Dehydration: Hypernatremia and Hyponatremia

Medically Reviewed by Sabrina Felson, MD on May 23, 2023
4 min read

It’s a well-known fact that the human body is more than 60% fluid. In addition to water, your bodily fluids contain vitamins, minerals, and other nutrients that keep the body functioning well. Sodium – an electrolyte – is a critical nutrient for all people. Everyone needs a certain amount of it in their bodies.

If the balance of fluids and sodium is upset, you can experience hypernatremia – having too much sodium and not enough fluid. Or you can experience hyponatremia – having too much fluid and not enough sodium. Both of these conditions can be the result of dehydration.

Dehydration is what happens when your body doesn’t have enough fluids to carry out all its normal functions. Your body needs a balance of water and enough of the nutrients known as electrolytes to work properly. If you dip below the ideal levels for either of those things, you can experience symptoms of dehydration. 

You become dehydrated when you lose fluids and electrolytes, particularly sodium, but you don’t replace them by eating or drinking. Fluids leave your body through sweating, urination, and in the vapor that you breathe out from your lungs. You can lose fluids rapidly due to: 

  • Diarrhea
  • Vomiting
  • Excessive sweating
  • Fever
  • As a side effect of some medications

When you lose a balanced combination of sodium and water, you experience isotonic dehydration. This means both your fluid levels and your sodium levels are lower than they should be. You will need to replace both fluids and sodium if this happens.  

There are also cases where you can lose mainly fluid or mainly sodium. Losing mainly fluid is known as hypertonic dehydration – or hypernatremia. Losing mainly sodium is known as hypotonic dehydration – or hyponatremia.

Hypertonic dehydration (hypernatremia). Hypertonic dehydration happens when you lose water from your body but don’t lose an equal quantity of electrolytes, specifically sodium. You will have too high a sodium concentration in your blood and other bodily fluids. Typically, this causes you to feel thirsty, so that you want to drink water to replace the fluids you lost.

In some cases, you may be losing fluids faster than you can replace them. This may happen due to:‌

  • Vomiting
  • Diarrhea
  • Use of diuretics
  • Excessive sweating
  • Frequent urination due to high blood sugar
  • Kidney disease

If hypernatremia isn’t treated, you could experience worsening thirst. You could go on to develop confusion, muscle twitches, or seizures. In severe cases, hypernatremia can lead to coma and death.

Hypotonic dehydration (hyponatremia). Hyponatremia is what happens when you have too little sodium in your body. This can happen if you lose electrolytes and fluids together but only replace the lost fluids. It may happen if you drink only water and don’t take in other nutrients after losing a lot of fluids from sweating. Doing this will cause an imbalance of fluids and electrolytes.

Hyponatremia can also be the result of some diseases. Some causes of hyponatremia include:‌

  • Kidney failure 
  • Heart failure
  • Liver cirrhosis 
  • Use of diuretics
  • Certain medications, including chemotherapy drugs, anti-seizure medications, or anti-inflammatory drugs
  • Pancreatitis
  • Peritonitis
  • Addison's disease

You might not feel thirsty if you are experiencing hyponatremia, because your fluid levels may be normal. Instead, the first symptoms of hyponatremia may be sluggishness and confusion. Without treatment, you may develop muscle twitches or seizures. Eventually, you could lapse into a coma or die. 

Treatment for all types of dehydration involves replacing fluids and electrolytes in your body. In the case of mild dehydration, you can drink fluids that contain a combination of water and other ingredients to replace salt and other lost nutrients. Sports drinks or rehydration beverages with electrolytes are one option for rehydrating yourself. 

Another option is to drink water and eat a snack to get fluids and sodium into your body. Juice and soda may make diarrhea worse, so use caution in drinking those.

If you or another adult have the following symptoms of severe dehydration, you should seek medical attention:

Severe dehydration symptoms in young children and babies include:‌

  • Sunken soft spot on top of the skull
  • Irritable or listless
  • Dry mouth
  • No tears when crying
  • No wet diapers for 3 hours

A doctor will measure the sodium levels in your blood to determine what type of dehydration you have. Once they know that, they will give you fluids or an electrolyte solution. You may need to have this through an intravenous needle (IV) to speed up your recovery.

Dehydration is a serious health issue. You can prevent dehydration by eating a balanced diet and drinking fluids, especially during exertion or hot weather. If you have underlying conditions that make you susceptible to dehydration, speak to your doctor about what you can do to stay safe.