Potassium and sodium work together to control the body's water balance, pH level, blood pressure and the transmission of electrochemical impulses. An imbalance of one of these two minerals often causes an imbalance of the other. For this reason, the signs and symptoms of either too much sodium or too little potassium are very similar. According to James F. Balch, M.D., author of "Prescription for Nutritional Healing", an imbalance between sodium and potassium can lead to heart disease.
Abnormal potassium levels, whether too high or too low, have a significant effect on the contractions of the heart which can be detected on an electrocardiogram (ECG). Known as cardiac dysrhythmias, these effects can, ultimately, lead to cardiac arrest. Common cardiac symptoms include fluctuations in heartbeat, high cholesterol or low blood pressure.
Having potassium levels that are too low causes muscles to become less responsive to stimuli which may cause noticeable fatigue and muscle weakness in the legs, as well as poor reflexes, muscle twitches and leg cramps. Paresthesias may develop, which causes a feeling of "pins and needles" (usually in the toes, fingers or legs). Similarly, high sodium levels often manifests as weakness, as well as lethargy and agitation.
Low potassium levels cause decreased digestive tract motility, which can result in decreased appetite, anorexia, constipation, nausea and, in severe cases, vomiting.
In cases of serious potassium deficiency, the respiratory muscles weaken, leading to shallow breathing and respiratory distress.
In severe cases of potassium deficiency, kidney function may be impaired due to an inability to concentrate the urine, causing increased urine output and protein in the urine. Low potassium also leads to salt retention, which causes elevated sodium levels that can lead to insatiable thirst.
When sodium levels are too high, there is usually increased thirst and the tongue and mucosa become dry and sticky. The excess of water outside of the cells causes oedema, or swelling, of the extremities and elevated blood pressure. If high sodium levels are caused by fluid loss due to lack of ADH, then urine output is high; otherwise, urine output is low.
Low potassium levels are also associated with headaches, impaired growth, insomnia, depression, cognitive impairment, acne, dry skin, chills and glucose intolerance. High sodium levels can lead to liver and kidney disease. (See References 1)