Treatment for overactive bladder (OAB) mainly requires involves pharmacotherapy such as anticholinergics and β3 stimulants, but drug-resistant patients are often encountered. Pharmacotherapy also raises concerns regarding adverse events including dysuria, dry mouth, constipation, and blood pressure fluctuations; therefore, a safer treatment option is needed, particularly for older patients. 
Chronic excessive salt intake is closely connected with lifestyle diseases such as hypertension and diabetes, which have a profound effect on the onset of OAB. However, there are no studies on the effect of salt intake reduction on OAB symptoms, despite salt intake being a typical factor for improving lifestyle diseases. The aim of this study was to investigate the therapeutic effect of salt intake reduction on subjects with OAB.

Subjects included those with OAB who were also diagnosed with excessive salt intake (men: ≥8 g/day, women: ≥7 g/day). OAB was defined as an overactive bladder symptom score (OABSS) Q3 (urgency) of ≥2 points and a total score of ≥3 points. Nutritional guidance on salt intake reduction was conducted every four weeks using a pamphlet. We conducted a prospective study using the OABSS and frequency volume chart (FVC) to evaluate lower urinary tract symptoms at the start of salt intake reduction and 12 weeks later. Subjects with apparent functional or organic diseases that would induce lower urinary tract dysfunction were excluded. Subjects already taking medication to treat lower urinary tract symptoms were instructed to maintain the content of their pharmaceutical administration throughout the study period. Estimated salt intake was measured based on urine sodium and urine creatinine in spot urine samples. Subsequently, we used a conversion formula corrected for height, weight, and age. P<0.05 was determined to be statistically significant.

There were 98 subjects (men n=52) who could be analyzed; they had a mean age of 66.7±11.5 years. There were 71 subjects (72.4%) who successfully reduced their salt intake during the observation period [success (S) group], and 27 patients (27.6%) who failed to reduce their salt intake [failure (F) group]. The mean estimated salt intake decreased from 10.4±2.2 g to 7.7±2.0 g in the S group (p<0.001) and increased from 9.6±0.9 g to 11.5±1.9 g in the F group (p<0.001).
In the S group, not only did OABSS Q1 (diurnal frequency) improve from 1.2±1.0 to 0.6±1.0 (p<0.001) and Q2 (nocturia) improve from 2.1±0.5 to 1.4±0.7 (p<0.001), but also did Q3 (urgency) improve from 2.3±0.5 to 2.0±0.7 (p<0.001) and Q4 (urgency incontinence) improve from 1.3±1.0 to 1.1±1.0 (p=0.003); the total score improved from 6.9±1.0 to 5.1±2.2 (p<0.001). During the 12-week study period, 17 patients (23.9%) in the S group no longer met the definition of OAB. In the F group, no statistical improvements were seen in any of the OABSS items. There were no patients in the F group who no longer met the diagnostic criteria of OAB.
The voided volume in the S group in the FVC improved from 247.8±25.1 mL to 260.4±32.6 mL (p< 0.001). The number of nocturia in the S group improved from 2.5±1.0 times to 1.6±0.9 times (p<0.001), and the nocturnal polyuria index also significantly improved from 30.7±7.6% to 28.6±7.2% (p=0.007). No improvements were seen in any items obtained in the FVC in the F group.

In this clinical study targeting subjects with OAB who also have excessive salt intake, OAB symptoms improved in the S group, and the number of nocturia and the nocturnal polyuria index significantly declined. There were a certain number of subjects who no longer met the diagnostic criteria of OAB by reducing their salt intake.

We considered that it would be appropriate to consider salt intake reduction as a therapeutic option as part of the lifestyle guidance provided to subjects with OAB and excessive salt intake. It is also preferable to consider salt intake reduction in subjects who have excessive salt intake when treatment for OAB, including pharmacotherapy, is ineffective, or if OAB symptoms are mild.