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Fact or Fiction: Do Cranberries Prevent Urinary Tract Infections?

Morgan B. Chatman

September 24, 2007

Introduction: The Popular Belief

The popular belief that cranberry juice is capable of preventing urinary tract infections is prevalent within the minds of thousands of individuals.  The debate as to whether cranberries are indeed effective in preventing urinary tract infections is still ongoing, yet several individuals (particularly researchers) have taken distinct positions on the issue. 

The most widely believed theory is that cranberries, in any form (i.e., juice), contain specific ingredients that are capable of preventing the bacteria responsible for urinary tract infections from attaching to the wall of the bladder.  Some research studies have yielded results that validate this particular belief.  However, a significant number of other studies have produced inconclusive results. 

Within this literature review, the effect of the purposeful ingestion of cranberries on urinary tract infections will be analyzed in hopes of finding either supporting or refuting evidence.  A brief description of urinary tract infections and the chemical composition of cranberries will be discussed initially. Then, a description and analysis of a small, yet prominent portion of the existing research studies examining the effects of cranberries on urinary tract infections will be provided in attempts to finally settle this long-standing debate.

Background: Urinary Track Infections

            Urinary tract infections are a persistent health problem for a great deal of individuals, specifically women, within this country.  Approximately 11 million women a year report having had a urinary tract infection (Howell, 2007).  Additionally, statistically speaking, research has indicated that one out of five women, at some point within their life, will experience a urinary tract infection (Ross, 2006).  Increased urinary frequency, urgency, and painful urination are but a few indicative symptoms of urinary tract infections (Ross, 2006).  The primary cause of urinary tract infections is the notorious microorganism Escherichia coli (otherwise know as E. coli) which attaches to the cell membrane of the epithelial cells that line the urinary tract (Ross, 2006). 

Antibiotic therapy is the most standard treatment for urinary tract infections (Howell, 2007).  However, increased bacterial resistance to the frequently proscribed antibiotics has influenced some physicians to seek alternative treatments or remedies as a means to deal with the problem (Howell, 2007).  Also, many women have been noted to turn to natural therapies (i.e., the cranberry) as a means to address, primarily prevent, this prevailing issue (Ross, 2006).


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Background: The Cranberry

            One of the only three fruits indigenous to North America, the cranberry (Vaccinium macrocarpon) has persistently been esteemed for its natural medical and nutritional properties (Ross, 2006).  Historically speaking, the cranberry’s documented therapeutic qualities have included treatment of bladder and kidney problems, relief of blood disorders, stomach ailments, vomiting, appetite loss, scurvy, and even cancer (Lynch, 2004).  In addition, the cranberry, for nearly 100 years, has been a used as an alternative, popular treatment for urinary tract infections (Howell, 2007).

            Cranberries are composed mostly of water (approximately 80%) and carbohydrates (approximately 10%) (Raz, Chazan, & Dan, 2004).  Flavonoids, anthocyanins, catechin, triterpenoids, organic acids, and ascorbic acid are the other existing constituents that make up remaining 10 percent.  Cranberries are typically processed into fresh fruit, concentrate, sauce products, and juice drinks because of the acidity (pH, < 2.5) of its single-strength juice (Raz et al, 2004).  Quinic acid, malic acid, and critic acids are the most common acids found in cranberries that contribute to their natural acidity. The two compounds within the cranberry that have been long thought to inhibit the adherence of bacteria to the lining the of bladder wall include fructose and a polymeric compound of an unknown nature (Jepson, Mihaljevic, & Craig, 2004).

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Existing Research Studies

“Clinical Applications of Cranberry in Urinary Tract Infections” (Stephanie Ross)

            Ross states that the historical claim asserting that cranberries are useful as a remedy for problems affecting the urinary tract has been validated through current scientific research.  This “current research, [according to Ross], indicates that drinking cranberry juice in therapeutic amounts, on a regular basis, appears to reduce the risk of [urinary tract infections], and may help in the treatment of existing [urinary tract infections]” (Ross, 2006).  In order to prevent the occurrence of urinary tract infections and treat existing urinary tract infections, Ross proclaims that 4 to 32 fluid ounces and 16 to 32 fluid ounces of cranberry juice or approximately 18 fluid ounces of unsweetened cranberry juice (respectively) should be consumed daily (Ross, 2006).

            The effectiveness of cranberry juice, according to Ross, lies in its ability to prevent bacteria from attaching to the walls of the urinary tract. Proanthocyandins are the primary constituents within cranberries that Ross believes are ultimately responsible for their anti-adhesion effect.  However, Ross admits that cranberries are not a substitute for antibiotics in the treatment of recurrent and acute urinary tract infections that can possibly lead to serious, more complicated kidney infections (Ross, 2006).

            Lastly, Ross explains the possible adverse effects of the therapeutic dosage levels and drug interactions.  Besides diarrhea or mild gastrointestinal upset from consuming more than 3 to 4 liters of cranberry juice daily, there are not any known adverse effects of the therapeutic dosage levels (Ross, 2006).  In addition, there are not any known adverse drug interactions with antibiotics or any other prescription drugs and the consumption of cranberry juice.


