Cranberry Proanthocyanidins and the Prevention of Urinary Tract Infections: A Meta-Research Analysis of ClinicalTrials.gov Registrations

Background: Cranberry products are widely used to prevent urinary tract infections (UTIs), but clinical evidence remains inconsistent. This registry-based meta-research study characterized the landscape, design, and results reporting of cranberry trials registered on ClinicalTrials.gov, with emphasis on A-type proanthocyanidins (PACs), and descriptively summarized the posted results of completed trials of UTI prevention. Methods: All 200 trials registered under the term “cranberry” (any status or condition) were classified by study type, intervention class, primary outcome theme, and enrollment size. Completed interventional trials assessing cranberry for UTI prevention were then screened for a focused narrative synthesis, with reporting informed by PRISMA 2020; no meta-analysis was performed given clinical heterogeneity. Results: Of 200 registered trials, 52 (26.0%) evaluated cranberry for UTI or bacteriuria; of these, 37 (71.2%) were completed, and 33 of the 37 (89.2%) were interventional. Of the 33 completed interventional trials, 26 (78.8%) had no results posted, and one of the 7 with posted results was excluded because cranberry was part of a combined intervention. Six completed trials met the inclusion criteria: a single post-surgical trial reported fewer clinically diagnosed UTIs with cranberry capsules of unspecified PAC content, whereas a one-year nursing home trial showed no benefit, a long-term care feasibility study posted no efficacy comparison, and a one-month nursing home pilot dose-ranging study reported fewer urine samples with E. coli bacteriuria plus pyuria with cranberry than with placebo, without a consistent dose–response; two juice-based mechanistic/biomarker studies, which did not assess clinical UTI outcomes, showed low urinary PAC-A2 levels. Conclusions: Cranberry trials registered on ClinicalTrials.gov show a large results-reporting gap and inconsistent reporting of PAC content and dosing. The limited posted evidence is insufficient to establish benefit in any setting; the single positive post-surgical trial requires replication in adequately reported trials.