How does sodium help maintain water and ion balance in the human body?

Sodium is essential for maintaining fluid and ion balance in the human body through several key mechanisms:

Extracellular Regulation and Water Balance

Sodium is the primary extracellular ion and plays a critical role in holding water within body tissues. By working alongside chlorine and bicarbonate, it helps maintain the balance of positive and negative ions in body fluids and tissues. Because of this relationship, a low salt intake can lead to water loss, while excess sodium may cause edema, or water retention. The hormone aldosterone is responsible for controlling this balance of sodium and water.12

Cellular Ion Balance

At the cellular level, the sodium-potassium pump maintains a specific concentration gradient across the cell membrane. This protein uses metabolic energy to actively transport sodium ions out of the cell while pumping potassium ions in. This steady-state difference is vital for the resting potential of cells and various bioelectric phenomena, such as the action potential.23