The chicken-or-egg dilemma with nocturia: which matters most, the water or the salt?

Most individuals with nocturia have tried at some time limiting their water intake, or even cutting out all fluid intake after 4 pm, in an effort to urinate less at night. They got this idea from the internet, as advice from a medical provider, or it just seemed a practical solution. Published literature (1,2) offers modest justification of this fluid management strategy, either involving cutting one’s daily fluid intake by 25% or 50% (1) or going from a baseline intake of 1.7 liters to 1.3 L (2). Most often, I hear from patients that decreasing fluid intake, often in the face of being slightly dehydrated and thirsty, is unpleasant leaving them uncomfortable at best and occasionally constipated and with a dark, malodorous urine.

Interest has been growing in viewing nocturia treatment as equally as much a salt problem as a water problem. Instead of guidance solely on fluids, patients would be counseled on reducing their sodium intake for reduction in nocturia. This is biologically-plausible, and perhaps less objectionable than denying oneself fluids. In this issue of the Journal of Clinical Hypertension, Monaghan, et al. (3), report on their clinical series of patients in a cardiology clinic where they offered clinician screening, assessment and instruction on reducing sodium intake to also reduce nocturia. This study is not the first published article supporting this approach: excessive intake of sodium has been demonstrated to be associated with nocturia (4), and early experimental evidence in patients with high salt intake (5) has shown reductions in nocturia.

The authors of this article are experienced, thoughtful clinicians and scientists who have drawn on their research and clinical work to implement a practical intervention. Patients were asked about nighttime disruption of sleep and if they were going to the bathroom to urinate at night. More than just a blanket statement of “eat less salt”, patients’ diets were reviewed using a per-item breakfast, lunch, dinner, and snack dietary history. This approach identified not only salt, but also seasoned salt and foods and condiments high in sodium, including processed and cured meats, chicken bouillon, and sauces that were common items in the diets of their inner-city practice patients. Patients were then offered education, counseling, and an individualized treatment plan. The authors found that those patients who self-reported success in reducing sodium intake had more significant reductions in nocturia than those who did not. The degree of reduction in nocturia was statistically significant, and of a degree that would likely be of importance to the patient. There were likely other health benefits as well.

By no means is this a perfect study, and the authors properly frame it strengths and limitations. For me, the study strengths are that it seems plausible and feasible, integrated into a busy practice setting by those working clinically within the practice. The baseline characteristics of the patients do not seem to suggest a singular diagnostic category (e.g., not simply only patients with heart failure), so this approach might meaningfully extend more broadly to patients with cardiovascular disease seen in a primary care clinic. Many of the patients were African-American women (93% African American, 77% women), a population that has been shown to have higher rates of nocturia (6, 7), and this helps extend earlier work that was largely with Japanese patients (4, 5). There also in this trial were limited exclusion criteria (those with benign prostatic hypertrophy, urge urinary incontinence, or overactive bladder were not excluded), suggesting that sodium reduction might have broader applicability. Success with the intervention was determined by the patient’s self-reported adherence to the specific dietary plan, and did not depend on the ongoing completion of food diaries or weekly monitoring of urine for sodium (5). For me, a couple of study weaknesses temper my thoughts about easy reproducibility in my clinic. Some of the participants had very little nighttime voiding at baseline, and may be different from many patients seeking care for nocturia. There was not a standardized question for nocturia, but rather patients were asked if they slept through the night. The dietary interventions were delivered by an expert physician with several other tasks to complete; a protocol and implementation guide would make this more exportable.

Given the trial design, this work offers limited insight into how this treatment is effective, making this more useful as a hypothesis generating study and implementation trial. Not surprisingly to me, nocturia reductions came without obvious differences in blood pressures measured in clinic. By parallel example, nocturia is known to be associated with diabetes mellitus in epidemiologic studies (8), yet many patients acceptable diabetic control still have nocturia (9). Perhaps ambulatory monitoring or nocturnal recording might show reductions in average blood pressure or restoration of nighttime dipping (10). I also wanted more information about peripheral edema. For me, I believe that previous trial results from Matsuo, et al, (5) help with identifying some likely mechanisms. In that study, they used morning spot urine samples for sodium to categorize success with reduction in salt. For those with decreased sodium intake (versus no reduction), there was decreased 24 hour fluid intake (from 2.2 L to 2.0 L, versus the comparison group that increased from 2.3 L to 2.5 L), a decreased 24 hour urine output (2.3 L to 2.2 L versus 2.3 L to 2.6 L), and a reduced percentage of urine excreted during the night (28% versus 30%) as an overall percentage of 24 hour urine output (4).

I want to offer my patients with nocturia a highly-efficacious, individualized, inexpensive, and side-effect free therapy. I further hope that this treatment could be easily explained by me or my team. The patient could easily understand the treatment and rationale, and would then offer a preference for this approach, go home and successfully implement the intervention. So many existing treatments fall short on one or more of the above criteria. Notably, patients receiving this sodium reduction approach would all not have met criteria for use of desmopressin analogues (11, 12) because of contraindications (heart failure was a comorbid condition in 40%, loop diuretics were used by 43%, and many had uncontrolled hypertension and chronic kidney disease) or may have had a need for more frequent monitoring (age over 65, and 20% on thiazide diuretics).

To me, and particularly for the older patients that I treat, I see favoring sodium reduction approaches over fluid restriction approaches. I will work to integrate this approach into my practice and research. I feel that this could be a component of a multicomponent intervention that would work with other related interventions such as other behavioral approaches (13) and interventions for sleep hygiene (14), compression stockings for leg swelling (15, 16), and gentle management of fluid timing (13). I would want a standardized, patient completed questionnaire to see if this approach be easily integrated into routine clinical practice (time, expertise, patient-completed instruments). Based upon this report, my enthusiasm is high for integrate screening, assessing, and intervening on dietary sodium in my practice and research settings with patients with nocturia.