Bioavailability
Absorption is greater than 90%.
Interactions
Interactions are listed in the footnote.
36
Function
Sodium (Na
+) and chloride (Cl
- ) are the principal electrolytes in
the fluid outside of cells (extracellular fluid), which includes blood plasma.
Sodium and chloride serve to maintain fluid levels, muscle
function, and support the blood and lymphatic systems. Membrane Potential
Sodium and chloride contribute to the charge differences across
cell membranes.
Potassium concentrations are about 30 times higher inside than
outside cells; sodium concentrations are more than 10 times higher outside than inside cells.
36 Interactions Nutrient Diets emphasizing fruits, vegetables, whole grains, poultry, fish, nuts, and low-fat dairy products lower
blood pressure compared to typical US diets. Potass
ium and calcium intakes are higher with such diets.
The combination of such diets and reduced salt intake
lowers blood pressure more than either intervention
alone.
Drug The following drug families and drugs increase the risk of hyponatremia (low blood sodium concentration): Carbamazepine
.
Chlorpropamide
.
Clofibrate
.
Cyclophosphamide
.
Desmopressin
.
(Continued)
Diuretics
, including hydrochlorthiazide, furosemide (Lasix).
Non-steroidal anti-inflammatory drugs (NSAIDs)
, including ibuprofen (Advil, Motrin), naproxen (Aleve).
Opiates
, including codeine and morphine.
Oxytocin
(Pitocin).
Phenothiazines
, including prochlorperazine (Compazine) and promethazine (Phenergan).
Serotonin-reuptake inhibitors (SSRIs)
, including fluoxetine (Prozac)
and paroxetine (Paxil).
Tricyclic antidepressants
, including amitriptyline (Elavil), and imipramine (Doornail).
Vincristine
(Oncoming).
These concentration differences across cell membranes create an
electrochemical gradient known as the membrane potential.
Membrane potential is maintained by ion pumps in the cell
membrane, especially the sodium- and potassium-ATPase pumps. Pump activity is estimated to account for 20% to 40% of the resting energy expenditure in a typical adult.
Cell membrane potential is critical for nerve impulse
transmission, muscle contraction, and heart function. Blood Volume and Blood Pressure
Sodium is the primary determinant of extracellular fluid volume,
including blood volume.
Mechanisms that regulate blood volume and blood pressure
work, in part, by adjusting the body’s sodium content.
In general, sodium retention
results in water retention and
sodium loss results in water loss. Digestion
Chloride, in the form of hydrochloric acid (HCl), is an important
component of gastric juice, which aids the digestion and absorption of nutrients. Nutrient Absorption and Transport
Sodium absorption in the small intestine plays a role in the
absorption of chloride, amino acids, glucose, and water.
Similar mechanisms reabsorb these nutrients after they are
filtered from the blood by the kidneys.
Deficiency (Hyponatremia)
Hyponatremia, a low blood sodium concentration, results from
increased sodium loss or increased fluid retention.
Conditions that increase the loss of sodium and chloride include
large sweat losses, severe or prolonged vomiting or diarrhea, the use of some diuretics, and some forms of kidney disease.
Nutrition for Sports, Essentials of 164
