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Understanding Fluid and Electrolyte Balance

Fitday Editor
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In the body, when fluid levels change in response to either becoming dehydrated or overhydrated, levels of certain minerals, called electrolytes, can be thrown out of balance, such as sodium, potassium, and calcium. Understanding the causes and the symptoms can help bring the body back into balance before serious health consequences occur.


The body is made up of about 60% water. About two-thirds of the fluid is located inside the cells and about 8% is in the bloodstream. Basically, when water intake equals water loss, the body is in fluid balance.

Dehydration is the condition of not having enough water and can occur with vomiting, diarrhea, diuretics, excessive heat, excessive sweating, fever, or decreased water intake. Overhydration is a state of excess body water. Although it can occur from drinking too much water, this isn't likely when the rest of the body is functioning properly. It usually occurs in people with heart conditions (congestive heart failure), kidney failure, or liver disease.


When sodium is too low in the body, the medical term for the condition is hyponatremia. This usually occurs when a person has too much fluid, which dilutes the level of the amount of sodium in the body. Poorly controlled diabetes can also lead to hyponatremia. It is possible that it can result from not getting enough sodium in the diet, but this is not typically of most Americans. Low sodium can cause confusion, drowsiness and muscle weakness. Severe hyponatremia can lead to seizures.

When blood levels of sodium are too high, called hypernatremia, and is usually caused by a loss of body water or dehydration. It can occur with the use of diuretics, commonly prescribed for high blood pressure or congestive heart failure. The first symptom is usually thirst, followed by weakness and fatigue. If a high sodium level is not treated, it can lead to confusion, paralysis and coma. An increase in fluids is usually prescribed.


Low potassium is called hypokalemia. It is most often caused by the use of a diuretic which causes the kidneys to excrete potassium. It can also occur with prolonged diarrhea or vomiting. Low potassium can cause fatigue, confusion or muscle weakness. If left untreated, it can also lead to abnormal heart rhythms. Doctors will usually prescribe potassium supplements to correct the problem.

A high potassium level, hyperkalemia, is usually caused by kidney failure or the use of a drug that causes the kidneys to retain fluid. The first symptom is usually an abnormal heart rhythm. People with a chronic condition such as kidney failure are usually instructed to eat a low potassium diet, excluding foods such as potatoes and bananas. If the potassium level is dangerously high, intravenous calcium is given plus a diuretic that helps the kidneys to excrete the potassium in the urine.


Calcium is known as a bone building nutrient, but it is also very important in fluid and electrolyte balance. A low calcium level, hypocalcemia can result when a widespread infection in the blood called sepsis develops suddenly. It can also result from the dysfunction or removal of the parathyroid gland, a deficiency in vitamin D, or with a disorder of the thyroid gland or pancreas. Low calcium levels cause a person to feel weak and numbness may occur in the hands or feet.

High calcium levels, hypercalcemia, is caused by the breakdown of bone which releases calcium into the blood stream. An excess in the amount of parathyroid hormone can also high blood calcium levels. A slightly high level typically does not cause symptoms, but a very high level can cause dehydration, loss of appetite, nausea and vomiting. Drugs are available to decrease the amount of calcium released from the bones.

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