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Cranberry is a fruit of an evergreen shrub growing in northern parts of North America and Europe, as well as Chile.  The North American cranberry is a native plant with larger fruit and milder flavor than its European relative. Native North Americans gathered wild cranberries and used them for food and medicine, and their juice to dye rugs and blankets. 

In traditional medicine, cranberry juice has been used to prevent (not cure!) urinary tract infections (UTIs).  It was once thought that the antibacterial properties of cranberries were due to their high acid content (second only to lemon and lime) that acidifies urine making it an unsuitable environment for the growth of bacteria. However, a number of laboratory studies have shown that 

Cranberries for UTI prevention

the antimicrobial effect of the cranberry juice is in fact largely attributable to a particular type of molecules: the A-type proanthocyanidins (PACs) that prevent attachment of bacteria (such as Escherichia coli) to the cells lining the urinary tract.


Clinical trials did not provide consistent findings of the effectiveness of cranberry juice in preventing UTI. Two reports, published in 2012 only couple of months apart, analyzed data collected from a number of clinical studies and came to conflicting conclusions. While one study found cranberry juice to be effective in preventing UTIs in women prone to recurrent infections,  the other study reported negligible benefit in all of the tested subgroups.   Both studies, however, noted high patient drop-out rates, most likely caused by the unsustainability of drinking large amounts of cranberry juice over lengthy periods of time. 


Cranberry capsules or tablets are more suitable for prolonged use than is the juice. Most clinical trials that evaluated the efficacy of capsules in preventing UTIs, did not determine the actual amount of active ingredients, PACs, contained in them. Consequently, the findings of these trials could not be used to draw any definitive conclusions. Determining amounts of active ingredients contained in the capsules is especially important because it is suspected that the encapsulation process itself leads to the loss of active ingredients. The only study that did determine and report the amount of PACs in the capsules, found cranberry to be beneficial as a preventive therapy.   Interestingly, even without measuring the active ingredients contained in the capsules, cranberry was still found to be as effective as antibiotics in preventing UTIs in women with recurrent infections.   Considering the growing problem of antibiotic resistance, it seems prudent to invest in further, more carefully designed clinical trials that will conclusively establish the effectiveness of cranberry-based prevention therapies. 


How To Use


Despite indications that cranberry juice might be beneficial, 3WC do not recommend its use for prevention of UTIs. This is due to issues associated with frequent and prolonged consumption of the juice, such as high sugar/calorie intake and its costliness. 

Cranberry supplements for UTI prevention

Where cranberry capsules or tablets are concerned, 3WC only recommend the use of those for which the amount of active ingredients has been accurately determined. A clinical trial that used cranberry capsules with the standardized content of active PACs, found 36mg of PACs per day to be the lowest dose needed to diminish the ability of bacteria, such as Escherichia coli, to cause infection. The same study found that taking two cranberry pills (each containing 36 mg of PACs) a day, one in the morning and one in the evening might offer 24-hour infection protection. 


To potentiate the antibacterial effect of cranberries, make sure you stay well hydrated.  If your health allows, drink 8 glasses of water or some other suitable liquid per day. Frequent urination is essential for removing the bacteria from the urinary tract. 



Cranberry and cranberry products have been in use for many years and are generally regarded as safe. Side effects reported in clinical trials were few and mild (gastrointestinal discomfort, for example).


Cranberries have high levels of salicylic acid, an active form of aspirin. Avoid cranberries and cranberry products if you are allergic to aspirin.


Cranberries also contain high levels of oxalates, which may pose a risk of kidney stone formation (calcium oxalate is the major component of most kidney stones). However, the highest quality cranberry capsules contain only a small fraction of oxalates present in the fruit. If you are prone to kidney stones or are otherwise sensitive to oxalates, make sure you check the oxalate content in the cranberry product you intend to use.


Cranberry Supplementation


We were able to identify only one high quality product that contains 36 mg of active PACs. 


  • Ellura 36 mg PACs

Last updated: August 24, 2016

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