Electrolytes

Electrolytes are ions that form when salts dissolve in water or fluids. These ions have an electric charge. Positively charged ions are called cations. Negatively charged ions are called anions. Electrolytes are not evenly distributed within the body, and their uneven distribution allows many important metabolic reactions to occur. Sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl^-), phosphate (HPO₄^2-), bicarbonate (HCO^3-), and sulfate (SO₄^2-) are important electrolytes in humans.

Electrolytes play a critical role in almost every metabolic reaction in the body. For example, they:

Water is essential to life. Dehydration occurs when more water is lost from the body than is replaced. A loss of 20% of the body's water can be fatal. Water balance and electrolyte concentrations are closely intertwined. Dehydration is a major cause of electrolyte imbalances.

Electrolytes, proteins, nutrients, waste products, and gases are dissolved in fluid in the body. This fluid is not distributed evenly. About two-thirds of it is found inside cells (intracellular fluid). The rest is found in the spaces between cells (interstitial fluid), in the circulatory system, and in small amounts in other places such as the stomach. Changes in the concentration of electrolytes results in changes to the distribution of water throughout the body as water moves into or out of cells.

The components of body fluid—electrolytes, proteins, and so forth—are not evenly distributed either. Different types of cells have membranes that allow some electrolytes (and other components of the fluid) to pass across them while blocking others. This difference in the distribution of electrolytes (and thus electric charges) on either side of cell membranes makes it possible for many metabolic reactions to take place.

Water passes easily across cell membranes. When fluid with two different concentrations of electrolytes is separated by a cell membrane, there is pressure (called osmotic pressure) for water to flow across the membrane from fluid that contains fewer electrolytes (less concentrated) into fluid that contains more electrolytes (more concentrated). The cell uses energy to resist osmotic pressure and maintain different concentrations of electrolytes on either side of the membrane, because even small changes in the concentrations and distribution of electrolytes can result in large movements of water in and out of cells. Maintaining this difference, or gradient, across cell membranes is a major part of the complex regulatory events called homeostasis that keep conditions within the body stable within very narrow limits. When there is an imbalance in electrolytes many systems in the body are affected and serious, even fatal, health problems can result.

An electrolyte imbalance occurs when the concentration of a specific electrolyte is either too high or too low. The concentration of electrolytes is strongly affected by the amount of fluid in the body. Fluid balance is largely controlled by hormones that act on the kidneys and regulate how much urine the kidneys produce. The average male adult loses about 1.5–2.5 L of water daily through urine production, sweating, breathing out water vapor, and bowel movements, depending on exercise levels and environmental temperature. The United States Institute of Medicine recommends that adult men drink a minimum of 3 L of liquids a day, and that women drink a minimum of 2.2 L to replace lost water.

Dehydration is a major cause of electrolyte imbalance. It occurs whenever water is lost from the body and not replaced fairly quickly. When fluids are lost, electrolytes in those fluids are lost too, increasing the risk of electrolyte imbalance. Dehydration can be caused in many ways. These include:

Electrolyte imbalances can have other causes, unrelated to dehydration. These include:

Each electrolyte has a special function in the body, although if one electrolyte is out of balance, the concentrations and actions of other electrolytes are often affected. The serum concentration of sodium, potassium, and chloride can be measured in a simple blood test. Sodium, chloride, potassium, and calcium concentrations can also be determined from a urine sample. A urine test helps show how well the kidneys are functioning. Electrolyte imbalances are most common among the seriously ill and the elderly. Kidney (renal) failure is the most common cause of electrolyte imbalances.

Too low a concentration of sodium in the blood causes hyponatremia. This is one of the most common electrolyte imbalances, and occurs in about 1% of hospitalized individuals. It can result from vomiting, diarrhea, severe burns, taking certain drugs that cause the kidneys to selectively excrete sodium, inadequate salt intake, water intoxication (a problem among the elderly with dementia), hormonal imbalances, kidney failure, and liver damage. Symptoms include nausea, vomiting, headache, tissue swelling (edema), confusion, mental disorientation, hallucinations, muscle trembling, seizures, and coma.

POTASSIUM. Potassium ions play a major role in regulating fluid balance in cells, the transmission of nerve impulses, and in muscle contractions. Too high a concentration of potassium causes a condition called hyperkalemia that is potentially life threatening. The most common cause is kidney failure. It can also result from severe burns or injury (excess potassium released from injured cells), inadequate adrenal hormones (Addison's disease), the use of certain medications, and excessive use of potassium supplements. Sometimes hyperkalemia occurs in conjunction with hypernatremia. Symptoms include nausea, diarrhea, weakness, muscle pain, irregular heart beat, coma, and death.

