Sodium is a mineral. In the body, it carries an electrical charge -- and a charged mineral is called an electrolyte. The body regulates the level of sodium in the body through numerous interacting processes because the concentration must remain in a narrow range. If sodium levels deviate too high or too low, it causes problems in the body. Sodium is important for fluid distribution, blood pressure, cellular work and electrical activity.
Sodium atoms carry a strong positive electrical charge. They dissolve in the body fluids, which are mostly water. Water does not carry a charge, but it is a polar molecule. This means that it has a positive and a negative side. Water follows sodium in the body. If the concentration of sodium increases in a tissue, the fluid there increases as well. In this way, concentrations of sodium control the distribution of fluids in the body. This is important for ensuring that cells and tissues do not swell or shrink.
In addition to effects on the size of cells, the concentration of sodium helps determine the distribution of fluids in tissue spaces such as the blood vessels. Higher sodium intake leads to the retention of more water including water in the blood vessels. This raises the blood pressure. If it raises the blood pressure too high, this can cause health problems.
Sodium also helps transport other minerals and substances into, and out of, cells. Since the concentration of sodium outside the cells is higher than sodium inside the cells, sodium flows into cells when special protein channels open on the surface of the cell. This force is harnessed to bring other substances into, or out of, the cell.
The flow of sodium and potassium inside and outside cells creates an electrical gradient. This electrical activity is important for performing work and communication, especially for nerve and muscle tissue. For example, nerves use the flow of electrolytes to send signals, the beating of the heart is coordinated by the flow of electrolytes, and muscles use it to signal for contraction.