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Cranberries & UTI’s: Another Old Wives’ Tale?

By: Mallory Gilliam

March 4, 2009 years, mothers have sworn by cranberry juice as a cure for urinary tract infections. However, only in the past few decades has this old wives’ tale been put under some scientific scrutiny by the medical community. Before, manufacturers of cranberry juice and other cranberry products were frustrated by their inability to capitalize on the already widely held pro-health beliefs associated with cranberries. But now, a multitude of health studies (often funded by such manufactures) have been  conducted and have been able to add some scientific basis to the claims. In result, the cranberry product market has exploded, with every company boasting the wide range of health benefits that cranberries possess, including those for urinary problems. So could it be that Mom was right? Do cranberries actually cure urinary tract infections?


The Background


Urinary Tract Infections

Image of the human form showing location of kidneys, ureters, bladder, and urethra. Urinary tract infections, commonly referred to as UTI’s, refer to an infection of any structure which urine passes through leaving the body, including the kidneys, ureters, bladder, or urethra. The most common location and point source of these infections is the urethra, which is the tube that runs from the bladder to the exit point of the body. The least common, but most serious, location of infection is in the kidneys, which serve to eliminate waste and water from the blood by producing and expelling urine. The farther up along the urinary tract the infection spreads, from urethra to kidney (see illustration 1), the more serious it is considered.






The Facts

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Urinary tract infections are the second most common type of infection that occurs in the human body and account for 8.3 million of the doctor appointments each year. It has also been found that UTI’s occur significantly more frequently in women than men, with 40% of women developing one in their lifetime, as opposed to 12% of men. The infections are also less common in children, as only 1 – 2% become infected, but are considered more serious if indeed developed.  (


The Symptoms

When examining the symptoms of a urinary tract infection, the two degrees of infection must be considered. The first being cystitis, or lower urinary tract infection, which affects the urethra and bladder and is the least severe of the two. The most common symptom reported is pain, or “burning” sensation, during and after urination, known as dysuria. A person might also experience an increased frequency and sense of urgency in urination, or even hesitancy, which refers to the sensation that one has to urinate, but cannot, or at least not completely. In some cases, sufferers may also experience bloody urine. The more serious infection of the upper urinary tract, including the ureters and kidneys, is known as pyelonephritis and is associated with more severe symptoms, such as a high fever, nausea, and vomiting (


The Causes urinary tract is designed to expel fluid, salts, and waste products from the body, and usually the urine produced is sterile. However, an infection will occur when bacteria, most commonly Escherichia coli (E. coli) from the colon, is present in the urine and clings to the end point of the urethra and begins to multiply. The longer the infection goes without treatment, the more the bacteria proliferates and eventually spreads up the rest of the urinary tract causing the more serious stage of infection. The spread of E. Coli in these cases is most often associated with poor hygiene and sexual intercourse. Two other microorganisms, Chlamydia and Mycoplasm, may also cause a urinary tract infection, but these are closely related to sexually transmitted diseases, and can only be affective through sexual intercourse. There are certain groups of people at risk and/or pre-disposed to UTI’s including those with diabetes, kidney stones, immune deficiencies, women who are postmenopausal or using a diaphragm as a method of birth control, or men with an enlarged prostrate  ( Pregnant women are also at a higher risk for the infection to spread to the kidneys, once developed. Recurrences are another trend found in women with UTI’s, with 20% of women developing a second infection, then 30% of those women will develop a third, and then a staggering 80% of women who develop a third infection developing yet a fourth (


The Cranberry: Not Just a Thanksgiving Staple as theVaccinium macrocarpon, the American cranberry, or the bog cranberry, this fruit has been considered a health cure-all, be it for diabetes, diarrhea, stomach and liver problems, or urinary infections, for years. Native to North America, this small red fruit has been used in since the tribal days of the continent both as food and in ceremonies, as well as for medicinal purposes. The first commercial field was planted in Massachusetts in 1816, and today there are well over 40,000 acres in the US and Canada dedicated to their production. This berry is readily available in a variety of forms, including dried, in sauce and juice, as well as fresh from about September to December (





