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==1. What is Sodium?==

==What is Sodium?==

Sodium is the principal cation (positive ion) of the extracellular fluids, where it is usually in combination with the chloride anion (negative ion) forming sodium chloride (common salt). Sodium does not exist in its free state in nature but is combined with other elements to form salts.

Sodium is the principal cation (positive ion) of the extracellular fluids, where it is usually in combination with the chloride anion (negative ion) forming sodium chloride (common salt). Sodium does not exist in its free state in nature but is combined with other elements to form salts.

==2. Why is it Important?==

==Why is it Important?==

Sodium is indispensable for the regulation of acid-base balance and osmotic pressure. Its other main role is maintaining the membrane potential in nerve and muscle tissues thereby facilitating the generation and transmission of electrical impulses.

Sodium is indispensable for the regulation of acid-base balance and osmotic pressure. Its other main role is maintaining the membrane potential in nerve and muscle tissues thereby facilitating the generation and transmission of electrical impulses.

==3. Roles in the Body==

==Roles in the Body==

Sodium is distributed in bone (43%) interstitial fluid (29%) and plasma (12%). The concentration of sodium (i.e., sodium chloride) in blood is approximately 0.9%. The main hormone involved in sodium balance is aldosterone, which is released by the adrenal glands in response to a low plasma sodium concentration. Aldosterone acts by increasing the renal retention of sodium.

Sodium is distributed in bone (43%) interstitial fluid (29%) and plasma (12%). The concentration of sodium (i.e., sodium chloride) in blood is approximately 0.9%. The main hormone involved in sodium balance is aldosterone, which is released by the adrenal glands in response to a low plasma sodium concentration. Aldosterone acts by increasing the renal retention of sodium.

The high level of sodium in extracellular fluids is responsible for establishing a concentration gradient across cell membranes. Sodium attracts water molecules when in solution, and the size of the hydrated sodium ion prevents it crossing cell membranes as easily as other ions such as potassium and chloride. This means that the permeability of the membrane to sodium is generally very low but when there is a momentary change in the membrane’s permeability, sodium is driven into the cell and this dramatically alters the membrane potential from negative to positive. This change – the action potential – is responsible for nervous activity. The extra sodium in the cell is then removed by active transport via a sodium pump, which is energy dependent, and this restores the system to its resting state.  

The high level of sodium in extracellular fluids is responsible for establishing a concentration gradient across cell membranes. Sodium attracts water molecules when in solution, and the size of the hydrated sodium ion prevents it crossing cell membranes as easily as other ions such as potassium and chloride. This means that the permeability of the membrane to sodium is generally very low but when there is a momentary change in the membrane’s permeability, sodium is driven into the cell and this dramatically alters the membrane potential from negative to positive. This change – the action potential – is responsible for nervous activity. The extra sodium in the cell is then removed by active transport via a sodium pump, which is energy dependent, and this restores the system to its resting state.  

      

      

==4. Consequences of Sodium Deficiency==

==Consequences of Sodium Deficiency==

===Dog:===   

===Dog:===   

As with [[Potassium - Nutrition|potassium]], naturally-occurring sodium deficiency is rare in dogs but when fed diets very low in salt content adverse effects have been observed.

As with [[Potassium - Nutrition|potassium]], naturally-occurring sodium deficiency is rare in dogs but when fed diets very low in salt content adverse effects have been observed.

Clinical findings of sodium deficiency were observed in 12- to 15-week old kittens fed a diet with a sodium content of 0.01% DM and included anorexia, excessive thirst, increases in haemoglobin concentration, plasma aldosterone and urine volume, and impaired growth. When dietary sodium was increased to 0.2% DM, normal health was restored<ref>Yu, S, Morris, J (1997). “The minimum sodium requirement of growing kittens defined on the basis of plasma aldosterone concentration”. J. Nutr. 127:494-501.</ref>.

