Letter to the Editor: Revisiting salt restriction in hyponatremic cirrhosis - a paradigm in need of refinement?

Abstract

The management of decompensated cirrhosis is fraught with clinical dilemmas, often requiring a delicate balance between opposing physiological principles. One such enduring controversy is the role of dietary sodium restriction, long considered a cornerstone in the management of ascites and fluid overload. The study by Marrapu et al published in the World Journal of Methodology, directly challenges this convention in a specific and vulnerable population: Patients with cirrhosis and moderate to severe hyponatremia. Their open-label randomized controlled trial provides compelling evidence that a salt-restricted diet (5 g/day) may be harmful compared to a more liberal, salt-unrestricted diet (10 g/day), associating salt-restricted diet with a significantly higher risk of acute kidney injury, poorer nutritional and hemodynamic profiles, and increased short-term mortality, without offering a clear benefit in ascites control.

Key Words: Cirrhosis; Hyponatremia; Sodium restriction; Acute kidney injury; Sarcopenia; Nutritional status; Mortality; Dietary management

Core Tip: This study serves as a critical catalyst for re-evaluating a decades-old dietary dogma. It suggests that in cirrhotic patients with moderate to severe hyponatremia, automatic sodium restriction may inadvertently accelerate the path to renal injury, sarcopenia, and death. A more tailored, physiology-guided dietary strategy that prioritizes renal perfusion and nutritional preservation is urgently needed. This underscores the need for more individualized dietary strategies, particularly in this vulnerable patient population.

TO THE EDITOR

The study by Marrapu et al[1] published in the World Journal of Methodology clearly demonstrates a risk of acute kidney injury (AKI) with salt-restricted diet (SRD), quantifying a near five-fold increased odds. The physiological rationale for this finding is sound and aligns with the evolving understanding of circulatory dysfunction in advanced cirrhosis. Hyponatremia in this setting is not merely an electrolyte disturbance but a marker of profound effective arterial hypovolemia, driven by splanchnic vasodilation and non-osmotic vasopressin release[2]. In this context, further intravascular volume depletion induced by stringent sodium restriction can exacerbate renal hypoperfusion, precipitating AKI - a well-established harbinger of mortality[3]. This corroborates earlier work by Gu et al[4], which suggested liberal salt intake could improve renal blood flow in cirrhotic patients with ascites. The current study extends this observation specifically to hyponatremic patients, a subgroup likely most sensitive to volume perturbations.

Equally important are the findings related to nutrition and sarcopenia. Cirrhosis is a catabolic state, and malnutrition/sarcopenia independently predict morbidity and mortality[5]. The study demonstrates that SRD was associated with worse handgrip strength, a key marker of sarcopenia, and trends toward lower mid-arm circumference and serum albumin[1]. This is clinically intuitive, as unpalatable low-salt diets can reduce overall food intake. Furthermore, sodium plays a crucial role in the coupled intestinal absorption of nutrients like glucose and amino acids[6]. Thus, excessive salt restriction might not only reduce intake but also impair the absorption of what is consumed, creating a double nutritional insult. The significantly higher mortality in the SRD group (54.9% vs 29.6%) is a sobering endpoint that likely stems from this confluence of worsened renal function and nutritional decline[1].

The study’s conclusion that SRD offered no significant advantage in ascites control is particularly noteworthy. Traditional teaching holds that sodium retention is the primary driver of ascites formation. However, this trial adds to a growing body of literature questioning the efficacy of strict restriction. Older and more recent studies alike have failed to consistently show a benefit, with some even indicating worse outcomes[4,7]. As Marrapu et al[1] discuss, sodium depletion may impair diuretic response and reduce renal perfusion pressure, paradoxically hindering ascites mobilization. Their subgroup analysis suggesting better ascites control in patients who remained AKI-free reinforces the idea that preserving renal function may be more critical for fluid management than rigid sodium restriction.

DECONSTRUCTING THE PATHOPHYSIOLOGY: WHY SALT RESTRICTION CAN BE THE WRONG LEVER

To understand the findings of Marrapu et al[1], one must move beyond the textbook model of simple sodium retention. The circulatory state of advanced, decompensated cirrhosis is a complex and maladaptive cascade. Profound splanchnic arterial vasodilation, driven by local vasodilators like nitric oxide, creates a massive downstream “sump”. This leads to a marked reduction in effective arterial blood volume - the volume sensed by high-pressure baroreceptors - despite an increase in total blood volume sequestered in the splanchnic circulation. This effective hypovolemia is the primary driver, activating powerful compensatory systems: Renin-angiotensin-aldosterone system, the sympathetic nervous system, and non-osmotic release of arginine vasopressin. While arginine vasopressin contributes to water retention and hyponatremia, the activated renin-angiotensin-aldosterone system and sympathetic tone cause intense renal vasoconstriction.

In this precarious setting, the kidneys are perpetually on the brink of hypoperfusion. The primary clinical goal should be to support renal perfusion pressure. Dietary sodium restriction, however, pulls the lever in the opposite direction. By limiting sodium intake, we reduce the osmotic driving force for retaining fluid within the intravascular compartment. This can exacerbate the effective hypovolemia, further amplifying the signals for renal vasoconstriction. The study by Marrapu et al[1] provides direct clinical evidence for this sequence: The SRD group had consistently lower mean arterial pressure (MAP) throughout follow-up[5]. Even modest reductions in MAP in cirrhosis have been strongly linked to AKI risk. Cullaro et al[7] demonstrated that in outpatients with cirrhosis, a time-updated MAP was inversely associated with the risk of both AKI and mortality, suggesting it as a modifiable therapeutic target. Maiwall et al[8] in the TARGET-C trial, showed that targeting a higher MAP (≥ 75 mmHg vs ≥ 65 mmHg) in cirrhotic patients with septic shock improved 28-day survival, underscoring the importance of perfusion pressure in this population.