The Claims

If a search for the word “cranberry” is conducted on the web, a handful of links to health sites will be pulled up., a web database geared towards health consumers, clearly demonstrates cranberries’ grip on the health community. Their page provides additional links to articles on the “powers” of the cranberry in promoting wellness and specifically for preventing urinary tract infections. The website also displays advertisements for the “top cranberry products” ranging from capsules to powders ( One such advertisement, for’s cranberry tablets markets the product as a way to reap the same health benefits as provided by cranberry juice cocktail while consuming a fraction of the calories. While the major motive behind this claim is of course to sell the product, the website also adds basis to the claim by adding that,

                “Studies in the New England Journal of Medicine & Journal of American Medical Association suggest that cranberry works to promote and maintain a healthy urinary system”

( Manufacturers of already popular cranberry products, like cranberry cocktail, are also using the scientific findings to promote their brands. Take the household name, Ocean Spray. Their company’s webpage features a whole health tab with general information and also breaks down cranberries’ health benefits specifically for several body parts, from the mouth to bones. Needless to say, it contains a page on cranberries’ effect on the urinary tract. According to Ocean Spray,

“Research shows drinking Cranberry Juice Cocktail daily can promote urinary tract health. The benefits of Cranberry Juice Cocktail start within two hours and can last up to ten hours. That means one serving (8 oz.) of Cranberry Juice Cocktail in the morning and one at night may better help keep certain harmful bacteria at bay all day. Bye, bye bacteria. Hello healthy urinary tract.”

All of these websites encourage the incorporation of cranberries into one’s daily diet in one way or another (preferably through their particular product). Their claims are not totally unfounded, as each example makes references to conducted studies. However, it is important to note that the only claim being made by cranberry product manufacturers in reference to urinary health is that the consumption of cranberries can prevent urinary tract infections, not cure them.


The Theory reasoning cited behind cranberry’s ability to prevent urinary tract infections lies behind the compounds of proanthocyanidins, also known as condensed tannins or PAC’s, found in cranberries. These compounds interact with bacteria at a molecular level and actually prevent E. Coli from adhering to the body’s cells, which is what causes the infection in the first place. The PAC’s cause the microscopic hairs, or fimbrae, of the E. Coli, which allow the bacteria to attach itself to the lining of the urinary tract, to constrict, and therefore preventing the bacteria from ever doing so. 



The Science

The claims being made that cranberries can prevent urinary tracts because they contain proanthocyanidins are a direct reflection of the scientific studies that have been conducted. There are a multitude of review articles that support the same conclusion, and several that build onto the same thesis with a little more detail.

Testing the Anit-Adherence Properties of Proanthocyanidins

Agniel et. Al (2006) conducted a study examining the in vitro bacterial anti-adherence properties of cranberry juice in samples’ urine in comparison to a placebo, which exactly what PAC’s are supposed to be responsible for.

   -The Design:  randomized, double blind, cross-over, placebo-controlled study

   -Sample: 10 men, 10 women

   -Method: At dinner, each subject received a 750ml dose of liquid comprised of one of the following:

     750ml placebo, 250ml placebo/500ml mineral water,  250ml cranberry juice/500ml mineral water,

     or 750ml cranberry juice 

     Each subject received each formula in turn, in a random order, with at least a 6 day flush period in between each one. Urine samples were collected the morning after administration. Six strains of bacteria from UTI patients were extracted and grown in the urine samples in order to test the adherence of the bacteria to bladder cells, or T24 cells.

  -Results: The tests resulted in the lowest adhesion index being associated with the pure cranberry  

formula (750ml), the next lowest being the diluted cranberry formula (250ml cranberry/500ml water).

The diluted placebo formula and the 750ml placebo formula showed little to no effect on the reduction adherence to the cells.   


How Proanthocyanidins Prevent E. Coli Adhesion

The study conducted by Liu et. Al (2008) examined the effect cranberry juice had on the molecular adhesion of E. coli bacteria to uroepithelial (bladder) cells by measuring and comparing the contact angle, interfacial tensions and Gibs free energies of adhesion of E. coli bacteria to the cell walls in control samples as well as samples treated with cranberry solution.

