Equol is produced when daidzein, a soy isoflavone, is metabolized by gut microbiota. It is said that approximately 50% of Japanese women produce equol. Equol is associated with the development of female menopausal symptoms and lifestyle-related diseases that cause overactive bladder (OAB). Our previous study has shown that the age of onset of lower urinary tract symptoms (LUTS), including OAB, is higher in equol producers than in non-producers. On the other hand, while standard treatment agents for OAB are β3 agonists and anticholinergics, there are no reports examining the response to these drugs in relation to equol production. Therefore, the aim of this study was to investigate the relationship between equol production and the efficacy of OAB treatment.

Postmenopausal female patients newly diagnosed with OAB at our institution were included in this study. Patients were divided into two groups based on equol production: producing group (EQ-P) and non-producing group (EQ-N). We retrospectively compared patient characteristics, subjective symptoms, and objective findings before and after treatment. Subjective symptoms were assessed using the OAB Symptom Score (OABSS), with OAB defined as Q3 score (urgency) ≥ 2 and total OABSS ≥ 3. Objective findings were assessed by uroflowmetry and post-void residual. All patients received standard treatment for OAB such as β3 agonists and anticholinergic agents, and outcomes were evaluated after 12 weeks of treatment. The presence or absence of equol production was assessed using spot urine samples, with a cut-off value of 1.0 µmol/L. Patients were also divided into early-onset and late-onset groups based on the median age of onset of LUTS, and similar studies were conducted within each group.

This study included 61 patients: 32 (52.5%) with EQ-P and 29 (47.5%) with EQ-N. The age of onset of LUTS was 67.2 ± 11.0 years for EQ-P and 60.4 ± 10.1 years for EQ-N, which was significantly higher in EQ-P (P=0.038). There were no differences between EQ-P and EQ-N in total OABSS (9.34±2.94 vs 9.41±3.12, P=0.928) or voided volume (219.0±126.7 mL vs 227.3±140.3 mL, P=0.826) before treatment. The changes in total OABSS before and after treatment were -4.13 ± 2.99 for EQ-P and -3.93 ± 3.52 for EQ-N (P=0.817). There were also no significant differences in post-treatment voided volume (226.1±126.9 mL vs 218.8±122.5 mL, P=0.838) or post-void residual (13.8±30.6 mL vs 18.9±36.1 mL, P=0.589) between the two groups. The median age of LUTS onset for patients was 65 [42-83] years, with the early-onset group defined as LUTS onset age of ≤64 years and the late-onset group as ≥65 years. In the early-onset group, EQ-P tended to have a lower OABSS Q3 than EQ-N (3.23±0.83 vs 3.83±1.04, P=0.096). However, there were no significant differences between EQ-P and EQ-N in the changes in total OABSS before and after treatment (-4.23±2.71 vs -4.06±3.39, P=0.879) or in the rate of deviation from OAB due to treatment (69.2% vs 50.0%, P=0.462). In the late-onset group, there were no differences between EQ-P and EQ-N in patient background, OABSS or objective findings, nor in the changes in total OABSS before and after treatment (-4.05±3.24 vs -3.73±3.90, P=0.807), or in objective findings after treatment.

This study confirmed once again that the age of onset of LUTS was significantly higher in equol-producers than in non-producers, but there was no difference in the treatment effect of OAB. These findings indicate that equol production may inhibit the development of LUTS, however, once OAB develops, it does not affect treatment outcomes.

Equol production may help prevent the onset of female LUTS in women with OAB, but it does not influence treatment efficacy once OAB is established.