What Is Hyponatremia?

Hyponatremia (low blood sodium) is a condition that means you don’t have enough sodium in your blood. You need some sodium in your bloodstream to control how much water is in and around the cells in your body.

It can happen because of certain medical conditions, some medicines you might be taking, or if you drink too much water.

Because of the low sodium, the amount of water in your body rises and causes your cells to swell. This can lead to many problems. Some are mild, but others can be serious and even life-threatening.

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How low is too low? Your blood sodium level is normal if it’s 135 to 145 milliequivalents per liter (mEq/L). If it’s below 135 mEq/L, it’s hyponatremia. Your doctor will be able to tell you whether your level is too low.

Hyponatremia Symptoms

You may not have any symptoms if your hyponatremia is very mild. Symptoms usually appear when your level of sodium suddenly rises or drops.

Signs of hyponatremia may include:

  • Nausea with vomiting
  • Fatigue
  • Headache or confusion
  • Cramps or spasms in your muscles
  • Irritability and restlessness
  • Weakness

If you know you are at risk of hyponatremia and start seeing symptoms, call your doctor. If your symptoms are severe, you may need immediate care. Seek emergency care if you have:

Vomiting or nausea

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Loss of consciousness or coma

Hyponatremia Causes

There are a lot of reasons your sodium level might get too low. These include:

Medications. Water pills (diuretics) and some antidepressants and pain medications can make you pee or sweat more. That can affect your sodium level.

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Health problems. Heart failure and kidney or liver disease can affect the amount of fluids in your body, and in turn, your level of sodium.

Bouts of chronic, severe diarrhea or vomiting can deplete your body of fluids and sodium.

Hormone imbalances. Some hormones affect your sodium levels. A condition called SIADH (syndrome of inappropriate antidiuretic hormone) can make you retain water. And a condition called Addison’s disease can affect the hormones that help keep your electrolytes in check. If your thyroid hormone is too low, it can also affect your sodium level.

Drinking too much water. It can dilute the amount of sodium in your blood. It usually happens when people drink too much during endurance events like marathons or triathlons, and also lose sodium through their sweat.

Ecstasy/molly (MDMA). This illegal amphetamine has been linked to serious cases of hyponatremia.

Hyponatremia Risk Factors

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Since older adults are usually more likely to take certain medications or develop chronic diseases, they’re generally more likely to get hyponatremia. But at any age, you’re more likely to get it if you have certain conditions, including:

Kidney disease

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

Heart failure

Diabetes insipidus

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Cushing’s syndrome

Primary polydipsia, a psychiatric condition that makes you want to drink lots of water

It can also happen if you take the drugs that make the condition more likely.

If you drink too much water when you do something that’s physically very hard -- like a marathon -- you may be more likely to develop hyponatremia.

Hyponatremia Diagnosis

Because the symptoms of hyponatremia can vary so much from person to person, your doctor will probably order blood and urine tests to confirm the diagnosis. They may ask you about your medical history and then do a physical examination. But they’ll need to see your test results to make sure you have hyponatremia.

Hyponatremia Treatments

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Since so many different things can cause hyponatremia, your treatment depends on the cause.

If your doctor thinks you drink too much water, you may need to cut back. If you take diuretics, your doctor may make a change in your treatment so the sodium in your blood can go back to a normal level.

If your hyponatremia came on suddenly and it’s severe, you’ll need emergency treatment to boost your sodium level and monitoring to make sure that it happens safely. You may need to stay in the hospital and have:

IV infusion with a sodium solution to slowly raise levels in your blood over a few days

Prescription medications to control problems like headaches, nausea, or seizures

Hyponatremia Complications

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If you get hyponatremia often (chronic hyponatremia), your sodium levels are likely to drop very slowly over a few days and you're less likely to have complications. But with acute hyponatremia, your sodium levels drop very quickly. This can cause:

Rapid brain swelling



You’re at higher risk of getting brain damage from hyponatremia if you’re a woman who hasn’t gone through menopause. Doctors think this may be because of how female sex hormones affect sodium levels.

Hyponatremia Prevention

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There are several ways you may be able to prevent hyponatremia:

If you have a condition that can lead to low blood sodium, like adrenal gland insufficiency, make sure you get it treated.

Know the symptoms of hyponatremia. Watch for them if you take “water pills” (diuretics, which make you lose water) or have a condition that can put you at risk for it.

Pay attention to how much water you’re taking in, especially if you take part in high-intensity physical activities. There are two reliable ways to know how much water you should have: your thirst and the color of your urine. You’re probably getting enough water if you don’t feel thirsty and your urine is a pale yellow color.

Ask your doctor if you should drink sports beverages instead of water while doing intense physical activities. These drinks have electrolytes that include sodium. But if you’re not working out really hard or for a long period of time, you might not need them.

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