Therefore, a liberal sodium intake, as in the salt-unrestricted diet (SUD) group, may act as a physiological “prop”, helping to maintain intravascular volume and, consequently, renal perfusion pressure. This aligns with the earlier work of Gu et al[4], who used Doppler ultrasonography to show that a liberal sodium diet (equivalent to the SUD in Marrapu et al’s study[1]) improved renal resistive indices and renal blood flow in cirrhotic patients with ascites compared to a restricted diet. The kidney in advanced cirrhosis is exquisitely sensitive to perfusion pressure; sodium restriction removes a key substrate for maintaining that pressure, tipping the balance towards ischemia and AKI.

METHODOLOGY AND DATA SOURCES

The study by Marrapu et al[1], while provocative, has inherent methodological limitations that warrant a balanced interpretation. The open-label design introduces potential bias, and dietary adherence assessment remains a perennial challenge in nutritional studies. The high attrition rate, typical in studies of advanced cirrhosis, may have underpowered some secondary analyses. Furthermore, the baseline imbalance in sex distribution, though reportedly not affecting outcomes, is a notable point. Importantly, the findings apply specifically to patients with hyponatremia (Na < 130 mEq/L) and should not be extrapolated to all cirrhotic patients with ascites. These considerations suggest that the results should be viewed as hypothesis-generating, requiring confirmation in more rigorously designed trials.

How, then, should clinicians integrate these findings into practice? A blanket, one-size-fits-all prescription of strict sodium restriction is increasingly untenable. The study by Marrapu et al[1], alongside others[4,8], advocates for a nuanced, individualized approach. For the hyponatremic cirrhotic patient, a moderately liberal sodium intake (e.g., aligning with the study’s SUD of approximately 10 g/day, which is close to the average Indian intake[9] and the global population average) appears safer, potentially preserving renal function and nutritional status without exacerbating ascites. The goal should shift from “sodium restriction at all costs” to “optimal sodium intake for hemodynamic and nutritional stability”. This necessitates careful monitoring of renal function, nutritional parameters, and fluid status.

LIMITATIONS AND FUTURE DIRECTIONS

The study by Marrapu et al[1] has limitations, which the authors appropriately acknowledge. The open-label design is a major one, though blinding a dietary intervention is notoriously difficult. Dietary adherence was assessed by recall, which is imperfect. The high attrition rate reflects the real-world challenge of studying very sick patients but may have impacted some secondary analyses. The baseline sex imbalance, though reportedly not affecting outcomes, is notable. Importantly, the findings are most robust for the specific population studied: Cirrhotics with hyponatremia without AKI at baseline. Generalization to all ascitic patients requires caution. Furthermore, despite statistical adjustments, the potential for residual confounding from unmeasured variables such as subclinical infections or variations in concomitant medication use cannot be entirely excluded. Therefore, while the findings are robust within the study’s context, their definitive clinical impact and generalizability await confirmation in larger, more rigorously designed trials.

These limitations point directly to critical avenues for future research: (1) Larger multicenter randomized controlled trials: Confirmatory trials in diverse populations are needed. Ideally, these would employ creative methods to improve blinding (e.g., providing all meals) and use objective adherence biomarkers; (2) Biomarker discovery: We desperately need reliable biomarkers to assess “effective intravascular volume” and “salt sensitivity” in cirrhosis. Perhaps novel imaging techniques, hormonal panels, or even assessment of tissue sodium content via 23Na-magnetic resonance imaging could guide therapy; (3) Precision nutrition trials: Moving beyond “SRD vs SUD”, future studies should test algorithm-driven, personalized sodium prescriptions based on continuous streams of data (vitals, labs, bioimpedance) to dynamically optimize intake; and (4) Mechanistic studies: Further exploration of the link between sodium intake, gut microbiome, systemic inflammation, and vascular reactivity in cirrhosis is warranted.

Future research should prioritize validating these findings in larger, multicenter, and where feasible, double-blind trials. Exploring objective biomarkers of sodium intake and volume status in cirrhosis is crucial. Studies are also needed to define optimal sodium thresholds for different cirrhosis subgroups, perhaps incorporating assessments of “salt sensitivity” or non-osmotic sodium storage[10].

CONCLUSION

In conclusion, the work by Marrapu et al[1] serves as a critical catalyst for re-evaluating a decades-old dietary dogma. It suggests that in cirrhotic patients with moderate to severe hyponatremia, automatic sodium restriction may inadvertently accelerate the path to renal injury, sarcopenia, and death. Importantly, these findings are specific to this high-risk subgroup and should not be generalized to all cirrhotic patients with ascites. A more tailored, physiology-guided dietary strategy that prioritizes renal perfusion and nutritional preservation is urgently needed. It is time to season our clinical guidelines with a generous pinch of individualization and evidence. This underscores the need for larger confirmatory studies and the development of personalized nutritional guidelines in advanced liver disease.

ACKNOWLEDGEMENTS

We acknowledge the support and cooperation of all the study participants.