The condition of having too little sodium in the body is called
"hyponatremia" (literally, low-sodium). Since sodium is necessary for
proper nerve and muscle activity, as well as for water balance in the
body, symptoms of hyponatremia include loss of neural function
(confusion, lethargy) and of muscle function (twitchyness), and can
lead to coma and death. Sodium deficiency most commonly affects
athletes (who tend to excercise hard, sweat a lot, and not replace
electrolytes as they're used up) and the elderly.
Penn State A to Z Health Topics: Hyponatremia
Because the brain is very sensitive to sodium levels, low sodium
causes symptoms including confusion and lethargy. The patient may feel
nauseated, and experience muscle twitching, which can progress to
seizures. Eventually, severe hyponatremia can lead to coma and death.
Mayo Clinic: Low Blood Sodium in Older Adults
Mayo Clinic: Low Blood Sodium in Athletes
Oregon State University: Sodium
"It is possible to have a sodium deficiency resulting in symptoms such
as severe muscle cramps, extreme weakness, and nausea. This is most
likely to occur in people who are exercising hard and long in hot,
humid weather. It can also happen as a result of severe or prolonged
vomiting or diarrhea."
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