“Cranberry for Prevention of Urinary Tract Infections” (Darren Lynch)

            Just as Ross, Lynch proclaims that the primary mechanism of cranberries, relating to urinary tract infections, is its ability to inhibit the adhesion of various bacteria (primarily E. coli) to the bladder’s wall.  Lynch explains the findings of studies that were conducted to determine the effectiveness of the cranberry.  Some of the studies produced inconclusive results.  However, two of the studies’ results indicated that the consumption of cranberry juice or cranberry extract tablets on a regular basis significantly decreased the subject’s number of urinary tract infection symptoms within the year over which the experimentation was conducted (Lynch, 2006).   There were a total of 150 participants that were randomly placed into either a control or treatment group within both of these studies (Lynch, 2006).

            Each of the studies that were reviewed by Lynch documented different doses and formulations of the cranberry.  Some of the studies suggested the consumption of unsweetened cranberry juice while others recommended the consumption of a cranberry juice cocktail or extract tablets.  Nonetheless, the most recent study reviewed in Lynch’s report suggested that either consuming a cranberry extract (300 to 400 mg) twice daily or 8 fluid ounces of unsweetened cranberry juice three times daily was necessary to produce results (Lynch, 2006).

“Bioactive Compounds in Cranberries and Their Role in Prevention of Urinary Tract Infections” (Amy Howell)

            Through a tedious evaluation of other existing research studies examining the effects of some form of the cranberry on urinary tract health, Howell’s research proposes that 8 to 10 fluid ounces of sweetened (either with sugar or artificial sweetener) cranberry juice or cranberry juice cocktail has shown to significantly reduce the incidence of urinary tract infections by approximately 50 percent (Howell, 2007).  Howell’s research also suggests that because the cranberry compounds are not capable of actually destroying the bacteria, the cranberries, thus, are much less likely to produce resistant strains of bacteria as opposed to antibiotics (Howell, 2007).  In addition, Howell states that there is currently new data that may suggest that cranberries are not only capable of preventing urinary tract infections but treating existing ones as well.  Those facts, however, are inconclusive at this time.

“Cranberry Juice and Urinary Tract Infection” (R. Raz, B. Chazen, and M. Dan)

            The Raz, et al. review highlights the limitations of many of the existing studies examining the effects of cranberries on urinary tract infections.  Most of the clinical trials that have been conducted, according to Raz et al., have utilized several formulations of cranberry products including cranberry juice concentrate, cranberry juice cocktail, cranberry capsules, etc. which have contributed to the limitations of the studies because of the lack of consistency.  Raz et al. does not make any suggestions about the effect of the cranberry, but instead they simply note that more research yet needs to be conducted in order for there to be conclusive results (Raz et al., 2004). 

“Cranberries for preventing urinary tract infections (Review)” Cochrane Collaboration

            The main objective of the Cochrane review was to asses the overall effectiveness of cranberry juice on preventing urinary tract infections.  All published randomized controlled trials examining cranberry juice and/or products and urinary tract health in susceptible populations (i.e., women) were reviewed (Jepson et al., 2004). Once all of the necessary data (methods, participants, interventions, etc.) from each of the studies was collected, statistical analysis was conducted for the purpose of identifying whether there were any statistically significant results (Jepson et al., 2004).

            The main results of the Cochrane review were that the comprehensive body of evidence is simply not clear.  Some studies yielded positive results while others provided inconclusive results.  Through their review, it was ultimately concluded that “further properly designed trials with relevant outcomes are needed” in order to successfully determine whether cranberries are capable of preventing urinary tract infections (Jepson et al., 2004).

Conclusion: Are Cranberries Capable of Preventing Urinary Track Infections? 

According to most of the existing research studies, the results as to whether cranberries are actually effective in preventing urinary tract infections are inconclusive.  Some researchers agree that the consumption of cranberry juice or some equivalent form (i.e., cranberry extract tablets) will lead to a significant decrease in the incidence of urinary tract infections.  However, there appears to be a lack of research in order to appropriately support this assumption.  Nonetheless, most researchers do at least agree that cranberries do possess natural compounds that could possibly assist with urinary tract infections, but they are still unsure about the form and the dosage of the cranberries (i.e., sweetened or unsweetened, cocktail or extract; 8 fluid ounces or 16 fluid ounces) that must be consumed in order to yield the most positive results.  With that said, until enough research has been conducted to produce conclusive results, the consumption of cranberries is NOT yet proven to prevent urinary tract infections.






Howell, A. (2007). Bioactive compounds in cranberries and their role in prevention of urinary     

tract infections. Mol. Nutr. Food Research, 51, 732-737.

Jepson R. G., Mihaljevic, L., Craig, J. (2004). Cranberries for preventing urinary track

infections. Cochrane Database of Systematic Review, CD001321.

Lynch, D. M. (2004). Cranberry for prevention of urinary tract infections. American Family

Physician, 70(11), 2175-2177.

Raz, R., Chazan, B., Dan, M. (2004). Cranberry juice and urinary tract infection. Clinical

Infectious Diseases, 38, 1413-1419.

Ross, S. (2006). Clinical applications of cranberry in urinary tract infections. Holistic Nursing

Practice, 213-214.








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