Potassium - Nutrition
What is Potassium?
Potassium is the eighth most abundant element in the body and is the second most abundant cation (positive ion) after calcium. It is found in greatest amounts in intracellular fluid – about 90% of the body’s potassium is present here and it accounts for about 75% of the cations within the body cells. Smaller quantities are found in bone, plasma, interstitial fluid and connective tissue. It is a very strong reducing metal and therefore not found in its free state in nature but combined with other elements to form salts, as described in section 6 [WikiVet Link – Section 6].
Why is it Important?
Potassium has many functions, notably in acid-base regulation, nerve impulse transmission, muscle contraction, and carbon dioxide and oxygen transport. It is also an activator or cofactor in many enzyme reactions.
Roles in the Body
Potassium within cells interacts with sodium outside cells to form a concentration gradient that maintains acid-base balance and facilitates electrical and chemical activity. This accounts for its importance in nerve impulses and muscle contraction and its role in normal cardiac function. It is also involved in protein synthesis and the uptake of amino acids. The trans-cellular potassium-sodium gradient is actively maintained by an energy-dependent system that drives cellular pumps responsible for the transport of potassium and sodium ions.
Consequences of Dietary Potassium Deficiency
Naturally-occurring dietary potassium deficiency is rare in dogs and most studies that have investigated low levels have used specially designed diets.
- Paralysis and poor growth: Puppies fed a very low level of potassium (0.01% on a dry matter basis – DM) grew very poorly and within a few weeks developed clinical signs including paralysis of the neck muscles and of the rear legs . Increasing the dietary potassium to 0.34% DM ameliorated the adverse effects.
- Hypokalaemia: Feeding adult bitches a diet containing 0.006% DM potassium did not result in detectable hypokalaemia nor were clinical signs associated with hypokalaemia seen; however, there were decreases in blood pressure, cardiac output, stroke volume and renal blood flow. A dietary potassium of 0.45% DM resulted in no detected abnormality .
The effects of low dietary potassium intake are broadly similar to those observed in dogs in terms of the syndromes described above. However, in cats there are data that show the influence of dietary protein content on potassium requirement: high protein increases potassium requirement because of an increased need for anion-cation balance .
Recognised Syndromes Related to Dietary Potassium Deficiency
- Paralysis and poor growth: Kittens fed a 33% protein diet with 0.1 or 0.2% potassium or a 68% protein with 0.3 or 0.4% potassium (all on DM basis) developed clinical signs very similar to those seen in puppies: anorexia, retarded growth and neurological disorders that started with the neck muscles and progressed to ataxia and muscle weakness. The latter was so severe that the kittens were unable to walk . Clinical signs of potassium deficiency have also been reported in kittens fed a vegetarian diet containing potassium at 0.08 or 0.11% DM, whereas a dietary content of 0.5% was satisfactory .
- Hypokalaemia: In two studies Dow et al., [5,6] reported that adult cats showed signs of hypokalaemia (Picture of cat with ventral neck flexion) when fed levels of 0.34% or 0.2% DM, which gradually disappeared with a dietary potassium concentration of 0.65% DM.
There is virtually no information on the adverse effects of excessive dietary potassium intake in dogs or cats. As potassium absorption in the intestines is very high (>90%), it would be feasible to see life-threatening hyperkalaemia if excessive amounts of potassium were found in the diet. However, the amount of potassium (in the forms of salts) required to cause toxicity would results in diets that would not be readily consumed by dogs or cats. Additionally, animals with normal kidney function should readily excrete unnecessary potassium. If potassium acts on dogs and cats in a similar way to other non-ruminant mammals, the main symptoms would be increased water intake and urine volume, food aversion and gastroenteritis. Nevertheless it would require intakes many times the recommended level to produce these effects. A tolerable dietary content of at least 1% DM is suggested for non-ruminants including dogs and cats .
Potassium is very widely distributed in nature. Good sources are meat and fish, dairy products, cereal grains and certain vegetables such as peas and potatoes. Given the ubiquitous nature of potassium, the major ingredients used in dog and cat foods, such as meats, fish and cereals, usually contain sufficient amounts to meet nutritional requirements. However supplemental sources commonly used are potassium salts such as carbonate, bicarbonate, chloride and sulphate.