     -Method: The strains of E. coli bacteria were suspended in an aqueous solution of either 0, 5, 10, or

      27% cranberry juice and incubated

    -Results: E. coli had a strong tendency to adhere to the uroepithelial cells with an average of

     50.2 ± 22.9 present per each cell. The samples treated with cranberry solution showed a significant

    reduction in adhesion rate with an average of 13.6 ± 5.7, 9.3 ± 4.1, and 2.9 ± 1.5 for the 5, 10, and 27%

    cranberry solutions, respectively.

These results had a direct correlation with the decrease in angle of adhesion the bacteria were able to attain, proving therefore that PAC’s cause E. coli bacteria to compress which, in turn, causes their fimbrae to malfunction.


Other Useful Information Revealed – Cranberries vs. Resistant E. coli Strains

Howe et. Al (2002) conducted a study which went further to prove that cranberry juice is effective in reducing the adhesion capabilities of E. coli strains that are resistant to antibiotic treatment used for UTI’s.

     -Method: Thirty-nine E. coli isolates were collected from women ages 18 – 39 with diagnosed UTI’s.

       The isolates were then incubated in urine taken from healthy women both before and after the

       consumption of cranberry juice cocktail and proanthocyanidins concentrate. The isolates chosen to

       be tested were a subset of those proven to be resistant to antibiotics. After incubation, the bacteria

       was harvested and screened for their ability to adhere to uroepithelial cells.


    -Results: Urine after consumption of cranberry juice cocktail prevented the adhesion of 31 out of

     39 (80%) of the isolates and 19 out of 24 (79%) of the antibiotic-resistant isolates. The pre cranberry

     juice consumption urine failed to prevent any of the isolates from adhering to the cell walls. The

    samples tested in the proanthocyanidins concentrate prevented all of the isolates from attaching.


This demonstrates that PAC’s found in commercial cranberry juice are just as effective in preventing the adhesion of simple E. coli strands as anti-biotic resistant strands. Furthermore, it shows that the use of a higher concentrate of proanthocyanidins is completely effective in preventing E. coli adhesion. This information is very valuable as it suggests the use of cranberry products in preventing UTI’s might be more strategic as it would not encourage further development of resistant E. coli strands as traditional antibiotics do.  

The Conclusion & Recommendations first did prove that the consumption of cranberry juice, in as little dosage as 750ml, results in a 62% reduction in bacterial adherence to the cells found in one’s urinary tract (Agniel 2006). Therefore the claims found on websites, such as Ocean Spray’s, that cite the “anti-stick” property of PAC’s are rooted in scientific truth. The second study affirms this conclusion by examining the exact effect PAC’s have on the process E. coli undergoes to attach itself to bladder cell walls. It has also been proved that the proanthocyanidins in cranberries are effective in treating E. coli strains which have developed a tolerance for the antibiotics used to treat urinary tract infections traditionally. However, it once again needs to be reiterated all of the studies conducted to date only prove that cranberries are effective in preventing UTI’s, not in treating them. Future studies are necessary in order to test that particular hypothesis, in which even more variables must be taken in account. If a urinary tract infection is suspected, seeking medical care is still recommended. The traditional treatment of a UTI still typically consists of some type of oral anti-biotic, like amoxicillin ( On the other hand, if a patient suffers from recurring or chronic UTI’s, which is not uncommon, incorporating cranberry juice into their daily routine, would prove extremely beneficial in preventing future infections.















Literature Cited

Di Martino, P., R. Agniel, et al. (2006). "Reduction of Escherichia coli adherence to uroepithelial bladder cells after consumption of cranberry juice: a double-blind randomized placebo-controlled cross-over trial." World Journal of Urology 24(1): 21-27.

Howell, A. B. and B. Foxman (2002). "Cranberry Juice and Adhesion of Antibiotic-Resistant Uropathogens." JAMA 287(23): 3082-3083.

Liu, Y., A. M. Gallardo-Moreno, et al. (2008). "Cranberry changes the physicochemical surface properties of E. coli and adhesion with uroepithelial cells." Colloids and Surfaces B: Biointerfaces 65(1): 35-42.







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