High blood pressure but low sodium levels

Sodium is an electrolyte that balances the amount of fluid in the body, helps muscles and nerves work, and regulates blood pressure. 

Sodium is a mineral naturally found in many foods. It is one of several minerals essential for the body to function, and it is the main determinant of the balance of water in the body. But it has many jobs beyond this, including a regulator of blood pressure and muscle contraction. 

Although we get our sodium from food, the body has many ways to maintain the right amount of sodium in the body. When sodium levels become abnormal, there can be important health implications. 

Here, we will review reasons someone’s sodium level can get too high, and what it means when this happens.

What causes low sodium (hyponatremia)?

Hyponatremia, or a low sodium level, is the most common electrolyte problem. Sodium levels in the blood are affected by how much sodium we eat or how much water we drink. However, the body adjusts for variations in our diet in order to maintain normal sodium levels. Below are some of the common causes of hyponatremia.

Kidney problems

The kidneys play a critical role in controlling the amount of sodium and water in the blood. So, the most common reason for low sodium is a kidney problem. When the kidneys are not functioning normally, which can be seen in chronic kidney disease or even temporary dehydration, the body holds too much water. And the proportion of sodium compared to water in the body lowers the sodium level. 

Medications

Low sodium can also be a side effect of some drugs and medications. These include:

• Diuretics, which are commonly prescribed for high blood pressure or heart failure.

• Angiotensin-converting enzyme inhibitors (ACE inhibitors), another common blood pressure medication.

• Antidepressants, especially selective serotonin reuptake inhibitors (SSRIs).

• Some antipsychotics and antiepileptics.

• Amiodarone, a heart medicine that helps to regulate the heart rhythm.

• Theophylline, a medicine for people with certain lung conditions.

• Intravenous fluids.

• Certain drugs, like ecstasy (methylenedioxymethamphetamine).

Medical conditions

Certain medical conditions can put people at higher risk of hyponatremia.  Some examples of these include: 

• Conditions that can cause the body to hold onto too much fluid, like heart failure or liver cirrhosis.

• Diarrhea, which can cause your body to lose a lot of electrolytes.

• Syndrome of inappropriate antidiuretic hormone secretion (SIADH), which causes the body to retain water.

• Having low levels of certain hormones like thyroid hormone, cortisol, or aldosterone.

• Drinking too much water — although this is uncommon and mostly seen in people with psychiatric problems or in athletes who over-hydrate after intense exercise.

Lab measurement error

Abnormal sodium levels may also result from measurement errors. Your provider needs to look at the big picture if your sodium level is low. High blood sugar can make sodium levels appear low, even if the total amount of sodium in the body is normal. Having very high lipid levels in the blood can also lead to incorrect sodium measurements. 

What are the symptoms of low sodium levels? 

The symptoms of hyponatremia are related to the way it causes fluid shifts in the brain. The severity of symptoms depends on both the sodium levels and how fast sodium levels change. 

Your body can usually adapt to small changes in sodium levels over time. Rapid changes in sodium (that happen over 1-2 days) tend to be more dangerous, since your body does not have time to adjust to fluid shifts.

Abrupt changes in sodium levels can lead to symptoms that range from mild to severe.

• More severe symptoms include:

  • Lethargy, or being much more tired and inactive than usual

  • Confusion, disorientation, or hallucinations

• Very severe symptoms include:

  • Seizures 

  • Coma, or becoming unconscious 

  • Respiratory arrest, or stopping breathing

The symptoms of chronic hyponatremia, which happens over several days to weeks, are usually less severe. And they may also be less easy to recognize since they are not very specific. Some symptoms of chronic hyponatremia are:

• Fatigue

• Nausea

• Dizziness

• Vomiting

• Difficulty walking/falls

• Confusion or being forgetful

• Muscle cramps

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GoodRx Health information and resources is reviewed by our editorial staff with medical and healthcare policy and pricing experience. See our editorial policy for more detail. We also provide access to services offered by GoodRx and our partners when we think these services might be useful to our visitors. We may receive compensation when a user decides to leverage these services, but making them available does not influence the medical content our editorial staff provides.

How low is too low?

Hyponatremia is always diagnosed with a blood test, usually a blood electrolyte panel. Your doctor might check your sodium levels routinely if you are on a medication that can cause low sodium. Or it may be discovered on a blood test that is ordered for a different reason.

The definition of low sodium is a blood level that is lower than 135 mEq/L. In the case of chronic or long-standing hyponatremia, most people don't have symptoms unless the level is less than 120 mEq/L. Your provider can also run other blood tests or urine tests better to understand the cause of your low sodium levels. 

How do you treat low sodium levels?

The most important treatment for low sodium is treating the underlying cause. Your provider will make sure you are getting the best treatment for your illness while correcting your sodium levels.

In cases of mild hyponatremia, you may not need immediate treatment. Your provider may want to check the amount of sodium in the blood periodically. If the low sodium is caused by medication, your provider may want to stop or change your medicine. If you must be on a medication that causes your sodium to be low, your provider might recommend dietary changes. Or they may recommend you take sodium supplements or limit the amount of water you drink. However, it’s best to only make these changes under your provider's guidance.

People with extremely low sodium levels or with severe symptoms should be treated in the hospital, where they can receive medications and intravenous fluids to help bring sodium levels back to normal in a gradual and safe way. 

The bottom line

Sodium is a vital mineral that plays an important role in many bodily functions. So, when levels get too low, it can cause some problems — particularly with fluid levels, blood pressure, and brain function. 

Some common medical problems and medications can lower sodium levels. And, for most people, their symptoms will be mild, and the problem can easily be fixed. But more serious cases will lead to noticeable symptoms, and these cases are best treated in the hospital. 

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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