Equol is produced when daidzein, a soy isoflavone, is metabolized by intestinal bacteria. Approximately 50% of Japanese women produce equol. Equol has an estrogenic effect, and similar to estrogen, has been linked to lifestyle-related diseases, such as hypertension, diabetes, dyslipidemia, and menopausal disorders. In addition, genitourinary syndrome of menopause (GSM), which results in lower urinary tract symptoms (LUTS) due to urogenital atrophy owing to the decreased secretion of sex hormones during menopause, has attracted attention in clinical settings. Estrogen therapy for GSM has been reported to reduce urogenital atrophy and improve LUTS. Estrogen therapy has also been considered for the treatment of pelvic organ prolapse (POP), which is thought to be caused by reduced estrogen secretion; however, its therapeutic efficacy for POP treatment remains controversial. Thus far, there have been no reports on the association between estrogenic equol and POP. Therefore, the aim of this study is to clarify the association between the presence or absence of equol production and the occurrence of POP and its associated LUTS including overactive bladder (OAB).

Female patients who received a diagnosis of POP at our hospital between April 2019 and December 2023 were included in our study. Patients were divided into two groups according to the presence or absence of equol production. Differences in patient background, such as age at onset, subjective symptoms of OAB, and other objective findings, such as POP-Q score and uroflowmetry (UFM), were examined retrospectively. We evaluated the subjective symptoms using the Overactive Bladder Symptom Questionnaire (OABSS); a urinary urgency score (Question 3) of at least 2 points and a total OABSS score of at least 3 points was defined as OAB. UFM was used to assess voided volume, maximum flow rate (Qmax), and post-void residual urine (PVR). We also evaluated equol production in spot urine samples and determined equol levels using an enzyme-linked immunosorbent assay. The cutoff value of urinary equol for its production was defined as 1.0 µmol/L.

We included 56 eligible patients in the present study; 32 (57.1%) in the equol-producing group and 24 (42.9%) in the non-producing group. The age at onset of POP was 70.6 ± 6.8 years in the equol-producing group and 66.1 ± 5.0 years in the non-producing group, with the non-producing group exhibiting a significantly younger age at onset (P=0.0083). The body mass index (BMI) at the time of diagnosis of POP was 23.2±3.5 kg/m2 in the equol-producing group and 25.1±3.1 kg/m2 in the non-producing group, with the non-producing group exhibiting a significantly higher BMI (P=0.0368). In terms of other patient characteristics, such as the number of surgical histories, such as total hysterectomies and cesarean sections, number of vaginal deliveries, and history of OAB treatment, we did not find any significant differences between the two groups. In terms of subjective symptoms, the OABSS indicated no difference between the two groups in terms of the daytime frequency (Q1), urinary urgency (Q3), and urgency incontinence (Q4); nonetheless, nocturia (Q2) was significantly higher in the producing group than in the non-producing group (2.27±0.80 vs 1.27±1.03, P=0.0103). Objective findings also suggested that the POP-Q score (2.84 ± 0.64 vs 2.83 ± 0.56, P=0.9564), voided volume (241.9 ± 132.8 mL vs 279.4 ± 147.3 mL, P=0.4229), Qmax (21.0 ±11.1 m/s vs 22.2±14.9 m/s, P=0.8834), and PVR (52.1±94.2 mL vs 95.1±118.8 mL, P=0.2012) did not differ between the two groups.

In this study, we found that the equol-producing group had a significantly higher age at onset of POP and a significantly lower BMI at the time of diagnosis than the non-producing group. These findings indicate that equol exposure may play an important role in suppressing the onset of POP. However, we speculate that the presence or absence of equol production had little effect on the differences between the subjective and objective findings at the time of diagnosis of POP. Equol has estrogen-like effects and is thought to maintain the health of female urinary and reproductive systems, protect vascular function, and reduce oxidative stress. These pharmacological effects suggest that equol may play a role in reducing the onset of POP, even indirectly, by reducing blood flow disturbances in the pelvic floor muscles and maintaining connective tissue.

Equol may delay the onset of POP.