Athletes and trainers know that the body loses salt through sweat and that it's important to replace it. That's why many athletes drink sports drinks that contain salts before, during and after exercise to minimize things like muscle cramps that are associated with salt imbalance.
But salts are important not only for athletes. The human body needs various kinds of salts to be healthy and to function normally, and it has to maintain them at certain levels in different body compartments. Serious salt imbalances, like those that occur with dehydration, may lead to heart and nervous system problems that, unless they are rapidly resolved, can result in a medical emergency.
The foods we eat and fluids we drink contain mineral salts, which form electrolytes when they dissolve in the fluids in our bodies. They're present in blood, urine, in the fluid inside the body's cells and in the fluid in the space surrounding the cells. Sodium, calcium, chloride, magnesium and potassium are the most common electrolytes in the human body. They're essential for many heart, nerve and muscle functions. They also play an important role in keeping fluid levels normal in different body compartments.
As you might guess from their name, electrolytes are electrically charged, which means that they can conduct electrical impulses. The body needs electrical impulses to make muscle cells contract. The generation of an electrical impulse by a cell requires an electrical voltage to be maintained across the membrane of that cell. The difference in electrolyte levels creates and maintains these electrical voltages.
The levels of electrolytes in the body's fluid compartments are controlled by the movement of electrolytes into or out of those compartments. The kidneys filter electrolytes from the blood and work to keep their levels in the blood constant. Hormones (like antidiuretic hormone, aldosterone and parathyroid hormone) also help regulate electrolyte balance.
The body has to perform delicate balancing acts to keep water and electrolyte levels just right. For example, whenever the sodium level dips too low, the kidneys are stimulated to produce more urine, which restores the balance by lowering the amount of water in the blood. And when the sodium level gets too high, thirst develops, stimulating the person to drink. A hormone is also secreted by the brain in response to thirst that causes the kidneys to produce less urine. Together, these effects result in dilution of the sodium and the restoration of balance.
Learn about electrolyte imbalances on the next page.
The most common electrolyte imbalances are in sodium and potassium. Electrolyte imbalances are referred to with the prefixes "hypo" (low) and "hyper" (high), combined with the scientific name of the electrolyte.
- Hyponatremia (low sodium), the most common electrolyte imbalance, is a symptom of kidney disease. It can be caused by other disorders, some medications or when a person drinks too much water without consuming enough salt -- especially during hot weather, when more sweating occurs. The first symptoms are headache, fatigue, weakness and nausea. More severe cases can result in confusion, seizure, coma and death. Low sodium is treated by giving sodium and water intravenously.
- Hypernatremia (high sodium) can be caused by excessive fluid loss, diabetes, diarrhea, excessive vomiting and some medications. Thirst is typically the first symptom, and many of the other symptoms are the same as low sodium. Older hospitalized patients are particularly susceptible to hypernatremia. Treatment involves slowly replenishing water loss, usually over 48 hours, through drinking or intravenous administration.
- Hypokalemia (low potassium) is most commonly caused by some diuretics, medicines that help rid the body of excess sodium and water. Other causes include diarrhea, dietary deficiency and excessive sweating. Symptoms include irregular heartbeat, muscle pain, general discomfort or irritability, weakness and paralysis. Treatment can include potassium supplements, foods rich in potassium, or intravenous potassium and water. People who experience hypokalemia because of a diuretic may be given another type of diuretic that doesn't have potassium loss as a side effect.
- Hyperkalemia (high potassium) is much more serious than hypokalemia. It's usually caused by kidney failure or medications that reduce the amount of potassium excreted by the kidneys. High potassium can cause dangerous changes in the heart's function -- it can even cause the heart to stop. Other symptoms include tingling in the extremities, weakness and numbness. Treatment includes drugs that cause the body to eliminate potassium. In the case of severe or worsening hyperkalemia, treatment must be started immediately.
To learn more about electrolytes and keeping them in balance, follow the links on the next page.
Related HowStuffWorks Articles
- How Your Heart Works
- How Your Lungs Work
- How Your Kidneys Work
- How Blood Works
- How Ultrafiltration Works
- How Vasodilator Drugs Work
- How Fluid Overload and Edema Work
- How Orthopnea Works
- How Jugular Venous Distension Works
- How Heart Failure Affects Quality of Life
- How Inotropic Drugs Work
- How Diuretics Work
- How Low-Sodium Diets Work
More Great Links
- Alfonzo AV, Isles C, Geddes C, et al. Potassium disorders--clinical spectrum and emergency management. Resuscitation. 2006;70:10-25.
- Humphreys M. Potassium disturbances and associated electrocardiogram changes. Emerg Nurse. 2007;15:28-34.
- Hussain SM, Sureshkumar KK, Marcus RJ. Recent advances in the treatment of hyponatremia. Expert Opin Pharmacother. 2007;8:2729-2741.
- Lien YH, Shapiro JI. Hyponatremia: clinical diagnosis and management. Am J Med. 2007;120:653-658.
- Lin SH, Halperin ML. Hypokalemia: a practical approach to diagnosis and its genetic basis. Curr Med Chem. 2007;14:1551-1565.
- Parham WA, Mehdirad AA, Biermann KM. Hyperkalemia revisited. Tex Heart Inst J. 2006;33:40-47.
- Reynolds RM, Padfield PL, Seckl JR. Disorders of sodium balance. BMJ. 2006;332:702-705.
- Ruth JL, Wassner SJ. Body composition: salt and water. Pediatr Rev. 2006;27:181-187.
- Sedlacek M, Schoolwerth AC, Remillard BD. Electrolyte disturbances in the intensive care unit. Semin Dial. 2006;19:496-501.