More than half of a person's body weight is water. Doctors think about water in the body as being restricted to various spaces, called fluid compartments. The three main compartments are
Fluid within cells
Fluid in the space around cells
Blood
To function normally, the body must keep fluid levels from varying too much in these areas.
Some minerals—especially the macrominerals (minerals the body needs in relatively large amounts)—are important as electrolytes. Electrolytes are minerals that carry an electric charge when they are dissolved in a liquid, such as blood. The blood electrolytes—sodium, potassium, chloride, and bicarbonate—help regulate nerve and muscle function and maintain acid-base balance and water balance, which have to be maintained in a normal range for the body to function.
Electrolytes, particularly sodium, help the body maintain normal fluid levels in the fluid compartments because the amount of fluid a compartment contains depends on the amount (concentration) of electrolytes in it. If the electrolyte concentration is high, fluid moves into that compartment (a process called osmosis). Likewise, if the electrolyte concentration is low, fluid moves out of that compartment. To adjust fluid levels, the body can actively move electrolytes in or out of cells. Thus, having electrolytes in the right concentrations (called electrolyte balance) is important in maintaining fluid balance among the compartments.
The kidneys help maintain electrolyte concentrations by filtering electrolytes and water from blood, returning some to the blood, and excreting any excess into the urine. Thus, the kidneys help maintain a balance between the electrolytes a person takes in every day by consuming food and beverages and the electrolytes and water that pass out of the body in the urine (are excreted).
If the balance of electrolytes is disturbed, a person can develop health issues. For example, an electrolyte imbalance can result from the following:
Becoming dehydrated or overhydrated
Taking certain medications
Having certain heart, kidney, or liver disorders
Being given intravenous fluids or feedings in inappropriate amounts
