Do Cranberries Help Prevent Urinary Tract Infections?Complementary and Alternative Therapies Evidence-based Summary
Date of review: February 2006
View the plain language summary of this evidence review below.
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Treatment in brief
Cranberry (Vaccinium macrocarpon) to prevent urinary tract infection
Urinary tract infection
Urinary tract infections are caused by bacteria in the urinary tract, usually in the bladder (cystitis). They are very common, especially in women. The most common symptoms of urinary tract infections are a frequent or urgent need to pass urine, or a burning sensation when passing urine. The diagnosis is confirmed by a urine test, which measures the concentration of bacteria (most commonly Escheria coli) in the urine.
Cranberries
Cranberry juice has traditionally been used for preventing urinary tract infections. Its effect may be due to its ‘anti-adhesive’ properties, as it has been demonstrated that cranberries contain compounds that prevent bacteria from sticking to the lining of the bladder (Zafriri 1989). Cranberry can also be taken as a capsule.
The evidence
There is level 1 evidence from a systematic review that taking cranberry products for twelve months reduces the number of urinary tract infections in women who have a problem with recurrent urinary tract infections. When taken over one year, cranberry prevents recurrent infections for about one in six women.
It is not clear whether cranberry products are also effective for other groups who commonly get urinary tract infections, such as older men and children with bladder problems.
Cranberries do not seem to have any serious side effects for most people and there is evidence (level 2) that cranberry juice is generally well accepted and tolerated by older people. Some children find the taste unpleasant.
There is no evidence as to what form of cranberry treatment (eg, juice or tablets) is most effective, what dose is best or for how long it should be taken.
Other important issues
There is evidence suggesting that cranberry products may interfere with the action of the drug warfarin (level 4 evidence). People taking warfarin may wish to limit their intake of cranberries, or carefully monitor their warfarin levels (INR test).
Key messages
| Evidence | Level of evidence |
| There is evidence that cranberry products may reduce the number of recurrent urinary tract infections for women | 1 |
| The evidence suggests that cranberry products may interfere with the action of warfarin | 4 |
| There is no evidence that cranberry products prevent urinary tract infections in children or men | No study evidence |
| There is no evidence for deciding the dose required to reduce infection, or whether juice or capsules are better | No study evidence |
Key: Levels of evidence
| 1 | 2 | 3 | 4 |
| Evidence with a high degree of reliability | Evidence with reliability, but open to debate | Some evidence without a high degree of reliability | Some evidence, but based on studies without comparable groups. |
Reference
The information in this summary was developed by assessing:
Disclaimer: This summary does not provide specific medical advice and the information provided should not be used as a substitute for seeking medical advice from a registered health practitioner.
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