Causes

Sodium 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.

A normal blood sodium level is between 135 and 145 milliequivalents per liter (mEq/L). Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L.

Many possible conditions and lifestyle factors can lead to hyponatremia, including:

• Certain medications. Some medications, such as some water pills (diuretics), antidepressants and pain medications, can interfere with the normal hormonal and kidney processes that keep sodium concentrations within the healthy normal range.
• Heart, kidney and liver problems. Congestive heart failure and certain diseases affecting the kidneys or liver can cause fluids to accumulate in your body, which dilutes the sodium in your body, lowering the overall level.
• 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 normally in your urine.
• Chronic, severe vomiting or diarrhea and other causes of dehydration. This causes your body to lose electrolytes, such as sodium, and also increases ADH levels.
• Drinking too much water. Drinking excessive amounts of water can cause low sodium by overwhelming the kidneys' ability to excrete water. Because you lose sodium through sweat, drinking too much water during endurance activities, such as marathons and triathlons, can also dilute the sodium content of your blood.
• Hormonal changes. Adrenal gland insufficiency (Addison's disease) affects your adrenal glands' ability to produce hormones that help maintain your body's balance of sodium, potassium and water. Low levels of thyroid hormone also can cause a low blood-sodium level.
• The recreational drug Ecstasy. This amphetamine increases the risk of severe and even fatal cases of hyponatremia.