Age and Nocturnal Polyuria in Nocturia: A Multicenter Voiding Diary Cohort Study

INTRODUCTION: Although the prevalence of nocturnal polyuria (NP) increases with age, the mechanisms underlying age-related changes in voiding patterns and the daytime-nighttime distribution of urine volume remain unclear. Given that the severity of nocturia and bladder function may differ across age groups, age-specific voiding profiles require clarification to enable the development of appropriate management strategies. Therefore, in this multicenter cohort study, we aimed to analyze the urinary patterns and clinical factors associated with NP using a voiding diary. MATERIALS AND METHODS: This multicenter retrospective observational study included patients who presented at 17 Japanese institutions with nocturia as the primary complaint in 2018-2022. The enrolled patients documented at least 2 days of voiding diaries, and their daily voiding patterns were thoroughly analyzed. NP was defined as an NP index (NPi) exceeding 0.33 calculated from 24-h and nocturnal urine volumes. Patients were stratified into five age groups (<50, 50-59, 60-69, 70-79, and ≥80 years) for comparative analysis. The primary study endpoint was identifying the clinical factors associated with NP. RESULTS: A total of 875 patients were included in the analysis. NPi levels increased with age and were significantly higher in the ≥80 years group than that in the other groups (p < 0.05). The prevalence of NP increased with age. A review of voiding diaries revealed that patients aged ≥80 years had significantly lower 24-h and daytime urine volumes and a notably higher incidence of NP than the other age groups (p < 0.05). The patients diagnosed with NP were older and had a higher prevalence of overactive bladder (OAB) than those without NP. A multivariate analysis identified age, the presence of OAB, maximal urinary volume, and 24-h urine volume as independent predictors of NP. CONCLUSIONS: These findings suggest that nocturia in older adults is not exclusively attributable to impaired bladder function. This hypothesis suggests that the condition is multifactorial and involves urinary symptoms, such as OAB, changes in urine volume, and symptoms related to comorbidities.