane Collaboration concluded the following:

  • A 2008 review on cranberry to prevent recurrent UTIs (updated from 2004) included 10 randomized or quasi-randomized clinical trials. Most (seven) studied cranberry in the form of juice, and four studied tablets (1,049 participants in total). The review found "some evidence" that cranberry juice may decrease the number of syptomatic UTIs over a 12-month period comared with placebo/control, especially in women with recurrent UTIs. Applicability to other groups was less certain. The review noted uncertainty as to what the optimum dosage or form is for cranberry therapy.
  • A 2009 review on cranberry to treat UTIs concluded that there is no good-quality evidence on this question.

Research on cranberry for urinary tract conditions is ongoing, including in National Center for Complementary and Alternative Medicine (NCCAM) supported studies using well standardized, research-grade cranberry products.

Safety
Cranberry appears to be generally well tolerated in appropriate food amonts. High doses can cause gastrointestinal symptoms. Some commercial products are high in calories and sugar. There is indication that long-term use in high amounts might be contraindicated in persons at risk for uric-acid kidney stones. Safety data on long-term use are needed. General cautions that apply to the use of dietary supplements apply here. For more side effect and safety information, click here.

About the author:

The National Center for Complementary and Alternative Medicine (NCCAM) is the federal government's lead agency for scientific research on complementary and alternative medicine (CAM). NCCAM sponsors and conducts research using scientific methods and advanced technologies to study CAM.

The mission of NCCAM is to explore complementary and alternative healing practices in the context of rigorous science, train compementary and alternative medicine researchers, and disseminate authoritative information to the public and professionals.