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Studies took a new direction in 1984 when researchers at Youngstown State University realised that the cranberry's ability to inhibit bacteria from sticking to the walls of the urinary tract might account for cranberry juice's unique urinary tract health benefits.

Exciting research in the past decade suggests this bacterial anti-adhesion may extend beyond the urinary tract to the stomach and oral cavity. Other new discoveries of antioxidant activity are linking cranberry to cardiovascular health.

Research is ongoing, but the anti-stick and antioxidant power of this humble red berry may prove to provide even more health benefits in the future.

Click here to see the pick of the crop in cranberry research since 1984.

How does it do that? The cranberry, dissected

The summary below explains in detail how cranberry juice can work to maintain the health of the urinary tract. More references can also be found online at the American Website of the Cranberry Institute.

A Proposed Mechanism of Action for Cranberry Juice and Health Maintenance in the Urinary Tract. Current research supports the premise that cranberry juice acts to help maintain urinary tract health by inhibiting adherence of certain bacteria to mucosal and/or epithelial surfaces. Bacterial adherence to mucosal surfaces is generally considered to be an important requirement for colonization and infection. It is believed that compounds found in cranberry act in an anti-adhesive way such that certain bacteria are prevented from adhering and are swept away in the urine.

The mechanistic studies measured the ability of various bacteria to adhere to epithelial cell surfaces using in vitro techniques, and evaluated this activity in both human and animal urine after subjects were given cranberry juice. Cranberry juice interferes with adherence of a surface component of certain E. coli and other Gram-negative bacteria to at least a few types of epithelial cells, including uroepithelial cells [1]. Lowe and Fagelman provide a comprehensive review on mechanistic studies [2].

Bacteria, including E. coli have different types of adhesins on the pili or fimbriae that attach to epithelial cells. It appears that cranberry juice contains a relatively unique component that inhibits certain adhesins (P-fimbriae) of some pathogenic strains of E.coli. Only those juices from the Vaccinium genus tested (cranberry and blueberry) contained the mannose-resistant (P-fimbriated) adhesin inhibitor, whereas other juices tested did not [3]. Preliminary research suggests that this adhesin inhibitor appears to act against a number of types of bacteria, but not all.

In 1998, using in vitro techniques, Howell et al had identified proanthocyanidins (PACs, also known as condensed tannins) as the compounds in cranberries that are responsible for preventing P-fimbriated E. coli from adhering to the urinary tract [4]. Cranberry PACs are polymers of flavan-3-ols, such as catechin and epicatechin, and while monomers and dimers had little anti-adhesion activity, the higher molecular weight trimers and higher oligomers had the greatest activity in vitro [5, 6].

Because those PACs with greatest activity were of higher molecular weight, the question arose as to whether the body could absorb them. In 2001 a study was completed in which extracts of purified cranberry PACs were fed to mice. The urine was found to exhibit anti-adhesion activity against P-fimbriated E. coli, providing the first in vivo evidence that cranberry PACs and/or metabolites can be absorbed into the blood, and into urine, thereby eliciting this anti-adhesion effect [6].

If you would like any further information or updates on the benefits of cranberries, copies of research papers, leaflets or requests for study days, please contact the Cranberry Information Bureau, Field House, 8 High Street, Hurstpierpoint, West Sussex, BN6 9TY or email cib@fml-pr.co.uk.