Sodium is a mineral with the chemical symbol Na (Latin: natrium).

Sodium is present in great quantities in the earth's oceans as sodium chloride (common salt). It is also a component of many minerals, and it is an essential element for animal life. As such, it is classified as a “dietary inorganic macro-mineral.”

Sodium ions (often referred to as just "sodium") are necessary for regulation of blood and body fluids, transmission of nerve impulses, heart activity, and certain metabolic functions.

The human requirement for sodium in the diet is believed to be about 500 mg per day, which is typically less than a tenth as much as many diets "seasoned to taste."  Most people consume far more sodium than is healthy, and for people with salt-sensitive blood pressure, this extra intake may cause a negative effect on health.

References

Implementing recommendations for dietary salt reduction: Where are we?. DIANE Publishing. ISBN 1428929096.