Hyponatremia: Low Sodium Levels in the Blood

Medically Reviewed by Jabeen Begum, MD on December 01, 2023
7 min read

Hyponatremia is a condition that happens when you don’t have enough sodium in your blood. We often try to limit how much salt (sodium) is in the foods we eat, but it’s important to remember that our body needs a little bit. 

You need some sodium in your bloodstream to control how much water is in and around the cells in your body. When you have low sodium in your blood, the amount of water in your body rises and causes your cells to swell. This can lead to some mild and other serious and even life-threatening problems.

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

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

What specialist treats hyponatremia?  Hyponatremia has many causes and can affect many different parts of your body, so it can be treated by many different doctors. For example, you might see your primary care doctor or a doctor who specializes in kidney health (nephrologist), elder care (geriatrician), hormonal health (endocrinologist), or other doctors who specialize in other areas of medicine. These doctors might suggest different plans for treating hyponatremia.

There are a few types of hyponatremia:

  • Euvolemic hyponatremia happens when your total body water increases but your sodium level stays the same.
  • Hypovolemic hyponatremia is when your body loses more water than sodium. 
  • Hypervolemic hyponatremia happens when your body gains both, but gains more water than sodium.

Other types of hyponatremia include:

  • Dilutional hyponatremia is when you drink too much water that is not fortified with electrolytes and salts. 
  • Hyposmolar (or hypotonic) hyponatremia happens when you don’t have enough electrolytes. It can be caused by other forms of hyponatremia.

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

Moderate to severe signs of hyponatremia may include:

  • Nausea with vomiting
  • Fatigue or low energy
  • Headache
  • Confusion
  • Cramps or spasms in your muscles
  • Crankiness 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 should seek care right away. 


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.
  • 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.
  • 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.
  • Drinking too much alcohol. Alcohol is a natural diuretic, which means it makes you pee more and lose sodium when you vomit.
  • Ecstasy/molly (MDMA). This illegal amphetamine has been linked to serious cases of hyponatremia.
  • Severe burns on a large part of the body. Loss of water from a burn wound can affect the balance of water in your body.

Hyponatremia can happen if you take certain drugs. You’re also more likely to get it if you have certain conditions, including:

  • Kidney disease
  • Recent surgery
  • Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
  • Heart failure
  • Diabetes insipidus
  • Cushing’s syndrome
  • Primary polydipsia, a psychiatric condition that makes you want to drink lots of water 
  • Cirrhosis

Other things that may put you more at risk of hyponatremia include:

Age. Older adults are generally more likely to get hyponatremia because they're more prone to develop chronic conditions that can result in a sodium imbalance. Changes related to aging and taking certain medications also play a role in the risk of hyponatremia in older adults.

Climate. The climate can also affect your risk of hyponatremia. For example, warm weather can cause you to sweat, which affects your sodium levels. Some research shows that hyponatremia happens more often when the temperature is above 15ºC (59ºF), although the threshold temperature might vary by region.

Physical activity. If you drink too much water when you do something that’s physically very hard – like running a marathon – you may be more likely to get hyponatremia.

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. Some common tests include: 

  • Basic metabolic panel,which includes a sodium blood test that looks at the concentration level of sodium in the blood
  • Blood osmolality test, which looks at dissolved particles in your blood and can confirm imbalances
  • Urine osmolality, a test that helps measure the concentration of chemicals in pee, with lower osmolality results confirming low blood sodium levels
  • Urine sodium tests, which can find out the cause of abnormal sodium blood levels and can confirm whether your kidneys are causing sodium removal from your body

Usually, healthy sodium levels in the blood are 135-145 mEq/L (or mmol/L).

Your doctor may ask you about your medical history and then do a physical examination. But they’ll need to see your test results to confirm whether you have hyponatremia.

Since so many things can cause hyponatremia, your treatment depends on the cause of the condition and how severe it is.

If you take diuretics or other drugs that can cause fluid imbalances or hyponatremia, your doctor may make a change in your treatment so the sodium in your blood can go back to a normal level. If the low blood sodium was caused by a medical condition, then your best bet is to talk to your doctor about how to manage that condition.

If your hyponatremia came on suddenly and it’s severe, you’ll need emergency treatment to boost your sodium level. Don’t try to treat yourself at home: Rebalancing sodium and water levels is a delicate process, and medical staff need to monitor the process to make sure it happens safely. You may need to stay in the hospital and have:

  • An IV with a sodium solution to slowly raise levels in your blood over a few days
  • Prescription medications to control symptoms like headaches, nausea, or seizures

If you have chronic hyponatremia, your sodium levels are likely to drop very slowly over a few days and your symptoms and complications will be milder. With acute hyponatremia, your sodium levels drop very quickly. This can cause:

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

Some research suggests that hyponatremia, both chronic and acute, can also increase your risk for bone fractures and osteoporosis.

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.

You should increase your water intake under certain conditions:

  • Hot weather and high altitudes. Being in the heat or in humid weather can cause you to sweat and increase the need for more fluid, and being at a high altitude can cause you to be dehydrated.
  • Health concerns. When you have diarrhea, a fever,  or are vomiting, your body loses fluid. Bladder infections and urinary tract stones also require an increase in fluids.
  • During pregnancy and while breastfeeding. You'll need more water if you're pregnant or breastfeeding, as these conditions can also cause you to be dehydrated.
  • Before, during, and after a workout. You lose fluid when you sweat, so it's important to stay hydrated while exercising. 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.