Nocturnal frequency is one of the most bothersome symptoms among lower urinary symptoms. Recently, salt restriction has been a topic for reduction of nocturnal frequency. However, it is not fully understood how much salt restriction affect nocturnal frequency, nocturnal urine volume or nocturnal bladder capacity.  It is also not well-known whether excessive salt intake lead to increased nocturia. Aim of this study is to examine the effect of increasing or decreasing salt intake on nocturnal urine volume, nocturnal frequency and nocturnal bladder capacity in patients with lower urinary symptoms.

This study included forty-four patients with lower urinary symptoms. They had two or more daily salt intake measurement at any time and simultaneously filled in bladder volume chart. Salt intake was estimated by morning urine using Tanaka’s formula. Nocturnal frequency, nocturnal urine volume and nocturnal bladder capacity were obtained by frequency volume chart. The association of salt intake and salt intake change with urine volume, frequency and bladder capacity was evaluated by the day and night. To precisely assess these association, data with a difference of more than 300 mL in daily urine output over two days were excluded. This study was approved by local ethics committee.

Median age of the patients was 77 years (68-89 years). Baseline nocturnal frequency was 2.0 (0-6.5), nocturnal urine volume was 546mL (100-1350 mL), and nocturnal bladder capacity was 200mL (50-437 mL). Median salt intake was 10.5 g/day (6-14.4 g/day)  and baseline salt intake was significantly associated with nocturnal frequency and nocturnal urine volume (p=0.009, p=0.001, respectively). Median change of salt intake was -0.3 g/day (-4.1 to 5.4 g/day). Salt restriction or excessive salt intake was significantly decreased or increased nocturnal urine volume (p=0.004). One-gram salt restriction lead to 36.5mL decrease of nocturnal urine volume. But, salt intake change was not significantly associated with nocturnal frequency nor nocturnal bladder capacity (p=0.29, p=0.91, respectively). Salt restriction was associated with nocturnal urine volume, but not associated with decrease of nocturnal urinary frequency. Effect of salt restriction is limited. Nocturnal frequency should be treated with salt restriction in conjunction with other treatments.

Salt restriction was associated with decreased nocturnal urine volume, but not associated with decrease of nocturnal urinary frequency nor nocturnal bladder capacity. One-gram salt restriction lead to 36.5mL decrease of nocturnal urine volume. Effect of salt restriction for the treatment of nocturnal frequency is limited.

Salt restriction for the treatment of nocturnal frequency should be  in conjunction with other treatments.