Definition of Hyponatremia
Hyponatremia: An abnormally low concentration of
sodium in the blood. Too little sodium can cause cells to
malfunction, and extremely low sodium can be fatal. Hyponatremia has many causes including medications such as diuretics and antidepressants, hypothyroidism, cortisone deficiency (such as in Addison's disease), dehydration, vomiting or diarrhea, severe burns, kidney or heart failure, and cirrhosis.
The symptoms of hyponatremia include bloating and puffiness in the
face and fingers, nausea, vomiting, muscle weakness, headache and
disorientation.
Hyponatremia has increasingly become a problem in high-endurance
events such as marathons, ultramarathons, hiking and long military
marches. Athletes need to drink regularly, for example during a long
race, to prevent dehydration, but excess water can lead to
hyponatremia.
Women appear more prone to hyponatremia than men. About
half the women studied who finished the New Zealand Ironman triathlon
developed hyponatremia, compared with 14 percent of the men,
according to a report in the journal Medicine and Science in Sports
and Exercise.
Hyponatremia can be prevented in high-endurance
activities. A racer can calculate their "sweat rate" ahead of a race
by weighing before and after exercising for half an hour
at the pace and under the conditions anticipated in the race. For
every pound lost through sweating, the racer should drink a pint per
hour during the race. (or in metric terms, for every kilo lost, the
racer should drink about a liter per hour during the race.) A sports
beverage (e.g. Gatorade) that contains carbohydrates and
electrolytes, may help prolong an athlete's peak performance and
replace sodium lost in sweat. Athletes should also salt their food
for several days before a high-endurance event.
Sodium is the major positively charged ion (cation) in the fluid
outside of cells of the body. The chemical notation for sodium is Na.
When combined with chloride, the resulting substance is table salt.
The normal blood sodium level is 135 - 145 milliEquivalents/liter
(mEq/L), or in international units, 135 - 145 millimoles/liter
(mmol/L).
Last Editorial Review: 5/22/2004Common Misspellings: hyponaturemia
- Electrolytes - Read about blood electrolytes (sodium, potassium, chloride, and bicorbonate) and the effects of electrolyte imbalances like kidney failure, low blood pressure, hypokalemia, and hyperkalemia.
- Kidney Failure - Learn about kidney failure, in which the body has fluid retention, risen blood pressure, toxin build up and lack of red blood cells. Symptoms include fatigue, nausea, and apetite loss.
- Urinalysis - Learn about the urinalysis test. Diseases and conditions such as urinary tract or kidney infection, kidney stones, kidney failure, diabetes, or high blood pressure can be diagnosed or monitored.
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