The normal concentration of sodium in the blood plasma is 136-145 mM. If the sodium level falls too late, it's called hyponatremia; if it gets too high, it's called hypernatremia.

A sodium level in the blood that is too low is dangerous and can cause seizures and coma. Very high sodium levels can lead to seizures and death.

Sodium is a mineral element and an important part of the human body. It controls the volume of fluid in the body and helps maintain the acid-base level. About 40% of the body's sodium is contained in bone, some is found within organs and cells and the remaining 55% is in blood plasma and other fluids outside cells. Sodium is important in proper nerve conduction, the passage of various nutrients into cells, and the maintenance of blood pressure.

The body continually regulates its handling of sodium. When a person eats...