Causes of nocturnal urinary frequency and reasons for its increase with age in healthy older men

PURPOSE: We investigate the causes of nocturnal urinary frequency and reasons for its increase with age. MATERIALS AND METHODS: All voided volumes and times were recorded for 3 days in 188 healthy older men without prostatic diseases during a mass screening program for prostatic diseases in Japan. Nocturnal urinary frequency for each night was defined as the frequency during sleep not counting the morning void. Relationships between nocturnal urinary frequency and functional bladder capacity, nocturnal bladder capacity, nocturnal urinary volume and sleep time were analyzed. Age related changes in functional and nocturnal bladder capacity, and nocturnal and diurnal urinary volume were evaluated. RESULTS: Multiple regression analysis demonstrated nocturnal bladder capacity and urinary volume to be significant independent determinants of nocturnal frequency. In age related analysis nocturnal bladder capacity and diurnal urinary volume decreased with age, while nocturnal urinary volume did not change. CONCLUSIONS: Nocturnal urinary volume and nocturnal bladder capacity were the significant determinants of nocturnal urinary frequency in healthy older men. The increase of nocturnal frequency with age was thought to be due to a decrease in nocturnal bladder capacity, since urinary volume did not change. In older men a decrease in water intake might influence age related changes in urinary volume.