Clinical findings of sodium deficiency were observed in 12- to 15-week old kittens fed a diet with a sodium content of 0.01% DM and included anorexia, excessive thirst, increases in haemoglobin concentration, plasma aldosterone and urine volume, and impaired growth. When dietary sodium was increased to 0.2% DM, normal health was restored<ref>Yu, S, Morris, J (1997). “The minimum sodium requirement of growing kittens defined on the basis of plasma aldosterone concentration”. J. Nutr. 127:494-501.</ref>.

==5. Toxicity==

==Toxicity==

====Dog:====   

====Dog:====   

The main adverse effect of excessive sodium intake is an increased potassium excretion resulting in a negative potassium balance. A sodium content of 2.9% DM fed to adult dogs caused vomiting and food aversion<ref>Zentek, J, Meyer, H (1995). “Normal handling of diets – Are all dogs created equal?”. J. Sm. Anim. Pract. 36:354-359.  </ref>. However, given an adequate supply of water, dogs can cope with a wide range of sodium intakes and dietary levels up to 1.5% DM are deemed acceptable<ref>Boemke, W, Palm, U, Kaczmarczyk, G, Reinhardt, H (1990). “Effect of high sodium and high water intake on 24-h potassium balance in dogs”. J. Exper. Anim. Sci. 33:179-185.</ref>.

The main adverse effect of excessive sodium intake is an increased potassium excretion resulting in a negative potassium balance. A sodium content of 2.9% DM fed to adult dogs caused vomiting and food aversion<ref>Zentek, J, Meyer, H (1995). “Normal handling of diets – Are all dogs created equal?”. J. Sm. Anim. Pract. 36:354-359.  </ref>. However, given an adequate supply of water, dogs can cope with a wide range of sodium intakes and dietary levels up to 1.5% DM are deemed acceptable<ref>Boemke, W, Palm, U, Kaczmarczyk, G, Reinhardt, H (1990). “Effect of high sodium and high water intake on 24-h potassium balance in dogs”. J. Exper. Anim. Sci. 33:179-185.</ref>.

There is little if any information on the adverse effects of high sodium intakes in cats. Yu et al.<ref>Yu, S, Rogers, Q, Morris, J (1997). “Absence of salt (NaCl) preference or appetite in sodium-replete or depleted kittens”. Appetite 29:1-10.</ref> reported that, although kittens showed an aversion to a diet containing sodium at 1% DM when given a choice, they consumed it in normal amounts with no adverse effects when it was the only diet available.  Burger<ref>Burger, I (1979). “Water balance in the dog and cat”. Pedigree Digest 6:10-11.</ref> reported that adult cats receiving dietary sodium up to 1.5% DM showed no abnormalities. These values are similar to those reported for dogs and, as with dogs, assume adequate amounts of water are available.

There is little if any information on the adverse effects of high sodium intakes in cats. Yu et al.<ref>Yu, S, Rogers, Q, Morris, J (1997). “Absence of salt (NaCl) preference or appetite in sodium-replete or depleted kittens”. Appetite 29:1-10.</ref> reported that, although kittens showed an aversion to a diet containing sodium at 1% DM when given a choice, they consumed it in normal amounts with no adverse effects when it was the only diet available.  Burger<ref>Burger, I (1979). “Water balance in the dog and cat”. Pedigree Digest 6:10-11.</ref> reported that adult cats receiving dietary sodium up to 1.5% DM showed no abnormalities. These values are similar to those reported for dogs and, as with dogs, assume adequate amounts of water are available.

==6. Dietary Sources==

==Dietary Sources==

Although sodium is found widely in nature, the main sources are derived from animal materials such as meat meal, meat and bone meal, fish meal and blood meal. These will generally be sufficient to supply the nutritional requirement in dog and cat foods. Nevertheless, there are several mineral salts that are commonly used to supply sodium such as the sodium salts of [[Chloride - Nutrition|chloride]], carbonate, bicarbonate, phosphate and sulphate.

Although sodium is found widely in nature, the main sources are derived from animal materials such as meat meal, meat and bone meal, fish meal and blood meal. These will generally be sufficient to supply the nutritional requirement in dog and cat foods. Nevertheless, there are several mineral salts that are commonly used to supply sodium such as the sodium salts of [[Chloride - Nutrition|chloride]], carbonate, bicarbonate, phosphate and sulphate.