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Am Fam Physician. 2002;65(3):490-494

Up to 60 percent of women have had at least one urinary tract infection (UTI), and about 30 percent have recurrent UTIs. Dietary components that alter the fecal coliform bacteria are reputed to have prophylactic action against UTI but have not been extensively studied. Kontiokari and colleagues studied the effect of cranberry-lingonberry juice and a drink containing Lactobacillus cultures on recurrence of UTI in young Finnish women.

The study authors recruited female students and staff members of a university health center who had a confirmed history of UTI caused by Escherichia coli. Fifty of the 150 women were randomly assigned to receive 50 mL of cranberry-lingonberry juice daily, 50 were given a Lactobacillus GG drink five days per week, and the remaining 50 women acted as controls. Participants were asked to immediately report any symptoms suggestive of UTI, and all were followed with swab samples at three and 12 months after the start of the study. Urine cultures were obtained from all symptomatic patients.

The average age of participants was about 30 years, and the three groups were comparable in all significant variables. Participants reported an average of six previous UTIs (range: 1 to 30). More than 85 percent of women in each group had received an antibiotic within the previous year to treat a UTI. The study was terminated after six months because the manufacturer stopped production of the cranberry-lingonberry juice. During this six-month period, at least one UTI occurred in eight (16 percent) of the women taking cranberry-lingonberry juice, 19 (39 percent) of those taking the Lactobacillus GG drink, and 18 (36 percent) of the women in the control group. The number of patients who had recurrent infections was significantly lower in the cranberry-lingonberry group than in the lactobacillus or control groups (12 compared to 21 and 19). Forty percent of the 98 UTI episodes reported during follow-up occurred in the lactobacillus group, 39 percent in the control group, and 21 percent in the cranberry-lingonberry group. More than 80 percent of infections were caused by E. coli in all groups. No adverse effects of the interventions were reported.

The authors calculate that the cranberry-lingonberry drink was associated with a 20 percent reduction in absolute risk of UTI compared with control participants. No protective effect was found with Lactobacillus cultures. They suggest that daily intake of cranberry juice could have a substantial impact on the more than 11 million women treated every year in the United States for UTI.

editor's note: The data from this study support the use of cranberry juice as a prophylactic against symptomatic UTIs. Throughout the study, the treatment groups did not differ in colonization rates with E. coli, so the effect of the cranberry juice must lie in enhancing body defenses or suppressing symptoms rather than in eliminating bacteria. This and other observations suggest that UTIs are much more complicated than the classic concept of ascending invasion by pathogens. Perhaps a better model might be autoinfection related to some disturbance of a complex commensal system. Why E. coli changes from a commensal to a pathogen remains a mystery. In the meantime, the “old wives' tale” about cranberry juice appears to be true.—a.d.w.

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Copyright © 2002 by the American Academy of Family Physicians.

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