To date, although there have been many epidemiological studies on stress urinary incontinence (SUI) in females, only few epidemiological studies on SUI have been conducted in males. Thus, although there might be sex differences in the prevalence of SUI, they have not been clarified to date.
    Female SUI is induced by sphincter deficiency, decreased elasticity of the urethral wall, weakening of the sealing effect of urethral mucosa, etc. Conversely, the causes and associated factors involved in male SUI are reportedly benign prostatic obstruction surgery, neurogenic conditions, pelvic surgery, radical prostatectomy, etc. Thus, the pathophysiology of male SUI is suggested to involve sphincter deficiency. Since there might be sex differences in the pathophysiology of SUI, it is possible that the factors associated with SUI might differ between the two sexes. However, the sex differences regarding the factors related to SUI have not yet been clarified, especially in the same cohort. 
    In 2003, the Japanese Continence Society conducted an epidemiological survey regarding lower urinary tract symptoms (LUTS) in Japan. Twenty years after that previous epidemiological survey, another web-based cross-sectional study was conducted, named the JaCS 2023 (Japan Community health Survey in 2023) study, to survey the prevalence and characteristics of LUTS in Japan.
    The aim of the present epidemiological study was to evaluate the sex-related prevalence of SUI and its associated factors using data acquired from the JaCS 2023 study.

We investigated 3097 males and 3056 females aged 20-99 years. All participants answered web-based questionnaires on their health status and lower urinary tract symptoms. Data on frequency of SUI, comorbidities and health-related behavior were extracted. The Cochran-Armitage trend test was used to evaluate the trend between prevalence of SUI and age. Multivariate analysis was performed using logistic regression analysis to identify factors associated with SUI.

SUI was consistently observed in about 10% of individuals in their twenties and thirties, including in males. There were no age-related differences in the prevalence of SUI in males (P=0.55) (Figure 1). In females, the prevalence of SUI statistically significantly increased with age (P<0.0001) (Figure 2). The frequency of SUI was, however, low in both sexes. Age (OR,1.36; 95% CI, 1.13-1.62), BMI (OR, 1.87; 95% CI, 1.50-2.32) and history of vaginal delivery (OR, 2.15; 95% CI, 1.77-2.63) were only associated with SUI in females. Drinking habit (OR, 1.43; 95% CI, 1.10-1.87) and frequent spicy foods intake(OR, 1.55; 95% CI, 1.19-2.01) were associated with SUI only in males.

In the present study, the prevalence and factors associated with SUI were evaluated in more than 6000 participants through a web-based survey. One of the strongest points of our JaCS study 2023 was that the surveys were conducted in participants aged >20 y. Surprisingly, male SUI was observed even in the younger generation, i.e., among those in their twenties and thirties. In the present study, the prevalence of male SUI was about 10%. 
    In the present survey, while the prevalence of female SUI increased significantly with age, male SUI did not show a significant age-related change in prevalence. Yet, the frequency of SUI was not very high in either sex. Additionally, the prevalence of mild SUI in males (Grade 1 and 2) decreased from the age of twenties to fifties in the present study.
    In the present study, the factors related to SUI were investigated from the perspective of participants’ characteristics and health-related behaviors. Age and BMI correlated significantly with only female SUI, which was consistent with previous reports. Increase in BMI might induce an increase in abdominal pressure, and aging might be associated with weakening of the pelvic floor muscles, both of which would contribute to the increase in female SUI.
    Regarding the association between health-related behaviors and SUI, drinking habit and frequent spice consumption were significantly associated with only male SUI. A previous study demonstrated a significant association between female UI and alcohol intake. Consumption of large amounts of alcohol was associated with a significant increase in the number of participants with male SUI in the present study (data not shown). Thus, intoxication due to alcohol consumption might be involved in male SUI. 
    To the best of our knowledge, this is the first report to demonstrate the association between male SUI and frequent spice consumption. Although the reason for this significant association is unclear, since high intake of chili was previously shown to be significantly positively associated with cognitive decline, some cognitive decline might have triggered male SUI in this study. Since alcohol consumption and frequent spicy food intake are controllable factors, these factors are adjustable factors for SUI.

In this nationwide web-based survey in Japan, the frequency of SUI was low in both sexes. However, the trend between the prevalence of SUI and age was different between both sexes. The prevalence of male SUI was consistently about 10% through all age groups, while that of female SUI increased with age. Especially in males, mild SUI improved with age until the fifties. Female SUI might involve weakness of the pelvic floor muscles, while male SUI might be associated with health-related behaviors.

Continence 12S (2024) 101420
DOI: 10.1016/j.cont.2024.101420