Elucidating Characteristics of Co‐Existent Overactive and Underactive Bladder in Participants of the 2023 Japan Community Health Survey (JaCS 2023) With Nocturia

OBJECTIVES: To clarify the characteristics of co-existent overactive and underactive bladder (COUB) in participants with nocturia from the 2023 Japan Community Health Survey. SUBJECTS AND METHODS: Participants reporting nocturia (≥1 episode per night) were divided into four groups: COUB, overactive bladder (OAB) alone, underactive bladder (UAB) alone, and neither OAB nor UAB (non-OAB/UAB). Nocturia-related variables were compared across groups. Multivariable analyses were performed to identify predictors of clinical nocturia (nocturia ≥ 2) and factors associated with reporting nocturia as the most impactful symptom in daily life. RESULTS: Among 2,006 men and 1,787 women with nocturia, the prevalence of COUB was 6.1% and 2.6%, respectively. The proportion of nocturia ≥2 increased significantly in ascending order across four groups in men (non-OAB/UAB, UAB alone, OAB alone, COUB) and women (non-OAB/UAB, OAB alone, UAB alone, COUB) (p < 0.001 for both). Subjective nighttime voided volume (VV) compared to daytime VV and nocturnal voiding trigger also showed significant differences among the four groups in both genders (all p < 0.001). COUB independently predicted nocturia ≥ 2 in men (odds ratio OR: 2.50, p < 0.001) and women (OR: 2.39, p = 0.028). Although nocturia was ranked as the most impactful symptom in all groups, COUB was inversely associated with reporting nocturia as the most impactful symptom (men: OR: 0.43, p = 0.014; women: OR: 0.18, p = 0.002). CONCLUSION: COUB represents a distinct and severe phenotype among symptom syndromes and is independently associated with nocturia severity.