The study supports levels outlined by a French health claim, issued in 2004, for the North American cranberry (Vaccinium macrocarpon​) with at least 36 milligrams of proanthocyanidins (PAC) to “help reduce the adhesion of certain E. coli bacteria to the urinary tract walls”​, and subsequently fight urinary tract infections (UTIs).

Indeed, a lower dose of 18 mg of cranberry PACs was less effective, according to the results of a randomized, double-blind versus placebo study based in Japan, Hungary, Spain and France.

On the other hand, a higher dose of 72 mg was even more efficient at protecting against bacterial adhesion in the urinary tract, according to findings published in the open-access journal BMC Infectious Diseases​.

PACs are also not exclusive to cranberries, but can be found in a range of foods, including green tea, grapes, apples, and chocolate. However, the main type of PACs in cranberry – called A-type PACs - are different from those in these other source – called B-type PACs. Only cranberry PACs may prevent bacterial adhesion.

Led by Amy Howell from the Marucci Center for Blueberry and Cranberry Research and Extension at Rutgers University, the researchers note that, while the urinary tract benefits of cranberry are well documented, it was not known how cranberry PACs may affect the persistence in urine samples over a longer time period. They also sought to determine the "most effective dose per day and to determine if the urinary anti-adhesion effect following cranberry is detected within volunteers of different origins"​.

Howell and her co-workers recruited 32 volunteers from the four countries and randomly assigned them to receive 0, 36 or 72 milligrams of PACs per day in Japan and Hungary, and 0, 18 and 36 milligrams per day in France and Spain. Participants crossed over to all of the interventions with one week washout between stages.

The researchers used the commercially available Urell product supplied by France’s Pharmatoka, and the PACs content was determined using the new DMAC method, state the researchers.

Results showed that a dose-dependent effect. After six hours the 18 mg dose displayed an anti-adhesion activity of 50 per cent, compared with an average of 90 per cent for the 36 mg dose and 100 per cent for the 72 mg dose, said the researchers.

After 24 hours, no anti-adhesion activity was displayed for the lower dose, while the 36 and 72 mg doses had anti-adhesion activities of 12.5 and 50 per cent, respectively.

“These results highlighted for the first time that to achieve a bacterial anti-adhesion effect in urine, 36 mg of cranberry PAC equivalents per day is effective, but 72 mg may offer a [day and night] protection,”​ wrote Howell and her co-workers.

The kinetic data revealed that while there was good activity for both 36 and 72 milligrams after 6 hours, this decreased after 24 hours, “suggesting that it may be beneficial to consume cranberry in two split doses of 36 mg in the morning and evening”,​ they added.

“Further human trials are needed to correlate the level of ex vivo anti-adhesion activity with prevention of clinical UTI,”​ stated the researchers.

Source: BMC Infectious Diseases​

2010, 10​:94, http://www.biomedcentral.com/1471-2334/10/94​

“Dosage effect on uropathogenic Escherichia coli anti-adhesion activity in urine following consumption of cranberry powder standardized for proanthocyanidin content: a multicentric randomized double blind study “​

Authors: A.B. Howell, H. Botto, C. Combescure, A-B. Blanc-Potard, L.Gausa, T. Matsumoto, P. Tenke, A. Sotto, J-P. Lavigne