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Overview of Sodium's Role in the Body

By

James L. Lewis III

, MD, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

Reviewed/Revised Sep 2023
VIEW PROFESSIONAL VERSION

Most of the body’s sodium is located in the blood and in the fluid around cells. Sodium helps the body keep fluids in a normal balance (see About Body Water About Body Water Water accounts for about one half to two thirds of an average person’s weight. Fat tissue has a lower percentage of water than lean tissue and women tend to have more fat, so the percentage... read more ). Sodium plays a key role in normal nerve and muscle function.

Sodium enters the body through food and drink and leaves the body primarily in sweat and urine. Healthy kidneys maintain a consistent level of sodium in the body by adjusting the amount excreted in the urine. When sodium consumption and loss are not in balance, the total amount of sodium in the body is affected. The amount (concentration) of sodium in the blood may be

Controlling blood volume

The total amount of sodium in the body affects the amount of fluid in blood (blood volume) and around cells. The body continually monitors blood volume and sodium concentration.

When either becomes too high, sensors in the heart, blood vessels, and kidneys detect the increases and stimulate the kidneys to increase sodium excretion, thus returning blood volume to normal.

When blood volume or sodium concentration becomes too low, the sensors trigger mechanisms to increase blood volume. These mechanisms include the following:

Maintaining fluid and sodium balance in older adults

As people age, the body is less able to maintain fluid and sodium balance for several reasons:

A low sodium level in blood (hyponatremia Hyponatremia (Low Level of Sodium in the Blood) In hyponatremia, the level of sodium in blood is too low. A low sodium level has many causes, including consumption of too many fluids, kidney failure, heart failure, cirrhosis, and use of diuretics... read more ) is more common among older adults. Hyponatremia usually results when the body retains too much fluid, as occurs in heart failure or liver disease. Hyponatremia also occurs in older adults who take certain types of diuretics (thiazide diuretics such as hydrochlorothiazide), particularly if the kidneys are not functioning normally. Diuretics, which are sometimes called water pills, are medications that help the body eliminate excess fluid. Using liquid nutritional supplements or receiving intravenous fluids that are low in sodium while in the hospital also may cause hyponatremia in older adults.

NOTE: This is the Consumer Version. DOCTORS: VIEW PROFESSIONAL VERSION
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