What is Sodium deficiency?

Hyponatremia (American English) or hyponatraemia (British English) is low sodium concentration in the blood. Normal serum sodium levels are between approximately 135 and 145 mEq/liter (135 - 145 mmol/L). Hyponatremia is generally defined as a serum sodium level of less than 135 mEq/L and is considered severe when the serum sodium level is below 125 mEq/L.

Too little sodium in the diet alone is very rarely the cause of hyponatremia, although it can promote hyponatremia indirectly and has been associated with MDMA-induced hyponatremia. Sodium loss can lead to a state of low blood volume, which signals the release of anti-diuretic hormone (ADH). ADH release leads to water retention and dilution of the blood resulting in a low sodium concentration.

Many conditions including congestive heart failure, liver failure, kidney failure and pneumonia are commonly associated with a low sodium concentration in the blood. This state can also be caused by overhydration from drinking too much water because of excess thirst (polydipsia). Exercise-associated hyponatremia (EAH) is common in marathon runners and participants of other endurance events. 13% of the athletes who finished the 2002 Boston Marathon were in a hyponatremic state, that is, the salt levels in their blood had fallen below usual levels.

Sodium is the primary positively charged ion in the environment outside of the cell and cannot freely cross from the interstitial space into the cell. Charged sodium ions attract up to 25 water molecules around them thereby creating a large polar structure that is too large to pass through the cell membrane.