Abnormally low concentrations of potassium cause hypokalemia. Hypokalemia can result from excess adrenal hormones (Cushing's disease), kidney disease, long-term use of certain diuretic drugs, laxative abuse, bulimia, and kidney failure. Symptoms include increased production of urine, muscle pain, paralysis, irregular heart beat, and low blood pressure.

CALCIUM. Calcium is needed to build and maintain bones. It also plays a role in nerve impulse transmission and muscle contraction. Excess calcium results in a condition called hypercalcemia. Hypercalcemia can be caused by too much parathyroid hormone (PTH), certain cancers, some genetic disorders, and excessive use of antacids containing calcium in rare cases. Symptoms include bone and muscle pain, mental changes such as depression and confusion, increased urine production, fatigue, nausea, and vomiting.

Abnormally low concentrations of calcium cause hypocalcemia. Hypocalcemia can be caused by too little parathyroid hormone, kidney failure, and vitamin D deficiency. Vitamin D is necessary for the body to absorb calcium. Symptoms include muscle twitches and spasms, convulsions, mental changes such as depression and irritability, dry skin, and brittle nails.

MAGNESIUM. Magnesium is involved in protein synthesis and cellular metabolism. Abnormally high concentrations of magnesium, or hypermagnesemia, may occur with severe (end-stage) renal failure or by overdose of magnesium-containing intravenous fluids. Hypermagnesemia is rare. Symptoms include exhaustion, low blood pressure, depressed heart and breathing rate, and slow reflexes.

Abnormally low concentrations of magnesium, or hypomagnesemia, are most common among people with alcoholism and those who are severely malnourished. Other causes include digestive disorders that interfere with the absorption of magnesium from the intestines. Symptoms of hypomagnesemia include vomiting, weight lose, leg cramps, muscle spasms, seizures, and irregular heartbeat.

CHLORIDE. Chloride is involved in regulating blood pressure. High concentrations of chloride, called hyperchloremia, can be caused by kidney failure, kidney dialysis, and an overproduction of parathyroid hormone. Symptoms include weakness, headache, nausea, and vomiting. In people with diabetes, hyperchloremia makes it difficult to control blood glucose levels.

Hypochloremia often occurs along with hyponatremia or hypokalemia and is caused by excessive fluid loss (e.g., diarrhea). Serious deficiencies of chloride cause the blood to become less acidic, resulting in a condition called metabolic alkalosis. Symptoms of severe hypochloremia include confusion, paralysis, and difficulty breathing.

PHOSPHATE. Phosphate helps control the acidity level (pH) of the blood. Phosphate also causes calcium to be deposited in bones. High blood levels of phosphate, or hyperphosphatemia, often result in too low levels of calcium, or hypocalcemia. Hyperphosphatemia is usually caused by kidney failure. It can also result from kidney dialysis, parathyroid gland dysfunction, and several inherited diseases. Mild hyperphosphatemia usually produces no symptoms. Severe imbalance can cause tingling in the fingers, muscle cramps, and convulsions.

Most people get all the electrolytes and water they need from a normal diet. However, some individuals, such as athletes, people with severe diarrhea and vomiting, cancer patients, people with hormonal imbalances, and other very ill people, need fluid and electrolyte replacement therapy. Short-term therapy often quickly restores electrolyte balances.

Electrolyte replacement supplements can be sold either over-the-counter or by prescription. Prescription supplements are used for seriously ill or hospitalized patients and can be given by mouth or intravenously under supervision of a physician.

In North America, commonly used over-the-counter electrolyte replacements include:

As with any dietary supplement, electrolyte replacements can be abused. When used properly, they are of great benefit and have no undesirable side effects.

Sports drinks should not be given to children who need rehydration because of vomiting and diarrhea. Instead, oral rehydration liquids specially formulated for children should be used.

The goal of electrolyte replacement therapy is to restore the body to its natural condition. When used this way, electrolyte replacement does not interfere with other drugs. Many drugs, however, have the potential to cause electrolyte imbalances. When starting a new drug, individuals should discuss possible side effects with their healthcare provider.

No complications are expected when electrolyte replacement therapy is used as directed. Seriously ill individuals and those using long-term electrolyte replacement therapy should have electrolyte levels checked regularly.

Dehydration is a real threat to children, especially infants and toddlers. Parents should be alert to dehydration caused by illness or athletic activity and begin oral fluid and electrolyte replacement therapy immediately. Parents of young children with vomiting, diarrhea, or high fever should consult their healthcare provider promptly about steps to take to prevent dehydration.

See also Binge eating ; Dehydration ; Diarrhea diet ; Giardiasis ; Hydration ; Low-sodium diet ; Magnesium ; Sodium ; Sports nutrition .