Thirteen randomised controlled trials (1,616 participants across nine parallel group and four crossover designs) were included in the review. Six trials had a high risk of bias for at least two out of the five criteria assessed. Many aspects of trial quality were unclear; only four studies had a low risk of bias for three or more of the five criteria assessed. Loss to follow up ranged from 0 to 48%. None of the crossover trials had washout periods.
Ten trials (1,494 participants) that reported cumulative incidence of urinary tract infection were included in the meta-analysis as follows:
After excluding one outlying trial, results showed that cranberry-containing products were effective in preventing urinary tract infections (RR 0.62, 95% CI 0.49 to 0.80; moderate heterogeneity: Ι²=43%). The estimate was robust in sensitivity analysis, although the protective effect of the intervention was greatest in trials without placebo in the control group (RR 0.36, 95% CI 0.21 to 0.62; two trials; no heterogeneity).
Subgroup analyses showed that cranberry-containing products were most effective in women with recurrent urinary tract infection (two trials); females (four trials); children (mean age under 18 years; two trials) those using cranberry juice (five trials); and when products were used more than twice a day (four trials).
The authors stated that there was no evidence of publication bias.