Cranberry and the Maintenance of Urinary Tract Health

Amy B. Howell, Ph.D., Rutgers University

Consumption of cranberry juice has long been associated with maintenance of urinary tract health, and clinical evidence supports this role.  The majority of urinary tract infections are caused by E. coli bacteria adhering to the walls of the urinary tract and multiplying to cause infection.  For years, it was falsely assumed that the acidity of cranberry juice prevented the bacteria from growing.  In 1998, our group at Rutgers University utilized bioassay-directed fractionation to isolate a specific group of compounds from cranberry fruit called proanthocyanidins (condensed tannins).  We found that these compounds prevented both antibiotic resistant and susceptible uropathogenic P-fimbriated E. coli bacteria from attaching to uroepithelial cells, thus preventing them from multiplying and causing infection.  The bacterial anti-adhesion effect persisted in human urine for up to 10 hours following ingestion of 240 mL of cranberry juice cocktail.  We determined that the cranberry proanthocyanidins have unusual A-type double linkages in their structures, compared to the B-type single linkages in proanthocyanidins found in other foods such as chocolate and grapes (which do not elicit an in vivo bacterial anti-adhesion effect).  The inhibition of bacterial adhesion by the A-type proanthocyanidins and their metabolites could be a potential mechanism explaining cranberry’s effect on prevention of urinary tract infections. 

There have been many studies on the health benefits of consuming cranberry juice and cranberry products, especially in relation to maintenance of urinary tract health.  The US National Institute of Health (NIH) recently reviewed these studies and determined that there was support for cranberry’s role in preventing urinary tract infections; however several clinical study results were questioned due to certain design flaws and participant compliance issues.  In response to these questions, NCCAM (The National Center for Complimentary and Alternative Medicine), a branch of NIH, recently funded research proposals aimed at resolving the questions raised by previous research on cranberry and urinary tract infections and to support cranberry research in other promising areas.  The scope of funded projects includes clinical intervention trials on cranberry as a UTI preventative, studies relating to cranberry’s mechanism of action and interaction with certain drugs, and one project on the use of cranberry to maintain oral cavity health. Several of these studies will be reviewed in this presentation. 

Key words:  Cranberries, urinary tract infection, E. coli, bacteria, proanthocyanidin, A-type linkage, tannin, anti-adhesion