An essential mineral that our bodies regulate and conserve. Excess sodium retention increases the fluid volume (edema) and low sodium leads to less fluid and relative dehydration. The adult body averages a total content of over 100 grams of sodium, of which a surprising one-third is in bone. A small amount of sodium does get into cell interiors, but this represents only about ten percent of the body content. The remaining 57 percent or so of the body sodium content is in the fluid immediately surrounding the cells, where it is the major cation (positive ion). The role of sodium in the extracellular fluid is maintaining osmotic equilibrium (the proper difference in ions dissolved in the fluids inside and outside the cell) and extracellular fluid volume. Sodium is also involved in nerve impulse transmission, muscle tone and nutrient transport. All of these functions are interrelated with potassium.