Cranberry juice has been used as a ‘folk remedy’ for treating UTI and some observational and small randomised trials had suggested a clinical basis for its effects.
But researchers at the University of Michigan School of Public Health found women who drank the juice for six months showed no improvement in incidence of a second UTI compared with a placebo drink.
In the study, 319 women with acute UTI were randomised to drink either 27% cranberry juice or a placebo drink twice a day for six months.
The overall recurrence rate was 16.9% across both groups. Recurrence was actually slightly higher in the active cranberry drink group at 20%, but this difference was not statistically significant.
Researchers had expected 30% recurrence rates, in line with established literature.
The lower overall incidence of UTI may have meant the placebo inadvertently the ingredient in cranberry juice that may reduce UTI recurrence. Or, the study design may have meant participants were kept hydrated and caused them to urinate more regularly, they said.
The study authors concluded: ‘Contrary to expectation, we found that drinking an 8oz [240-ml] dosage of cranberry juice twice per day gave no protection against the risk of recurring UTI among college-aged women.’