Sodium, an element of the periodic table, is a soft metal. The sodium that the body uses, however, isn't in its elemental or metallic form. Instead, it's been chemically reacted into the form of salt, often NaCl, or table salt. The body uses sodium for many different things.
Significance
Sodium is critically important to body function, but is actually quite difficult to find in nature. Ancient civilizations that lived near the ocean had access to sodium through dried seawater, and some cultures found salt mines nearby, but in many human civilizations until recent centuries, sodium was difficult to come by. As a result, humans evolved a strong desire for the taste of salt, which is why salt tastes good on food.
Function
There are many functions of sodium in the body. It helps to maintain fluid balance, and as such, the kidneys actively pull sodium out of forming urine to maintain it in the bloodstream. Sodium also helps establish what's called the "resting membrane potential," explains Lauralee Sherwood, Ph.D., in her book "Human Physiology." This resting membrane potential allows cells to receive information about their environments and to communicate with one another.
Considerations
It's possible to lose large amounts of sodium when you sweat. For most people, this isn't a problem -- there's plenty of sodium in the average US diet and it's easy to replenish what's lost. Athletes can sometimes lose so much sodium in sweat, however, that they begin to have problems with fluid balance, explains Sherwood. For this reason, salt-containing rehydration drinks help prevent symptoms.
Expert Insight
Sodium is actually the chemical responsible for the function of nerve cells, notes Gary Thibodeau, Ph.D., in his book "Anatomy and Physiology." Nerve cells pump sodium from the inside of the cell to the outside, segregating it in the fluid around the cell. When a nerve cell sends a chemical signal, it allows the sodium from the surrounding fluid to enter the cell. This produces an electrical impulse that travels down the nerve cell.
Misconceptions
Though sodium used to be hard for humans to obtain in diet, and though it's important to normal body function, it's not lacking from the average U.S. diet. As a result, there's no reason to supplement with extra sodium. In fact, extra sodium causes harm--it can increase blood pressure and result in cardiovascular, tissue, and organ damage, explains Thibodeau. Despite the fact that a healthy body depends upon a certain amount of sodium, more is definitely not better.
References
- "Human Anatomy"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
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