Why is sodium important for human survival?

Sodium is a mineral essential to human survival -- so much so that the word "salary" comes from the Latin for salt. Without enough sodium in your body, your cellular function and neural communication shut down. Essential as sodium is, though, you don't need to supplement with it under ordinary conditions.

Sodium
Most of the sodium you get in your diet is in the form of sodium chloride, a salt compound. Sodium itself is an element -- more specifically, it's a metal -- but it's quite rare in elemental form, because it's so reactive.

In nature, sodium occurs in the form of any number of salts. A sodium salt consists of positively charged particles of sodium combined with negatively charged particles of various identities. Sodium chloride aside, other common sodium salts include sodium bicarbonate -- baking soda -- and sodium hydroxide, which is lye.

Sodium and Cells
Sodium is essential to cellular function for many reasons. It's critical to absorbing certain nutrients from the digestive tract -- glucose, for instance -- and also allows some molecules that couldn't otherwise pass through the cell membrane to cross.

It's also one of the chemicals that helps establish the resting membrane potential. This produces a negative charge inside cells relative to the fluid surrounding them, which allows for transport of molecules and cellular communication, explains Dr. Gary Thibodeau in his book "Anatomy and Physiology."

Other Functions
Sodium is also critical to the function of the nervous system and to muscular contraction; nerves send signals conducted through movement of positively charged sodium particles.

Furthermore, sodium helps maintain fluid balance in the body. As your kidneys filter blood, explains Dr. Lauralee Sherwood in her book "Human Physiology," they actively resorb sodium into the bloodstream, which helps pull water back into the bloodstream along with it. This helps you hang on to as much water as possible.

Considerations
Generally speaking, critical as sodium is to health, you don't need to supplement with it. This is because you likely get plenty in your diet. Most people actually get too much sodium. One population occasionally benefits from sodium supplementation: elite athletes. These individuals sweat so much -- sweat contains sodium -- that they can lose much of their sodium over the course of an event, and can suffer health effects if they don't supplement.