Purpose: We investigate the causes of nocturnal urinary frequency and reaso
ns for its increase with age.
Materials and Methods: All voided volumes and times were recorded for 3 day
s in 188 healthy older men without prostatic diseases during a mass screeni
ng program for prostatic diseases in Japan. Nocturnal urinary frequency for
each night was defined as the frequency during sleep not counting the morn
ing 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 b
ladder capacity, and nocturnal and diurnal urinary volume were evaluated.
Results: Multiple regression analysis demonstrated nocturnal bladder capaci
ty and urinary volume to be significant independent determinants of nocturn
al frequency. In age related analysis nocturnal bladder capacity and diurna
l urinary volume decreased with age, while nocturnal urinary volume did not
change.
Conclusions: Nocturnal urinary volume and nocturnal bladder capacity were t
he 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 cha
nge, In older men a decrease in water intake might influence age related ch
anges in urinary volume.