Does ingestion of cranberry juice reduce symptomatic urinary tract infections in older people in hospital? A double-blind, placebo-controlled trial

Background: cranberry juice is often given to older people in hospital to prevent urinary tract infection (UTI), although there is little evidence to support its use.

Objective: to assess whether cranberry juice ingestion is effective in reducing UTIs in older people in hospital.

Design: randomised, placebo-controlled, double-blind trial.

Setting: Medicine for the Elderly assessment and rehabilitation hospital wards.

Subjects: 376 older patients in hospital.

Methods: participants were randomised to daily ingestion of 300 ml of cranberry juice or matching placebo beverage. The primary outcome was time to onset of first UTI. Secondary outcomes were adherence to beverage drinking, courses of antibiotics prescribed, and organisms responsible for UTIs.

Results: a total of 21/376 (5.6%) participants developed a symptomatic UTI: 14/189 in the placebo group and 7/187 in the cranberry juice group. These between-group differences were not significant, relative risk (RR) 0.51 [95% CI 0.21–1.22, P=0.122). Although there were significantly fewer infections with Escherichia coli in the cranberry group (13 versus 4) RR 0.31 [95% CI 0.10–0.94, P=0.027], this should be interpreted with caution as it was a secondary outcome.

Conclusion: despite having the largest sample size of any clinical trial yet to have examined the effect of cranberry juice ingestion, the actual infection rate observed was lower than anticipated, making the study underpowered. This study has confirmed the acceptability of cranberry juice to older people. Larger trials are now required to determine whether it is effective in reducing UTIs in older hospital patients.