Cranberry is the best-known natural preventive option for frequent UTIs. It first emerged as an effective intervention for bladder and urinary tract health in the early twentieth century. Scientists speculated that the benzoic acid in cranberries was metabolized to hippuric acid and excreted in the urine, which prevented bacterial growth by creating an acidic environment in the bladder.
Since then a wealth of clinical data have detailed the precise mechanism by which certain constituent components of the whole cranberry act to powerfully counter UTI onset.9-12 The most recent studies do not indicate a change in urine pH brought about by cranberries (meaning they do not acidify urine). Instead, cranberry’s antimicrobial action arises from a class of flavonoids called proanthocyanidins (PACs). In addition to exerting potent antioxidant effects, cranberry PACs block bacteria from taking hold of the cells lining the urinary tract.
The surfaces of E. coli and many other bacteria are covered with motile, tendril-like structures called fimbriae. The fimbria acts as a kind of tentacle, enabling bacteria to “grab onto” other microorganisms, inanimate objects and—most importantly—host cells. A single bacterium may possess as many as 1,000 fimbriae. It is this feature that renders E. coli and other species endowed with fimbriae—including Staphylococcus saprophyticus, Salmonella, and Helicobacter pylori—especially virulent and infectious. They employ these structures to latch onto cells in the mucous membranes at multiple sites of the body and initiate a debilitating and potentially lethal proliferation.
A 2009 study demonstrated conclusively that cranberry PACs provoke disabling alterations in the fimbriae and other surface properties of the E. coli bacterium, vastly diminishing its capacity to attach specifically to the surface of the cells lining the urinary tract.9
This process, known as bacteriostasis, prevents harmful bacteria from colonizing the urinary tract. Instead, they are flushed from the urethra during the natural voiding process.