Researchers in Australia recently published the results of their 6-month randomized, placebo-controlled, and double-blinded clinical trial in The American Journal of Clinical Nutrition, reporting on the efficacy of supplementing with whole cranberry fruit powder for women with recurrent urinary tract infections (UTIs). 150 women with a history of recurrent UTIs, defined as ≥ 3 UTIs in the last year or ≥ 2 UTIs in the last 6 months (but excluding women with > 5 within 6 months), received one daily capsule of either placebo or 500 mg whole cranberry powder. Urine cultures were performed at baseline, 3 months, 6 months, and any time a woman presented with symptoms of a UTI.
At 6 months, the whole cranberry extract reduced culture-confirmed UTIs by 52% compared to placebo. Additionally, E. coli was the most frequently detected uropathogenic species in UTIs, and its incidence was also reduced by 51% among women taking cranberry extract. UTIs with symptoms of frequency and urgency were reduced by 71%, with a 59% reduction in the mean total number of UTIs per participant. There was no difference between groups regarding safety outcomes, with no serious adverse events reported.
This finding is roughly consistent with most trials and meta-analyses evaluating some form of cranberry for UTI prevention. For example, a systematic review and meta-analysis published in the Journal of Nutrition, which included seven randomized and controlled trials, found a 26% lower risk of UTI among healthy women at higher risk. The reduction in E. coli incidence noted in this recent study is plausibly cranberry’s mechanism of action, as cranberry has been demonstrated to have an anti-adhesive effect in the bladder. This may be particularly important given a study that found that nearly all women with UTI symptoms have E. coli detectable by PCR (polymerase chain reaction), even when cultures are negative.