BACKGROUND: The cranberry produces antimicrobial compounds such as proanthocyanidines in response to microbial invasion. In vitro it is able to prevent growth, adhesion or biofilm formation of a large number of bacteria, while clinically, cranberry juice has been shown to prevent urinary tract infections (UTI) in women. However, the effect of cranberry on bacterial colonization more widely has not been evaluated. We were interested in studying cranberry juice in children since many children with recurrent UTI need long-term antimicrobial prophylaxis and would benefit from an alternative.

OBJECTIVE: To evaluate the effect of cranberry juice on nasopharyngeal and colonic bacterial flora, to evaluate how well cranberry juice is accepted by children and to evaluate its effect on infectious diseases and related symptoms.

DESIGN: Children (mean age 4.3 years) in day care centers were randomized to receive either cranberry juice (n=171) or a placebo (n=170) for 3 months. Bacterial samples were collected before and after the intervention and analyzed for both respiratory bacterial pathogens and enteric fatty acid composition, reflecting changes in the colonic bacterial flora. Infectious diseases and their symptoms were monitored using symptom diaries. Compliance was evaluated as the number of drop-outs during the trial and by counting the numbers of doses taken.

RESULTS: The carriage of respiratory bacteria did not change significantly during the intervention, while fecal fatty acid composition changed significantly with time (P0.001) but did not differ between the groups (P>0.05). Cranberry juice had no effect on common infectious diseases or their symptoms. The cranberry juice was well accepted: the number of drop-outs in 3 months was 18 (11%) in the cranberry group and 11 (7%) in the placebo group, and most of the doses were taken as instructed, 145 (88%) and 129 (77%) children, respectively, taking at least 90% of the doses.

CONCLUSIONS: Cranberry juice was well accepted by the children, but led to no change in either the bacterial flora in the nasopharynx or the bacterial fatty acid composition of stools. Thus cranberries seem to have beneficial effect on urinary health only and this is not compromised by other unexpected antimicrobial effects.