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Causes
By Mayo Clinic staffSodium plays a key role in your body. It helps maintain normal blood pressure, supports the work of your nerves and muscles, and regulates your body's fluid balance.
When the sodium levels in your blood become too low, excess water enters your cells and causes them to swell. Swelling in your brain is especially dangerous because the brain is confined by your skull and unable to expand.
Types of hyponatremia
Normal blood plasma contains between 136 and 145 milliequivalents per liter (mEq/L) of sodium. Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L.
The imbalance between sodium and water in your blood may occur in three primary ways:
- In hypervolemic hyponatremia, excess water dilutes the sodium concentration, causing low sodium levels. Hypervolemic hyponatremia is commonly the result of kidney failure, heart failure or liver failure.
- In euvolemic hyponatremia, normal water levels are combined with low sodium levels. This condition is commonly due to chronic health conditions, cancer or certain medications.
- In hypovolemic hyponatremia, your water and sodium levels are both low. This may occur, for example, when exercising in the heat without replenishing your fluid electrolytes or with marked blood loss.
Causes of hyponatremia
Many possible conditions and lifestyle factors can lead to hyponatremia, including:
- Consuming excessive water during exercise (exertional hyponatremia). Because you lose sodium through sweat, drinking too much water during endurance activities, such as marathons and triathlons, can dilute the sodium content of your blood.
- Hormonal changes due to adrenal gland insufficiency (Addison's disease). Your adrenal glands produce hormones that help maintain your body's balance of sodium, potassium and water.
- Hormonal changes due to an underactive thyroid (hypothyroidism). Hypothyroidism may result in a low blood-sodium level.
- Water pills (diuretics) — especially thiazide diuretics. Diuretics work by making your body excrete more sodium in urine.
- Syndrome of inappropriate anti-diuretic hormone (SIADH). In this condition, high levels of the anti-diuretic hormone (ADH) are produced, causing your body to retain water instead of excreting it in your urine.
- Primary polydipsia. In this condition, your thirst increases significantly, causing you to drink excessive amounts of fluid.
- Certain medications. Some medications, such as some antidepressants and pain medications, can cause you to urinate or perspire more than normal.
- The recreational drug Ecstasy. This amphetamine causes a ripple effect on the body's ADH and water levels that — especially when combined with heavy drinking — increases the risk of severe and even fatal cases of hyponatremia.
- Chronic, severe vomiting or diarrhea. This causes your body to lose fluids and electrolytes, such as sodium.
- Dehydration. In dehydration, your body loses fluids and electrolytes.
- Diet. A low-sodium, high-water diet can disturb the proper balance between sodium and fluids in your blood. Excessive intake of diuretics, including beer, can have the same effect.
- Cirrhosis. Liver disease can cause fluids to accumulate in your body.
- Kidney problems. Kidney failure and other kidney disease may render your body unable to efficiently remove excess fluids from your body.
- Congestive heart failure. This condition causes your abdomen and lower extremities to retain fluids.
- Rose BD. Diagnosis of hyponatremia. http://www.uptodate.com/home/index.html. Accessed May 26, 2009.
- Gibbs MA, et al. Electrolyte disturbances. In: Marx JA, et al., eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 6th ed. St. Louis, Mo.: Mosby; 2006. http://www.mdconsult.com/das/book/body/139569939-5/845288330/1365/382.html#4-u1.0-B0-323-02845-4..50128-1_6348. Accessed May 26, 2009.
- Rose BD. Causes of hyponatremia. http://www.uptodate.com/home/index.html. Accessed May 26, 2009.
- Rose BD. Treatment of hyponatremia. http://www.uptodate.com/home/index.html. Accessed May 26, 2009.
- Weinberg MS, et al. Disorders of sodium homeostasis. In: Ferri FF. Practical Guide to the Care of the Medical Patient. 7th ed. St. Louis, Mo.: Mosby; 2007. http://www.mdconsult.com/das/book/body/139569939-3/0/1417/921.html?tocnode=52510185&fromURL=921.html. Accessed May 26, 2009.
- Drezner JA, et al. Environmental influences. In: Rakel RE. Textbook of Family Medicine. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/139569939-6/845288600/1481/481.html#4-u1.0-B978-1-4160-2467-5..50043-9--cesec21_2481. Accessed May 26, 2009.
- Ferrante MA, et al. Endogenous metabolic disorders. In: Goetz GD. Textbook of Clinical Neurology. 3rd ed. Philadelphia, Pa.: W.B. Saunders; 2007. http://www.mdconsult.com/das/book/body/139569939-7/845289096/1488/324.html#4-u1.0-B978-1-4160-3618-0..10038-4_2905. Accessed May 26, 2009.
- Campbell GA. The agony of ecstasy: MDMA (3,4-methylenedioxymethamphetamine) and the kidney. Clinical Journal of the American Society of Nephrology. 2008;3:1852.
