There exists a robust association between nocturia and a variety of cardiovascular diseases. Excessive dietary sodium intake is associated with cardiovascular disease and is an independent risk factor for nocturia in patients seeking urological care, but it remains unclear whether dietary sodium restriction is an effective therapy for nocturnal voiding symptoms beyond urological practice. Notably, there exists a robust association between nocturia and a variety of cardiovascular diseases, including hypertension and congestive heart failure [1]. Moreover, sodium restriction is a first-line intervention in lowering blood pressure in hypertensive patients, and consistently endorsed by heart failure guidelines for improving symptoms in congestive heart failure [2]. 

Accordingly, we sought to determine the effects of sodium restriction on nocturia frequency in a group of patients seen in a real-world inner-city cardiology practice. The primary aim of this study is to test the hypothesis that reduction in dietary sodium intake in accordance with best practice standards for the management of cardiovascular disease results in a significant decrease in average nocturnal voids. A secondary objective is to determine whether there exists an association between patient blood pressure and nocturia frequency.

Study Design and Procedures

Patients who were referred to an outpatient cardiology clinic from 2015-2018 were subject to a comprehensive sodium intake interview and dietary counseling by their cardiologist in accordance with best practice standards in the management of cardiovascular disease. 

A patient-centered approach to sodium restriction was employed, wherein patients were counseled individually by their cardiologist, who identified specific sources of high dietary sodium and provided patients with an individualized treatment plan for dietary sodium restriction as warranted. Comprehensive dietary assessment and counseling were repeated by the same practitioner at routine follow-up.

Average self-reported nocturnal voiding frequency was recorded in the patient’s medical record at each visit. Nocturia was defined as waking to pass urine during the main sleep period, in accordance with current International Continence Society (ICS) terminology [3]. Change in voiding frequency (Δ void frequency) was determined as the voiding frequency at a visit minus the voiding frequency reported at the initial visit. For follow-up visits, the physician determined whether patients had been “strongly adherent,” “somewhat adherent,” or “nonadherent” to dietary modification, which was also recorded in the patient’s medical record.

Retrospective analysis was performed upon approval from the institutional review board. All patient data were obtained from patient chart review and no additional research instruments were needed. A waiver of informed consent was granted for retrospective analysis.

Patient Population

Baseline nocturnal voiding frequency was obtained from 94 total patients, of which 72 (76.6%) were female, and 88 (93.6%) self-identified as black/African-American. These patients 94 had a baseline mean (± sd) age of 66 ± 13 years; Body Mass Index of 33 ± 8 kg/m2; ejection fraction of 57 ± 13 percent, systolic blood pressure of 138 ± 18 mmHg; and diastolic blood pressure of 77 ± 12 mmHg. Hypertension was present in 80 (85.1%) patients; congestive heart failure in 38 (40.4%) patients; diabetes mellitus in 38 (40.4%); hyperlipidemia in 36 (38.3%) patients; coronary artery disease in 20 (21.2%) patients; chronic obstructive pulmonary disease in 14 (14.9%) patients; chronic kidney disease in 8 (8.5%) patients; atrial fibrillation in 6 (6.4%) patients; and aortic stenosis in 5 (5.3%) patients. In total, 29 (30.9%) patients were taking loop diuretics, and 18 (19.1%) were taking thiazide diuretics. 
Of the 94 patients with baseline visits, first follow-up data were available from 76 patients, and second follow-up data were available from 53 patients. The mean (± sd) duration from initial visit to first follow up was 90 ± 117 days, and from second to third 110 ± 141 days. Amongst all first and second follow-up visits, 67.3% were categorized as adherent with sodium restriction, and 32.7% were nonadherent (either did not change or increased sodium intake). 

Statistical Analysis

Pearson correlation analysis was used to determine univariate correlates of Δ void frequency. Multivariate linear regression was used to determine factors independently associated with Δ void frequency.

For the entire group, sodium restriction resulted in mean void frequency decreasing in a progressive manner upon sodium restriction from 2.9 ± 1.7 (n=94) at baseline to 2.0 ± 1.7 (76) on the first follow-up to 1.7 ± 1.2 (53) to 1.6 ± 1.3 (32) to 1.5 ± 1.2 (22) on the second through fourth follow-up visits. Among the 50 subjects with 2 follow-up visits, mean voiding frequency decreased significantly upon sodium restriction from 3.1 ± 1.6 to 2.1 ± 1.6 to 1.6 ± 1.1 on the first and second follow-up visits, respectively (p<.01). 

Changes in nocturnal voids were significantly correlated with female gender (p=.024) and baseline number of voids (r=.52, p<.001), but not with body mass index, blood pressure, creatinine or edema. There were trends with orthopnea (r=.23, p=.094), heart rate (r=.21, p=.076) and age (r=.174, p=.15). Of note, Δ void frequency was not significantly correlated with Δ blood pressure.

On multivariate analyses, change in voiding frequency was independently associated with baseline number of voids and a trend toward female gender. 

Amongst the patient visits, adherence with sodium restriction appeared to be related to greater declines in nocturnal voiding frequency.

Sodium restriction in cardiovascular patients is accompanied by a significant reduction in nocturnal voiding frequency. A greater number of baseline number of nocturnal voids appears to be predictive of a greater decline in the number of nocturnal voids upon sodium restriction. The high proportion of patients who were classified as adherent to dietary interventions refutes the notion that Δ voiding frequency is simply attributable to a phenomenon of regression toward the mean. These results implicate sodium intake as an important determinant of nocturia in patients with cardiovascular disease. Dietary modification presents an important adjunct therapy to reducing nocturia frequency.

The absolute reduction in nocturnal voiding frequency meets or exceeds that seen in currently available urologic interventions for nocturia. Notably, change in voiding frequency was not significantly correlated with change in blood pressure. The present study results underscore nocturia to be related to both free water and sodium homeostasis. More work is needed to establish the clinical predictors of nocturia severity and treatment response in cardiovascular patients.

Redeker NS, Adams L, Berkowitz R, et al. Nocturia, Sleep and Daytime Function in Stable Heart Failure. J Card Fail. 2012;18(7):569-75
Gupta D, Georgiopoulou VV, Kalogeropoulos AP, et al. Dietary Sodium Intake in Heart Failure. Circulation. 2012;126:479-85
Hashim H, Blanker MH, Drake MJ. International Continence Society (ICS) report on the terminology for nocturia and nocturnal lower urinary tract function. Neurourol Urodyn. 2019;38(2):499-508.