Can More Dietary Sodium Help Prevent Feline Urolithiasis?

For years, dietary sodium has been viewed cautiously in companion animal nutrition, with concerns that excessive sodium intake may adversely affect health. However, emerging evidence suggests that controlled sodium supplementation in therapeutic urinary diets may actually play a beneficial role in reducing the risk of both calcium oxalate (CaOx) and struvite urolith formation by increasing urine dilution¹. 

For practicing veterinarians, this represents an important shift in thinking. Rather than focusing solely on urine pH or mineral restriction, modern nutritional management increasingly emphasizes maximizing urine volume as one of the most effective strategies for lowering urinary supersaturation (RSS)—the driving force behind crystal and stone formation¹. 

Why Does Urine Dilution Matter? 

The formation of urinary calculi depends on the concentration of stone-forming minerals within the urine. When urine becomes concentrated, minerals such as calcium, oxalate, magnesium, phosphate and ammonium are more likely to exceed their solubility limits and crystallize. Conversely, increasing urine volume dilutes these minerals, reducing the likelihood of crystal formation¹. 

One practical way to achieve this is by encouraging greater water intake. While feeding canned diets remains an effective strategy, recent research demonstrates that carefully increasing dietary sodium in dry therapeutic diets can also stimulate voluntary water consumption, resulting in larger urine volumes and lower urine specific gravity (USG)¹. 

What Does the Evidence Show? 

In a controlled feeding study, Queau and colleagues evaluated four dry diets containing progressively increasing sodium concentrations ranging from 0.67 to 3.27 g/1,000 kcal in healthy cats¹. 

As dietary sodium increased: 

• Water intake increased significantly.

• Urine volume nearly doubled compared with the lowest sodium diet.

• Urine specific gravity decreased progressively.

• Urinary concentrations of calcium, oxalate, magnesium, phosphate and ammonium all declined significantly¹.

These changes translated into a substantial reduction in relative supersaturation (RSS) for both calcium oxalate and magnesium ammonium phosphate (struvite), suggesting a lower biochemical risk for stone formation¹. 

Importantly, the reduction in RSS occurred consistently despite normal individual variation among cats. 

Lower Relative Supersaturation Means Lower Stone Risk 

Relative supersaturation (RSS) is widely accepted as one of the best laboratory indicators of the likelihood that urinary crystals will form. Although RSS does not predict exactly when a stone will develop, reducing RSS decreases the physicochemical environment that favours crystal nucleation and growth¹. 

In this study, cats consuming the highest sodium diet had markedly lower CaOx RSS and struvite RSS than those fed the lowest sodium diet¹. This improvement was primarily attributed to urinary dilution, which lowered the concentration of stone-forming ions. 

For clinicians, this reinforces an important concept: 

The goal is not simply to alter urine chemistry—it is to create dilute urine in which crystals are less likely to form. 

Does Increased Sodium Increase Urinary Calcium? 

One longstanding concern has been that higher sodium intake might increase urinary calcium excretion and inadvertently promote calcium oxalate stone formation, as has been reported in human medicine. 

Interestingly, the feline data tell a different story. 

Although urinary sodium concentrations increased appropriately with dietary sodium intake, urinary calcium concentration actually decreased because of the accompanying increase in urine volume¹. Consequently, calcium oxalate RSS declined rather than increased. 

This finding suggests that, in healthy cats fed appropriately formulated therapeutic diets, the benefits of urine dilution outweigh any potential effects of increased sodium intake on calcium handling¹. 

Is Sodium the Only Way to Achieve Urine Dilution? 

Probably not. 

While dietary sodium has traditionally been used to encourage voluntary water intake, newer research suggests that potassium chloride (KCl) may offer another nutritional approach to achieving the same therapeutic goal². In a controlled study involving healthy cats, increasing dietary potassium chloride significantly increased water intake and urine volume while reducing urine specific gravity². Importantly, calcium oxalate relative supersaturation also decreased, indicating a lower biochemical risk for stone formation². 

Unlike sodium supplementation, potassium chloride achieved urine dilution without increasing dietary sodium intake. The urinary concentrations of most stone-forming minerals either remained unchanged or decreased as a consequence of increased urine volume². These findings reinforce an important clinical principle: it is the production of consistently dilute urine—not sodium itself—that reduces the urinary environment favourable for crystal formation². 

Although these results are encouraging, the study was performed in healthy animals over a short period. Further prospective studies in cats with naturally occurring urolithiasis are needed before potassium-enriched therapeutic diets can be recommended routinely for stone prevention². 

Should High-Sodium Diets Be Recommended for Every Cat? 

Not necessarily. 

The sodium study evaluated healthy cats over a short period, demonstrating improvements in urine composition and stone risk indices rather than actual reductions in stone recurrence¹. Similarly, evidence supporting potassium chloride is currently limited to short-term physiological studies². Longer-term clinical trials in cats with naturally occurring urolithiasis are still required before broad recommendations can be made¹². 

Furthermore, dietary sodium supplementation should not be viewed as a standalone preventive strategy. Successful long-term management still depends on: 

• Maintaining adequate water intake.

• Feeding an appropriate urinary therapeutic diet.

• Monitoring urine specific gravity and routine urinalysis.

• Identifying the stone type whenever possible.

• Addressing underlying metabolic disorders in recurrent calcium oxalate stone formers.

Clinical Take-Home Messages 

• Controlled dietary sodium supplementation can significantly increase voluntary water intake and urine volume in cats, leading to more dilute urine¹.

• Increased urine volume lowers urine specific gravity and reduces the relative supersaturation of both calcium oxalate and struvite by diluting stone-forming minerals¹.

• In healthy cats, higher dietary sodium did not increase calcium oxalate risk; instead, calcium oxalate RSS decreased because urine became more dilute¹.

• Emerging evidence suggests that potassium chloride may also promote urine dilution and lower calcium oxalate RSS without increasing dietary sodium, making it a promising future nutritional strategy for selected patients².

• Regardless of the dietary approach used, the primary therapeutic objective is to maintain consistently dilute urine through appropriate nutrition, hydration and ongoing monitoring.

As our understanding of feline urolithiasis evolves, nutritional management is moving beyond simple urine acidification. Current evidence suggests that urine dilution is the principal therapeutic target, whether achieved through increased dietary moisture, carefully formulated sodium supplementation or emerging nutritional approaches such as potassium chloride. By focusing on reducing urinary supersaturation rather than manipulating individual minerals alone, veterinarians can adopt a more evidence-based strategy to reduce the risk of recurrent urinary stone formation. 

References 

1. Queau Y, Bijsmans ES, Feugier A, Biourge VC. Increasing dietary sodium chloride promotes urine dilution and decreases struvite and calcium oxalate relative supersaturation in healthy dogs and cats. Journal of Animal Physiology and Animal Nutrition. 2020 Sep;104(5):1524-30. https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpn.13329

2. Bijsmans E, Quéau Y, Biourge V. Increasing dietary potassium chloride promotes urine dilution and decreases calcium oxalate relative supersaturation in healthy dogs and cats. Animals. 2021 Jun 17;11(6):1809. https://www.mdpi.com/2076-2615/11/6/1809