Cranberry products prevent UTIs - research finds

Wednesday 11th June 2008 9:17am

From Harvard Medical School

In what may be the biggest boost for cranberries since Thanksgiving, researchers with the highly respected Cochrane Collaboration — experts who identify and evaluate studies of health care interventions — say that scientific evidence supports daily consumption of cranberry products to reduce the likelihood of urinary tract infections (UTIs). The preventive effect is strongest in women with a history of recurrent UTIs — that is, three or more a year.

Cranberry juice has been used for years to treat and prevent UTIs, which are roughly 50 times more common in women than in men. UTIs can affect any part of the urinary tract but occur most often in the bladder (cystitis), producing symptoms of frequent, urgent, or painful urination, and sometimes abdominal pain or blood in the urine. Most UTIs are caused by Escherichia coli, or E. coli, which can travel from the anus to the urethra during activities such as using the toilet or having sexual intercourse. Women are more vulnerable to UTIs than men are, because a woman’s urethra is close to the vagina and anus, allowing bacteria easier access to the bladder. Antibiotics are very effective in preventing and treating these infections, but side effects deter many women from taking them.

The research

The Cochrane reviewers searched medical databases and clinical trial registries and consulted cranberry industry sources to find studies that lasted at least one month and compared cranberry juice, capsules, or tablets with a placebo or water for the prevention of UTIs in a variety of populations. They identified 10 studies — involving a total of 1,049 participants — that met their inclusion criteria. Results showed that over a 12-month period, cranberry products reduced the overall incidence of UTIs by 35%. Among women with recurrent symptomatic UTIs, cranberries cut the annual rate of new infections by 39%.

One of the drawbacks of the studies being reviewed was their lack of consistency in dosing and in the concentration of cranberries. Also, the chemical composition of the cranberry products was not standardized, and it is unclear whether the juice, capsules, and tablets all carry the same effect. So it’s hard to know exactly which and how much of the various cranberry components people were getting, or what level of intake was effective. (The traditional recommendation is a glass or two of 100% cranberry juice a day.)

How do cranberries help?

Cranberries contain several compounds that could confer health benefits, including salicylic acid (the active ingredient in aspirin) and plant chemicals called polyphenols, which have antioxidant properties. No exact mechanism of action has been established, but in laboratory tests, cranberry extracts have been shown to hamper the ability of E. coli to stick to the type of cells that line the urinary tract.

A possible limitation of cranberry therapy is that regular cranberry juice is fairly high in calories (130 to 140 calories per 8 ounces, about 50% more than orange juice and even colas). Also, the flavor may not be agreeable to some people, especially over the long term. Fortunately, there are many other things you can do to help stave off UTIs:

If you continue to have problems, talk to your clinician about prophylactic antibiotic therapy — that is, taking an antibiotic daily, or after intercourse, or for a few days at the first sign of symptoms.

Source: Harvard Medical School [] © 2000–2008 Harvard University. All rights reserved.

For more information on urinary conditions, order our Special Health Report, Better Bladder and Bowel Control, at www.health.harvard.edu/BBBC.