Cranberry Supplement Tied to Greater OAB Score Reductions in Pilot Trial

A standardized cranberry supplement was associated with a greater percentage reduction in overactive bladder (OAB) symptom scores than placebo over 4 weeks in 25 women, according to a pilot randomized trial in Frontiers in Cellular and Infection Microbiology.¹ The authors noted that pharmacologic options for OAB are limited by poor persistence, with about 20% of patients continuing treatment at 12 months, largely because of adverse effects such as dry mouth and constipation. Polyphenol-rich cranberry products, which contain proanthocyanidins, have drawn interest as a possible alternative.

Cranberry Group Had Greater Symptom Score Reductions

Investigators at Kansai Medical University in Japan screened female students with an online Overactive Bladder Symptom Score (OABSS) survey. Of 37 respondents who scored 3 or higher, 26 enrolled. Participants (median age, 23 years) received either a daily cranberry supplement containing 36 mg of proanthocyanidins or placebo for 4 weeks. The trial was registered in the UMIN Clinical Trials Registry (UMIN000057544), and the primary end points were the OABSS reduction rate and changes in the urinary microbiome (urobiome).

In the per-protocol analysis of 25 women (12 cranberry, 13 placebo; one placebo participant was excluded for antibiotic use), the median OABSS reduction rate was 66.7% (IQR, 41.7%-70.0%) with cranberry vs 40.0% (IQR, 0%-50.0%) with placebo (P = .039; CI for the difference, 1.3%-44.0%). Median OABSS fell from 3.5 to 1.5 in the cranberry group and from 4.0 to 3.0 in the placebo group. The between-group difference in absolute OABSS change did not reach significance (P = .14). No serious adverse events occurred, and no participants dropped out because of supplement-related adverse effects.

Lactobacillus Shift Did Not Differ Between Groups

Lactobacillus dominated the baseline urobiome, with a median relative abundance of 64.2%. Its relative abundance decreased within the cranberry group (median change, –4.39 percentage points; P = .027; q = .096, under the authors' exploratory cutoff of 0.1) but not within the placebo group. However, the between-group difference in that change was not significant (P = .50), and the change did not correlate with symptom improvement (Spearman r_s = –0.029; P = .93). Because only 31% of Lactobacillus reads could be assigned to species, the authors could not confirm whether the shift reflected a reduction in Lactobacillus iners, which accounted for 99% of the assigned reads at baseline.

The authors said a previous study conducted the only prior randomized trial of cranberry for OAB that they knew of. That trial randomized 98 women to 500 mg of dried cranberry powder or placebo for 24 weeks.² Per-protocol analysis of 60 women showed greater reductions in daily micturitions and urgency episodes with cranberry, but an intent-to-treat analysis showed no significant difference between groups. Participants in that trial averaged about 48 years, vs a median of 23 here, the authors noted.¹

Small Pilot Design Limits Conclusions

The trial was underpowered, with 25 women analyzed against a target of at least 21 per group. It was conducted at a single center on university students with mild baseline symptoms (median OABSS, 3.5 in the cranberry group and 4.0 in the placebo group), and analyses were per-protocol only. The authors also noted that menstrual cycle timing and sexual intercourse were not fully controlled and that midstream urine samples and the absence of negative and blank controls for DNA extraction and polymerase chain reaction mean contamination cannot be excluded. The investigators characterized both the clinical and urobiome findings as "hypothesis-generating rather than confirmatory" and called for larger, multicenter trials with higher-resolution metagenomic or metabolomic analyses.

Marukai Corporation supplied the cranberry supplement and placebo at no cost, and Kobata Research Institute manufactured the supplement. The authors declared no commercial or financial relationships that could be construed as a conflict of interest. Funding included a Japan Society for the Promotion of Science grant.

References

1. Ito A, Akagawa S, Akagawa Y, et al. Efficacy of a standardized cranberry supplement on overactive bladder symptoms and urobiome alterations in young women: a randomized, double-blind, placebo-controlled pilot trial. Front Cell Infect Microbiol. 2026;16:1952206. doi:10.3389/fcimb.2026.1952206
2. Cho A, Eidelberg A, Butler DJ, et al. Efficacy of daily intake of dried cranberry 500 mg in women with overactive bladder: a randomized, double-blind, placebo controlled study. J Urol. 2021;205(2):507-513. doi:10.1097/JU.0000000000001384