Sodium is often associated with high blood pressure and several expert resources, including the National Institutes of Health and the Centers for Disease Control and Prevention, recommend consuming no more than 2,300mg per day. Individuals over age 51, African Americans and individuals with hypertension, diabetes or kidney disease are encouraged to consume no more than 1,500mg per day. The body does need some sodium, however, and it actually plays a crucial role in maintaining healthy blood pressure levels.
Sodium in the Body
Sodium is an electrolyte and helps conduct the nerve signals responsible for muscle contractions. Sodium is also responsible for keeping your body fluids in balance. Your body stores sodium in the blood and in the fluid surrounding the cells, and you get most of your sodium from your diet. Your kidneys control the sodium levels in your body by clearing excess sodium through urination. Sodium affects blood pressure by changing the volume of fluid in your body and by affecting kidney function.
Sodium and Fluid Volume
Normal blood sodium levels range between 135 to 145 milliequivalents per liter, or mEg/L. At that level, the volume of water in your blood is in balance and your blood pressure remains in the normal range. If sodium levels rise, your body has to put more fluid in the blood to dilute the sodium, which increases blood volume. The increased fluid volume in the blood vessels has a similar effect to running water through a hose--the higher the volume of water is, the greater the amount of pressure in the hose is. When sodium levels drop, the blood needs less fluid and the pressure decreases.
Sodium and Kidney Function
The kidneys have millions of tiny structures called glomeruli that filter wastes and excess sodium out of the blood. The glomeruli also remove excess fluid to help maintain a healthy blood volume. If you continually have high blood sodium, the glomeruli have to work harder to filter out the excess sodium. Over time, this causes damage to the glomeruli and they don't work as efficiently. The loss of efficiency results in fluid imbalances, which can lead to high blood pressure and kidney damage. The kidneys may also filter too much sodium out of the blood, leading to excess urination and sodium deficiencies.
Maintaining Fluid Balance
Fluid intake, such as from drinking water, also affects the fluid and sodium levels in your body. When you are properly hydrated, your fluid levels remain in the healthy range. When you are not, your blood becomes more concentrated, your sodium levels rise and your body has to pull fluid from the tissues to dilute the sodium. Illnesses, such as diarrhea, and excessive sweating can also negatively affect the fluid balance in your body. By keeping your sodium intake within the healthy range for your age and health status, and drinking plenty of water, you contribute to maintaining a healthy blood pressure and healthy kidney function. Water needs vary by individual, but in general, pale yellow urine indicates that you are properly hydrated.
References
- MedlinePlus; Sodium in diet; David Zieve, MD, MHA; May 2010
- Centers for Disease Control and Prevention; Most Americans Should Consume Less Sodium (1,500 mg/day or less); Feb. 2011
- MedlinePlus; Sodium -- blood; David C. Dugdale, III, MD; Nov. 2009
- The Merck Manual of Medical Information; Water Balance; ames L. Lewis, III, MD; August 2008
- Merck Manuals Online Medical Library; Sodium; Larry E. Johnson, MD, PhD; August 2008
