Sodium and Dogs

Many people add canned vegetables and meats to their dogs’ meals. Most of these have salt added although there are low-sodium canned foods as well. There was an interesting discussion on VETMED-L asking, to paraphrase, if there has been any research about whether or not dogs can get too much sodium in their diet.

List member Barbara Nibling replied to the issue with an in depth, informative response. It is reposted here with her permission and is filled with research findings.

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Ouch, well, there are probably more studies on sodium than you think. Especially in investigating the issue of kidney failure in both humans and dogs and in the issue of blood pressure in humans and dogs.  So just to roll my eyes here … “Low sodium” is a vague term – just how low is “low”?

Sodium, along with potassium and chloride, are ions and cations found in intracellular fluid.   Potassium is the main cation.   Sodium the other cation. In the intracellular fluid, it provides the primary osmotic force to maintain the fluid integrity – too little and it’s like a water balloon starting to deflate, unable to maintain the membrane – but too much and it causes pressure by occupying space beyond it’s normal boundaries.  Sodium in one of the ions that provides normal irritability of neurons and the contractibility of muscle fibers.(Deplete electrolytes = bad, right?)  The sodium “pump” controls electrolyte balance between intracellular and extracellular compartments.

The chief source of sodium in dog foods is common table salt, which provides both the sodium and chloride.  And actually foods considered naturally high in sodium are dairy products, meat, poultry, fish, and egg white. Because of its abundance, sodium is not considered a problem in dogs.

Well, of course, there have been studies …

General practice is to provide 1% sodium chloride to dry dog foods, which provides about 95 mg sodium and 147 mg chlorine per kg of bodyweight of the dog per day. That amount meets the requirement and does greatly exceed the amount required by dogs. Dogs fed less than 23 mg of sodium per kilogram of body weight showed changes in concentrations of blood-pressure regulating hormones in 3 days (Bunag et all 1966, Ganong and Boreyzka, 1967, Brubacher and Vander 1968).

Morris in 1976 fed a diet containing .0075% sodium for 23 weeks and reported no adverse effects. Similar studies by Hamlin in 1964 which inferred a low sodium requirement for the dog. Humans with inadequate sodium chloride intake are easily fatigued and McCance in 1936 and again in 1944 observed the same exercise intolerance in dogs (along with decreased utilization of protein).

But we weren’t talking about too little, but too much. Dogs have been fed a diet of 2% sodium – 190 kg sodium per kilogram of bodyweight. McCay in 1949 observed a greater than normal water intake but normal health. In observing the relationship of blood pressure and salt intake in humans, they began studying dogs – Swales in Blood pressure and the Kidney (1981) and Wilhelm et al “Effect of prolonged high sodium chloride ingestion and withdrawal upon blood pressure in dogs (1951).

It appears than the sodium pump in dogs handles a wider range of sodium concentrations in both well and ill dogs than it does in humans. While hypertension does exist in some individuals in dogs, it does not appear to be influenced by sodium or by any defect in the sodium pump itself. Data indicates that dogs are resistant to salt retention – regulating excess salt intake by excreting it through the urine – and any resultant hypertension. More studies have been done:  Spangler, Hypertension in dogs: a Review (1977); Ladd,  Response of the normal dog to dietary sodium chloride (1949); Anderson  The Blood Pressure in canine interstitial nephritis (1968).

Without a doubt, dog foods – wet, dry, canned, raw fed – contain more sodium than the dog needs. And dogs adjust quite easily to a high sodium intake, showing increased water drinking – but weight gain due to excess water retention or edema has not been observed in healthy dogs. And when that excess sodium is withdrawn to a lower level – not to a “low level” by any means given the amount of meat or poultry or kibble most dogs eat – dogs adjust quickly to lower sodium intake.

Barbara
and the corgis
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