Sodium (and chloride) deficiency does not generally result from inadequate dietary intake, even in those on very low-salt diets (5).
Low blood serum sodium concentration (less than 136 mmol/liter) may result from increased fluid retention ('dilutional hyponatremia'), due to inappropriate anti-diuretic hormone (ADH) secretion or excessive water intake.
In addition, increased sodium loss caused by severe or prolonged vomiting or diarrhea, excessive and persistent sweating, the use of some diuretics, and some forms of kidney disease, can lead to dilutional hyponatremia.
Hyponatremia has been recognized as a potential problem in individuals competing in very long endurance exercise events, such as marathons (56). Participants who developed hyponatremia during such exercise events had evidence of fluid overload despite relatively modest fluid intakes, suggesting that fluid excretion was inadequate and/or the fluid needs of these long-distance athletes may be less than currently recommended (57). It has been speculated that the use of non-steroidal anti-inflammatory drugs (NSAIDs) may increase the risk of exercise-related hyponatremia by impairing water excretion (58).
Symptoms of low blood serum sodium concentrations (hyponatremia) include headache, nausea, vomiting, muscle cramps, fatigue, disorientation, and fainting.
Complications of severe and rapidly developing hyponatremia may include swelling of the brain ('cerebral edema'), seizures, coma, and brain damage.
Acute or severe hyponatremia may be fatal without prompt and appropriate medical treatment (59).
Authored by Dr Peter Engel in 2010, reviewed and revised by Dr. Volker Elste on 20.09.2017.