Hyponatremia is a condition that occurs when the level of sodium in your blood is abnormally low. Sodium is an electrolyte, and it helps regulate the amount of water that’s in and around your cells.
In hyponatremia, one or more factors — ranging from an underlying medical condition to drinking too much water during endurance sports — causes the sodium in your body to become diluted. When this happens, your body’s water levels rise, and your cells begin to swell. This swelling can cause many health problems, from mild to life-threatening.
Hyponatremia treatment is aimed at resolving the underlying condition. Depending on the cause of hyponatremia, you may simply need to cut back on how much you drink. In other cases of hyponatremia, you may need intravenous fluids and medications.
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 sodium level is between 135 and 145 milliequivalents per liter (mEq/L) of sodium. 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 cause you to urinate or perspire more than normal.
- 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. This causes your body to lose fluids and electrolytes, such as sodium.
- Drinking too much water. 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. Drinking too much water at other times can also cause low sodium.
- Dehydration. Taking in too little fluid can also be a problem. If you get dehydrated, your body loses fluids and electrolytes.
- 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.
Hyponatremia signs and symptoms may include:
- Nausea and vomiting
- Loss of energy and fatigue
- Restlessness and irritability
- Muscle weakness, spasms or cramps
When to see a doctor
If you have a medical condition that increases your risk of hyponatremia, or you have other risk factors for hyponatremia, such as participating in high-intensity activities, and you have the signs and symptoms of low blood sodium, see your doctor.