Equol is a metabolite of the soya isoflavone daidzein that can be produced via the formation of the intermediate dihydrodaidzein by human intestinal bacteria. It resembles natural estrogens with an affinity to estrogen receptors. In humans, not everyone can produce equol from gut metabolism and approximately 30–40% of the adult population has the ability to perform this transformation. It is postulated that equol producers benefit more than non-equol producers for all the endocrine-related effects.　Since postmenopausal estrogen deficiency causes atrophic changes in the lower urinary tract and may be associated with lower urinary tract symptoms (LUTS), we evaluated the association between equol-producing status and LUTS in Japanese women.

44 Japanese women with LUTS who visited our hospital (group L) and 63 Japanese women without LUTS who volunteered to participate (group C) were recruited and examined for equol-producing status using urine sample. The diagnosis of LUTS was determined by OABSS（Overactive Bladder Symptom Score）, ICIQ-SF (International Consultation on Incontinence Questionnaire-Short Form) and IPSS( International Prostate Symptom Score). “Without LUTS” was defined as not meeting diagnostic criteria for overactive bladder by OABSS, and ICIQ-SF total score of 3 or less, and IPSS total score of 7 or less.　The concentration of equol in urine was measured by high-performance liquid chromatography. All the measurements in group L were conducted before the treatment for the patients’ conditions. Equol producers were classified as individuals having a level of equol in urine>1µM.

Mean ages of the two groups were group L; 56.9 (8.7) vs group C; 55.2 (5.9) years old (SD), respectively. The diagnosed condition of women in group L were overactive bladder (n=17), stress urinary incontinence (n=18), mixed urinary incontinence (n=9), interstitial cystitis/bladder pain syndrome (n=7) and pelvic organ prolapse (n=13). Total scores of each questionnaire in group L were OABSS; 4 [0-12], ICIQ-SF; 8.5 [0-19] and IPSS; 9.5 [3-25] (median [min-max]), respectively. The number of women capable of producing equol in group L was significantly lower than that in group C : group L;12 (27.3 %) vs group C; 29 (46.0 %), p = 0.0495.

Although there are many reports suggesting an association between low female hormone levels and LUTS, no studies have examined the relationship between equol-producing status and LUTS. In the present study, the number of equol-producers in the LUTS group was significantly lower than that in the control group, suggesting that there may be some association between female lower urinary tract symptoms and the ability to produce equol.

Small sample size and various conditions in LUTS group limited power to detect the specific association of equol with female LUTS. However, since the present study clearly showed that there were more equol producers in the group without LUTS than in the group with LUTS, the impact of dietary phytoestrogens and their metabolites on female LUTS should be explored more.